a597e932a2c00ea8123a9dd0641d79a80c9d1e31dfb0d9cada251f62b40bd445

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+– in Africa  (light blue & dark grey)– in the African Union  (light blue)  —  [Legend]
+
+Burkina Faso is a country in West Africa. It used to be called Upper Volta and the name was changed to Burkina Faso in 1984. The country was once ruled by France, but it has been independent since 1960. The capital is Ouagadougou.
+
+In 2005, about 13,228,000 people lived in the country. It is next to Mali, Niger, Benin, Togo, Ghana and Côte d'Ivoire. It does not have any coast with an ocean or sea. People from Burkina Faso are called Burkinabé (pronounced burr-KEE-na-bay).
+
+People have lived in the area of Burkina Faso for thousands of years. At first, they were hunter-gatherers, hunting animals and collecting fruits and vegetables.[6] Later they became farmers. People called the Mossi arrived between the 11th and 13th centuries.[6] They ruled the area until the end of the 19th century. In 1896 France beat the Mossi kingdom and became the colonial rulers of Burkina Faso. After World War I, the country was called Upper Volta.
+
+In 1960, Upper Volta became independent from France. The first president of the new country was Maurice Yaméogo. After he became the president, Yaméogo banned other political parties. For several years the people of Upper Volta were very unhappy with the government and in 1966 the military took over in a military coup. In 1983 the government was taken over again by military men called Thomas Sankara and Blaise Compaoré. Sankara became president. In 1984, he changed the name of the country to Burkina Faso. It means "land of honest people".[7]
+
+In December 1985, Burkina Faso went to war for five days with near-by country Mali. In 1987, there was another military coup and Sankara was assassinated (murdered). Blaise Compaoré became the president.
+
+On 28 October 2014 protesters began to march and demonstrate in Ouagadougou. Compaoré was ready to change the constitution and extendhis 27-year rule. On 30 October 2014, some protesters set fire to the parliament.[8] They also took over the national television headquarters.[9] On 31 October 2014, President Compaoré, resigned after 27 years in office.[10]
+
+In 2015 the country held their first election. Roch Marc Christian Kabore, a former Prime Minister, was elected as President.[1]
+
+Burkina Faso is divided into thirteen regions, forty-five provinces, and 301 departments. The regions are:
+
+Below is a list of the largest cities in Burkina Faso.  For other cities see List of cities in Burkina Faso.
+
+Burkina Faso is made up of two major types of countryside. The larger part of the country is covered by a peneplain.  It has a gently undulating landscape with a few isolated hills. The southwest of the country forms a sandstone massif. The highest peak, Ténakourou, is found at an elevation of 749 meters (2,457 ft). The area is bordered by sheer cliffs up to 150 meters (492 ft) high. The average altitude of Burkina Faso is 400 meters (1,312 ft).  The difference between the highest and lowest terrain is no greater than 600 meters (1,969 ft). Burkina Faso is a mostly flat country.
+
+Burkina Faso has a tropical climate with two distinct seasons. In the rainy season, the country receives between 600 and 900 millimeters (23.6 and 35.4 in) of rainfall. In the dry season, the harmattan – a hot dry wind from the Sahara – blows. The rainy season lasts about four months, from May/June to September. It is shorter in the north of the country.
+
+Burkina Faso's natural resources include manganese, limestone, marble, phosphates, pumice, salt and small deposits of gold.
+
+Burkina Faso's fauna and flora are protected in two national parks and several reserves.
+
+Literature in Burkina Faso is based on the oral tradition, which remains important.  Since the 1970s, literature has developed in Burkina Faso with many more writers being published.[12]
+
+There is also a large artist community, especially in Ouagadougou.  Much of the crafts produced are for the growing tourist industry.
+
+The food of Burkina Faso, typical of west African cuisine, is based around staple foods of sorghum, millet, rice, maize, peanuts, potatoes, beans, yams and okra.[13] The most common sources of protein are chicken, eggs and fresh water fish.

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+The Nagorno-Karabakh Republic (NKR) [3] (Armenian: Լեռնային Ղարաբաղ Հանրապետություն Lernayin Gharabaghi Hanrapetut’yun) or Artsakh Republic[3] is a de facto independent republic in the Nagorno-Karabakh region of the South Caucasus. It is internationally recognised to be part of Azerbaijan.
+
+The Nagorno-Karabakh region has been populated by Armenians for a long time. The area has been disputed by Armenia and Azerbaijan since 1918. After the Soviet Union established control over the area, in 1923 it formed the Nagorno-Karabakh Autonomous Oblast (NKAO) within the Azerbaijan SSR. In the final years of the Soviet Union, the region again became a source of dispute between Armenia and Azerbaijan, resulting in the Nagorno-Karabakh War from 1988–1994.
+
+On 10 December 1991, a referendum was held in the NKAO and the neighboring Shahumian region. This resulted in a declaration of independence from Azerbaijan as the Nagorno-Karabakh Republic. The country is not recognized by any UN member state, including Armenia. Representatives of the governments of Armenia and Azerbaijan have since been holding peace talks mediated by the OSCE Minsk Group.
+
+The Artsakh Republic has a lot of mountains. It is 11,500 km2 (4,440 sq mi) in area, and borders Armenia, Azerbaijan, and Iran. The highest peaks in the country are Mount Mrav, 3,340 metres (10,958 ft), and Mount Kirs 2,725 metres (8,940 ft). The major rivers are the Terter and Khachen rivers.[4] Most rivers in the country flow towards the Artsakh valley.[5]
+
+The climate in the Artsakh Republic is mild. It is foggy for over 100 days a year. More than 36% of the country is forested.
+
+In 2005, the country's population was 137,737. The ethnic composition was 137,380 (99.74%) Armenians, 171 (0.12%) Russians, 21 (0.02%) Ukrainians, 6 (0.00%) Azerbaijanis and 159 (0.12%) others.
+
+The first demographic census in the Artsakh Republic took place in 1769. It was a letter from Heraclius II of Georgia to Russia's Petr Ivanovich Panin, and said, "Seven families rule the region of Khamse. Its population is totally Armenian." [6][7]
+
+In 2014, the life expectancy for males was 71.6 years, and females 76.8 years.[8]
+
+Nearly all of the Azerbaijani population was killed or thrown out by Armenian forces since the war. Azerbaijani refugees who have survived not allowed to return and have become displaced.[9]

ensimple/2427.html.txt

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+Hawaii is a U.S. state and the only U.S. State that is in Oceania. It is the last state that joined the United States, becoming a state on August 21, 1959. It is the only state made only of islands. Hawaii is also the name of the largest island. The capital and largest city of Hawaii is Honolulu on the island named Oahu.
+
+Hawaii is known as the "Aloha State". Aloha is a Hawaiian word that has many meanings like welcome, hello and goodbye. Aloha also means love and care. The different meanings are brought together in the term "Aloha Spirit" to describe the friendly people of Hawaii.
+
+Hawaii is an archipelago, a long chain of islands. There are eight main islands and many small islands and atolls. They are the tops of underwater volcanos. The main islands are Niihau, Kauai, Oahu, Molokai, Lanai, Kahoolawe, Maui and Hawaii.
+
+The first people of Hawaii were Polynesians. They came to the islands sometime between 200 and 600 AD. Captain James Cook is given credit for discovering the islands for the Europeans in 1778. Others may have been there before him. Captain Cook named the islands the Sandwich Islands for the fourth Earl of Sandwich, John Montague.
+
+Kamehameha I was the first king of Hawaii. He united the separate small Hawaiian kingdoms into one large kingdom in 1795. In 1893, American soldiers stopped Queen Liliuokalani from leading Hawaii when American business people took over the government and made their own laws. She was the last monarch of Hawaii. She also wrote the original words of the song called Aloha Oe.
+
+The American business people made Hawaii into a republic for a short time. The new leader, Sanford Dole was called the President of Hawaii. In 1898, the United States of America took over the government and made Hawaii into a territory. In 1959, Hawaii became the fiftieth American state.
+
+The biggest industry of Hawaii is tourism. Almost 7 million people visited in 2000. Important exports are sugar, pineapple, macadamia nuts, and coffee.
+
+Popular tourist sites include Waikiki Beach, Hawaii Volcanoes National Park, Polynesian Cultural Center, and the USS Arizona Memorial at Pearl Harbor.
+
+The state flower is the yellow hibiscus (Hibiscus brackenridgei or ma'o hau hele). The state bird is the Hawaiian goose (nene). The state fish is the reef triggerfish, also called the humu humu nuku nuku apua'a. The state tree is the candlenut, also called kukui. The state song is Hawaii Ponoi. The state motto is Ua mau ke ea o ka aina i ka pono. In English it says, The life of the land is perpetuated in righteousness.
+
+Notes
+
+Media related to Hawaii at Wikimedia Commons

ensimple/2428.html.txt

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+Hawaii is a U.S. state and the only U.S. State that is in Oceania. It is the last state that joined the United States, becoming a state on August 21, 1959. It is the only state made only of islands. Hawaii is also the name of the largest island. The capital and largest city of Hawaii is Honolulu on the island named Oahu.
+
+Hawaii is known as the "Aloha State". Aloha is a Hawaiian word that has many meanings like welcome, hello and goodbye. Aloha also means love and care. The different meanings are brought together in the term "Aloha Spirit" to describe the friendly people of Hawaii.
+
+Hawaii is an archipelago, a long chain of islands. There are eight main islands and many small islands and atolls. They are the tops of underwater volcanos. The main islands are Niihau, Kauai, Oahu, Molokai, Lanai, Kahoolawe, Maui and Hawaii.
+
+The first people of Hawaii were Polynesians. They came to the islands sometime between 200 and 600 AD. Captain James Cook is given credit for discovering the islands for the Europeans in 1778. Others may have been there before him. Captain Cook named the islands the Sandwich Islands for the fourth Earl of Sandwich, John Montague.
+
+Kamehameha I was the first king of Hawaii. He united the separate small Hawaiian kingdoms into one large kingdom in 1795. In 1893, American soldiers stopped Queen Liliuokalani from leading Hawaii when American business people took over the government and made their own laws. She was the last monarch of Hawaii. She also wrote the original words of the song called Aloha Oe.
+
+The American business people made Hawaii into a republic for a short time. The new leader, Sanford Dole was called the President of Hawaii. In 1898, the United States of America took over the government and made Hawaii into a territory. In 1959, Hawaii became the fiftieth American state.
+
+The biggest industry of Hawaii is tourism. Almost 7 million people visited in 2000. Important exports are sugar, pineapple, macadamia nuts, and coffee.
+
+Popular tourist sites include Waikiki Beach, Hawaii Volcanoes National Park, Polynesian Cultural Center, and the USS Arizona Memorial at Pearl Harbor.
+
+The state flower is the yellow hibiscus (Hibiscus brackenridgei or ma'o hau hele). The state bird is the Hawaiian goose (nene). The state fish is the reef triggerfish, also called the humu humu nuku nuku apua'a. The state tree is the candlenut, also called kukui. The state song is Hawaii Ponoi. The state motto is Ua mau ke ea o ka aina i ka pono. In English it says, The life of the land is perpetuated in righteousness.
+
+Notes
+
+Media related to Hawaii at Wikimedia Commons

ensimple/2429.html.txt

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+Hayao Miyazaki (宮崎 駿, Miyazaki Hayao, born January 5, 1941) is a leader in the area of anime, or Japanese animation. His name is pronounced "Ha-ya-oh Me-ya-za-key". He worked with Isao Takahata.
+
+His company made the animated movies Spirited Away (2001), My Neighbor Totoro (1988), Kiki's Delivery Service (1989), Porco Rosso (1992) and Princess Mononoke (1997).
+
+His company is named Studio Ghibli. In 2001, he won the Academy Award for Best Animated Feature for Spirited Away. It was the first anime to win the award in that category.
+
+During a press conference at Italy's Venice Film Festival, he announced that he was going to retire from the production of feature-length films.[1]
+
+Miyazaki announced his retirement on September 2, 2013.[2]

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+When two straight lines come together they make an angle. The two lines are called the sides[1] of the angle and they meet at a point. A flat surface (called a plane) also forms an angle when it meets another.
+
+To measure the size of an angle, we use units called degrees. A degree is a standard unit and we use the symbol ° after a number to show that it is a number of degrees. We can use a decimal number or a fraction for part of a degree, but a degree can also be divided into 60 minutes (1° = 60') and a minute can be divided into 60 seconds (1' = 60"). So 22.5°, 221⁄2° and 22° 30' are all the same angle. In mathematics, angles are often measured in radians instead of degrees 
+
+
+
+(
+2
+π
+
+
+ rad
+
+
+=
+
+360
+
+∘
+
+
+
+
+{\displaystyle (2\pi {\mbox{ rad}}=360^{\circ }}
+
+, so 
+
+
+
+
+22.5
+
+∘
+
+
+=
+
+
+
+π
+8
+
+
+
+
+
+ rad
+
+
+)
+
+
+{\displaystyle 22.5^{\circ }={\tfrac {\pi }{8}}{\mbox{ rad}})}
+
+.
+
+Angles are studied in geometry, where an angle where edges meet is often called a vertex. For example, the three sides of a triangle are its edges and two of the edges meet at each vertex. Similarly, two of the six sides (or faces) of a cube meet at each of its twelve edges and three edges meet at each of its eight corners (or vertices, which is the plural of vertex).
+
+An acute angle is an angle less than 90° (but more than 0°). A right angle is an angle equal to 90°. An obtuse angle is an angle greater than 90° but less than 180°. A straight angle (or straight line) is an angle equal to 180°. A reflex angle is an angle greater than 180° but less than 360°.
+
+Supplementary angles are two angles with the sum equal to 180°.
+
+Two angles that sum to one right angle (90°) are called complementary angles.
+
+Two angles that sum to one full circle (360°) are sometimes called explementary angles or conjugate angles.
+
+People usually use a protractor to measure and draw angles. Sometimes, people use a 360° protractor to measure angles.

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+Hayden Christensen (born April 19, 1981) is a Canadian actor. He was in Canadian television programs when he was young, then he went to act into American television in the late 1990s. He did minor acting roles before being praised for his role of Sam in Life as a House. He became very famous worldwide by playing the young adult Anakin Skywalker in the Star Wars movies.
+
+Christensen was born in Vancouver, British Columbia and raised in Thornhill, Ontario. In 2007, he began dating actress Rachel Bilson. They met while making Jumper. They became engaged on December 25, 2008.[1][2] In mid-2010, the couple split up, but were dating again a few months later.[3][4][5][6]
+
+Christensen performed a public service announcement for Do Something's Teens for Jeans Campaign in 2008.[7] He was a model in Louis Vuitton's advertising.[8] He is in RED’s new Lazarus Effect Campaign, which is to increase awareness for its efforts to fight AIDS in Africa.[9][10]
+
+
+
+
+
+
+

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+Joseph Haydn (also known as Franz Joseph Haydn) was an Austrian composer. He was born on March 31 or April 1, 1732, and died on May 31, 1809. He was one of the most famous composers in the Classical music period. He is often called the "Father of the Symphony."
+
+Haydn's father made wheels for a living, and had the skills of a blacksmith, stonemason, and carpenter. He used that skill in his spare time to make musical instruments for his family to play. The Haydn family would give informal weekend concerts. One of Joseph's relatives thought that Joseph had a great singing voice and should go with him to a boarding school where he would start studying to become a priest.
+
+Haydn did not like it very much at the boarding school, but his voice developed to a point where he was selected to be a part of the Boy's Choir of the Vienna Cathedral. He stayed there until his voice changed.
+
+Haydn made a living teaching lessons and playing in the streets for handouts until he met Nicolai Porpora, who hired Haydn as an accompanist and general servant.
+
+Eventually Haydn got a job working for Nicholas Esterhazy. He worked for the Esterhazys for over 30 years. He wrote symphonies, string quartets, operas, piano sonatas, and other pieces.
+
+After he was released from his duties with the Esterhazys, Haydn travelled to London. Even at the age of 60 he was still active and wrote some of his most famous symphonies there.
+
+While in London, he heard Handel's Messiah, and was inspired to write two oratorios of his own, The Seasons and The Creation.
+
+While working on these oratorios in Vienna, Haydn gave lessons to Ludwig van Beethoven. Beethoven had first wanted to study with Mozart, but by the time Beethoven was ready to study in Vienna, Mozart had died.
+
+The house in Vienna where Haydn wrote his oratorios has been turned into a museum called 'haydnhaus'.
+
+Haydn was so well-respected in Vienna that he was known as "Papa Haydn" and his influence on music was profound and great.

ensimple/2432.html.txt

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+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2433.html.txt

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+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

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+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/2435.html.txt

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+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2436.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2437.html.txt

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+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/2438.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2439.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/244.html.txt

@@ -0,0 +1,50 @@
+
+
+– in the European continent  (light green & grey)– in the United Kingdom  (light green)
+
+England is a country in Europe. It is a country with over sixty counties in it. It is in a union with Scotland, Wales and Northern Ireland. All four countries are in the British Isles and are part of the UK.
+
+Over 55 million people live in England (2015 estimate). This is 84% of the population of the UK.[2] The capital city of England is London, which is also the biggest city in the country. Other large cities in England are Birmingham, Liverpool, Manchester and Leeds.
+
+The English flag is a red cross on a white background. This cross is the cross of Saint George, who is the patron saint of England. Some other symbols used for England are a red rose and three lions.
+
+England is the largest part of the island of Great Britain, and it is also the largest constituent country of the United Kingdom. Scotland and Wales are also part of Great Britain (and the UK), Scotland to the north and Wales to the west. To the east and south, and part of the west, England is bordered by sea. France is to the south, separated by the English Channel. The Channel Tunnel, (Chunnel) under the English Channel, connects England to northern France (and the rest of mainland Europe). Ireland is a large island to the west, divided into Northern Ireland which is part of the United Kingdom, and the Republic of Ireland.
+
+London is the largest city and the capital. Other large cities are Birmingham, Manchester, Leeds, Sheffield, Bristol, Nottingham and Liverpool. The longest river in England is the River Severn. Other large rivers are the Thames (which runs through London), the Trent and the Humber.
+
+England was named after a Germanic tribe called the "Angles", who settled in Central, Northern, and Eastern England in the 5th and 6th centuries. A related tribe called the "Saxons" settled in the south of England. That is why that period of English history is called "Anglo-Saxon". For the majority of this time, England did not exist as a united country. The Anglo-Saxons lived in many small kingdoms, which slowly united. The later countries of England and Wales were formed from the earlier Roman Britain.
+
+The English kingdoms fought both the Scots,who were also uniting into one kingdom, and Danish invaders, who formed their own country in the East and North. Many villages and towns in this area (particularly in Yorkshire and Lincolnshire) have Danish names, and use some Danish-based words. At one time Wessex (in the West of England) was the only English kingdom left. After many battles, King Alfred the Great of Wessex became king of the whole of England, and the old kingdoms (Mercia, Northumbria, etc.) just became provinces, called "Earldoms" governed by an "Earl". By 927 Alfred's grandson Athelstan was the king of all of England not controlled by the Danes.
+War with the Danes continued and from 1016 to 1042, the king of Denmark (Knut or Canute,who died in 1035,and then his sons) ruled England.
+
+When King Edward the Confessor died, Harold Godwinson (the Earl of Wessex) became king. William the Conqueror, Duke of Normandy (today part of northern France), said that Harold had promised to make William the king. He invaded England and fought King Harold at the Battle of Hastings in 1066. William won, and became king of England.[3]
+
+The kings of England spoke French for the next 300 years.[4] England took over the country of Wales in the 13th century. There were many wars, often against France and Scotland.
+
+For several centuries the religion of England was Roman Catholicism. The bishops (church leaders) of England and all their churches obeyed the Pope and the church in Rome, Italy. During the Protestant Reformation many did not agree with this. In the 1530s, the Pope told King Henry VIII that he could not divorce his wife. King Henry VIII created the Church of England (a "Protestant" church) partly so that he could divorce his wife. He made Protestantism the official church in England. For the next 200 years, there was struggle over whether the King (or Queen) of England should be "Roman Catholic" or "Protestant".
+
+Queen Elizabeth I was Henry's second daughter. She was a powerful queen who ruled for more than 40 years. When Queen Elizabeth I died, she had no children, and in 1603 James VI of Scotland (the son of Mary, Queen of Scots) became King James I of England. He called his two countries "Great Britain", but they were still separate countries with their own parliaments and laws, even though they were in personal union. They shared the same monarch.
+
+James' son, Charles I and the English Parliament fought each other in the English Civil War (Scotland and Ireland were involved as well, but the story is complicated!). Oliver Cromwell became leader of the Parliamentary Army (the "Roundheads") and defeated the Royalist Army (the "Cavaliers"). King Charles was beheaded in 1649 and Oliver Cromwell became dictator ("Lord Protector"). When Cromwell died, his son Richard was not strong enough to rule, and Charles II, the son of Charles I, was invited to come to England and be king in 1660.
+
+When King Charles II died, his brother James II was the next king. A lot of people did not like James because he was Roman Catholic. William of Orange was invited to invade England.[5] He was the ruler of part of the Netherlands and husband of Mary, the daughter of King James. Many people welcomed William because he was a Protestant. James left the country without a fight and Parliament asked William and Mary to become King and Queen together. When Mary II of England died, William ruled alone. Queen Mary's sister Anne became the next queen. While she was queen, England and Scotland were officially joined as one country. This was called the Acts of Union 1707. It also merged their separate parliaments. The parliament in London now included Scottish Members of Parliament ("MPs"), and was called the Parliament of Great Britain.
+
+After this, the history of England becomes the history of Great Britain and United Kingdom.
+
+The United Kingdom was formed in 1800, when the Irish Parliament merged with the British one. later on, many in Ireland fought against this merger. The result was the separation of the Republic of Ireland. This is not the whole island of Ireland. The rest of the island, Northern Ireland, is now the only part of Ireland still in the UK. England is the only country of UK not to have its own government, Parliament or Assembly, but is governed by Parliament of the United Kingdom. Seats in Parliament are decide by the number of electors in the various parts of the UK.
+
+The English language is a West Germanic language spoken in many countries around the world. With around 380 million native speakers, it is the second most spoken language in the world, as a native language. As many as a billion people speak it as a second language. English is an influence on, and has been influenced by many different languages. Some people in England speak other languages, such as Welsh.
+
+All of Great Britain has an oceanic climate. There can be a temperature difference of 5-10°c between the north and the south (the north is generally colder), and there is often snow in the north before there is in the south.
+
+The prevailing wind for most of the year is from the Atlantic, to the west of England. Therefore, there is more rain on the western side of the country. The east is colder and drier than the west. The country usually has a mild climate because the Gulf Stream to the western side is warm water. The climate is warmer than it was 200 years ago, and now ice and snow are rare in the southern part of the country. Occasionally, air from the Arctic Circle comes down the eastern side of the country and the temperature can drop below 0oC.
+
+See English literature,
+English Heritage,
+Aldeburgh Festival
+
+The English football team won the World Cup in 1966. They came close in Italy 1990, closely losing in the semi-final against West Germany on penalties. In the 2006 World Cup they got to the quarter finals, then lost to Portugal after penalty kicks. In the 2018 FIFA World Cup, they came close again only to be knocked out in the semi-final, losing 2-1 to Croatia.
+
+English people invented:
+
+There are many well known English people. Here are just a few of them:

ensimple/2440.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2441.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2442.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2443.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2444.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2445.html.txt

@@ -0,0 +1,55 @@
+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/2446.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2447.html.txt

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+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

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+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2449.html.txt

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+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

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+English is a West Germanic language. It was first spoken in Anglo-Saxon England in the early Middle Ages. It is spoken in many countries around the world. Anglophone countries include the United Kingdom, the United States, Canada, Australia, Ireland, New Zealand and a number of Caribbean nations. There are about 375 million native speakers (people who use English as their first language),[4] which is the largest after Mandarin and Spanish. About 220 million more people use it as their second language. It is often used in work and travel, and there are at least a billion people who are learning it. This makes English the second most spoken language, and the most international language in the world.
+
+English has changed and developed over time.[5] The most obvious changes are the many words taken from Latin and French. English grammar has also become very different from other Germanic languages, without becoming much like Romance languages. Because nearly 60% of the vocabulary comes from Latin, English is sometimes called the most Latin of the Germanic languages, and is often mistaken for being a Romance language.[6]
+
+As its name suggests, the English language began in England. Germanic tribes (Saxons, Angles, and Jutes) came to Britain from around 449 AD. They made their home in the south and east of the island, pushing out the Celtic Britons who were there before them, or making them speak the English language instead of the old Celtic languages. Some people still speak Celtic languages today, in Wales (Welsh) and elsewhere. Gaelic is the Scottish Celtic language, still spoken by some in the Scottish Highlands and Islands. "Scots" is a dialect of English (although some call it a separate language). Irish Gaelic is spoken by very few people today.
+
+The Germanic dialects of these different tribes became what is now called Old English. The word "English" comes from the name of the Angles: Englas. Old English did not sound or look much like the English spoken today. If English speakers today were to hear or read a passage in Old English, they would understand just a few words.
+
+The closest language to English that is still used today is Frisian, spoken by about 500,000 people living in the Netherlands, Germany and Denmark. It is much like English, and many words are the same. The two languages were even closer before Old English changed to Middle English). Today, speakers of the two languages would not be able to understand each other. Dutch is spoken by over 20 million people, and is more distant from English. German is even bigger, and even more distant. All these languages belong to the same West Germanic family as English.
+
+Many other people came to England later at different times, speaking different languages, and these languages added more words to make today's English. For example, around 800 AD, many Danish and Norse pirates, also called Vikings, came to the country, established Danelaw. So, English got many Norse loanwords. Their languages were Germanic languages, like Old English, but are a little different. They are called the North Germanic languages.
+
+When William the Conqueror took over England in 1066 AD, he brought his nobles, who spoke Norman, a language closely related to French. English changed a lot because it was mostly being spoken instead of written for about 300 years, because all official documents were written in Norman French. English borrowed many words from Norman at that time, and also began to drop the old word endings. English of this time is called Middle English. Geoffrey Chaucer is a well known writer of Middle English. After more sound changes, Middle English became Modern English.
+
+English continued to take new words from other languages, for example mainly from French (around 30% to 40% of its words), but also Chinese, Hindi and Urdu, Japanese, Dutch, Spanish, Portuguese, etc. Because scientists from different countries needed to talk to one another, they chose names for scientific things in the languages they all knew: Greek and Latin. Those words came to English also, for example, photography ("photo-" means "light" and "-graph" means "picture" or "writing", in Greek.[7] A photograph is a picture made using light), or telephone. So, English is made of Old English, Danish, Norse, and French, and has been changed by Latin, Greek, Chinese, Hindi, Japanese, Dutch and Spanish, and some words from other languages.
+
+English grammar has also changed, becoming simpler and less Germanic. The classic example is the loss of case in grammar. Grammatical case shows the role of a noun, adjective or pronoun in a sentence. In Latin (and other Indo-European languages) this is done by adding suffixes, but English usually does not. The style of English is that meaning is made clear more by context and syntax.
+
+The history of the British Empire has added to the spread of English. English is an important language in many places today. In Australia, Canada, India, Pakistan, South Africa, and the United States, among others (like those in the Commonwealth of Nations), English is the main language. Because the United Kingdom (the country where England is) and the United States have historically been powerful in commerce and government, many people find it helpful to learn English to communicate in science, business, and diplomacy. This is called learning English as an additional language, English as a Second Language (ESL) or English as a Foreign Language (EFL).
+
+English literature has many famous stories and plays. William Shakespeare was a famous English writer of poems and plays. His English is Early Modern English, and not quite like what people speak or write today. Early Modern English sounded different, partly because the language was beginning a "great vowel shift". Later, many short stories and novels also used English. The novel as we know it is first seen in 18th century English.[8] Today, many famous songs and movies (cinema films) use the English language.
+
+Written English uses a strange spelling. Different words can use the same letters and combinations for very different sounds. For example, "-ough" was once a guttural but has become different in "through" (threw), "rough" (ruff), "dough" (doe) or "cough" (coff). This can make it a difficult language to learn.[9]
+
+Many English speaking countries spell words differently. In the United States, some words are spelled differently from the way they are spelled in the United Kingdom and many other countries (such as those of the British Commonwealth) where English is the main language. These different ways of spelling are sometimes called "American English" and "British English". For example, "colour" is spelled "color" in the USA, and "programme" is spelled "program" in the USA. Even the word "spelled" is different in British English, where it is "spelt".
+
+Nearly 60% of the vocabulary in the English language comes from Latin and Neo-Latin languages (mainly French):
+
+However, in the most common words, the amount of Germanic origin words is much higher.
+Also, besides the simple vocabulary, there are expressions and typical short phrases, many of which are of Germanic origin.

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+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

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+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2452.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2453.html.txt

@@ -0,0 +1,55 @@
+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/2454.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2455.html.txt

@@ -0,0 +1,55 @@
+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/2456.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2457.html.txt

@@ -0,0 +1,55 @@
+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/2458.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2459.html.txt

@@ -0,0 +1,55 @@
+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/246.html.txt

@@ -0,0 +1,19 @@
+Angola, (/ænˈɡoʊlə/), officially the Republic of Angola, is a country in southern Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city.
+
+Angola is a member state of the African Union, the Community of Portuguese Language Countries, the Latin Union, South Atlantic Peace and Cooperation Zone and the Southern African Development Community.
+
+Portugal built up its power in Angola from the late 15th to the middle 20th century.
+
+After independence there was a civil war from 1975 to 2002. Cuba and the Soviet Bloc supported the ruling People's Movement for the Liberation of Angola (MPLA). South Africa supported the insurgent anti-communist National Union for the Total Independence of Angola (UNITA). The war ended after the rebel leader was killed.
+
+Angola is the world's twenty-third largest country. Angola is bordered by Namibia to the south, Zambia to the east, the Democratic Republic of the Congo to the north-east, and the South Atlantic Ocean to the west.
+
+Angola's average temperature on the coast is 16 °C (61 °F) in the winter and 21 °C (70 °F) in the summer. It has two seasons; dry (May to October) and hot rainy (November to April).
+
+Angola had a population of 25,789,024 in 2014.[2]
+
+Map of Angola with provinces numbered.
+
+Angola is divided into eighteen provinces.
+
+See List of settlements in Angola for the cities and towns in the country.

ensimple/2460.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2461.html.txt

@@ -0,0 +1,55 @@
+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/2462.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2463.html.txt

@@ -0,0 +1,55 @@
+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/2464.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2465.html.txt

@@ -0,0 +1,55 @@
+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

ensimple/2466.html.txt

@@ -0,0 +1,25 @@
+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

ensimple/2467.html.txt

@@ -0,0 +1,55 @@
+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

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+An extrasolar planet (or exoplanet) is a natural planet in a planetary system outside our own solar system.
+
+In 2013, estimates of the number of terrestrial planets in the Milky Way ranged from at least 17 billion[1] to at least 144 billion.[2] The smaller estimate studied planet candidates gathered by the Kepler space observatory.[3] Among them are 461 Earth-size planets, at least four of which are in the "habitable zone" where liquid water can exist. One of the four, dubbed Kepler-69c, is a mere 1.5 times the size of the Earth and around a star like our own Sun – about as near as the current data allow to finding an "Earth 2.0".[4]
+
+Earlier work suggested that there are at least 100 billion planets of all types in our galaxy, an average of at least one per star. There are also planets that orbit brown dwarfs, and free-floating planets that orbit the galaxy directly just as the stars do. It is unclear whether either type should be called a "planet".[5][6][7]
+
+In the sixteenth century, the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. Bruno was burnt at the stake by the Holy Inquisition.[8]
+
+In the eighteenth century, the same possibility was mentioned by Isaac Newton in his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centres of similar systems, they will all be constructed according to a similar design and subject to the dominion of One".[9]
+
+The first published and confirmed discovery was made in 1988.[10] It was finally confirmed in 1992.
+
+In 1992, radio astronomers announced the discovery of planets around another pulsar.[11] These pulsar planets are believed to have formed from the unusual remnants of the supernova that produced the pulsar, in a second round of planet formation. Otherwise they may be the remaining rocky cores of gas giants that survived the supernova and then decayed into their current orbits.
+
+On October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[12] This discovery, made at the Observatoire de Haute-Provence, started the modern era of exoplanetary discovery. Technological advances, most notably in high-resolution spectroscopy, led to the quick detection of many new exoplanets. These advances allowed astronomers to detect exoplanets indirectly by measuring their gravitational influence on the motion of their parent stars. Additional extrasolar planets were eventually detected by watching occultations when a star becomes dimmer as an orbiting planet passed in front of it.
+
+In May 2016 NASA announced the discovery of 1,284 exoplanets which brought the total number of exoplanets to over 3,000.[13]
+
+Extrasolar planets can have many different forms.
+
+
+
+The nearest star with planets is Alpha Centauri. It is 4.3 light years away. Using standard rockets, it would take tens of thousands of years to get there.[14]  The nearest star similar to our Sun is Tau Ceti. It has five planets, one of which in the habitable zone, where liquid water may exist.[15][16]
+
+Some extrasolar planets might be Earth-like. This means that they have conditions very similar to that of the Earth. Planets are ranked by a formula called the Earth similarity index or ESI for short. The ESI goes from one (most Earth-like) to zero (least Earth-like). For a planet to be habitable it should have an ESI of at least 0.8.[17] For comparison, the four solar terrestrial planets are included in this list.

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+A star is a very large ball of bright glowing hot matter in space. That matter is called plasma. Stars are held together by gravity. They give out heat and light because they are very hot.
+
+Stars are hot because nuclear reactions happen inside them. Those reactions are called nuclear fusion.  Nuclear fusion makes light and heat and makes bigger and bigger chemical elements. Stars have a lot of hydrogen. Nuclear fusion changes hydrogen into helium. When a star gets old, it starts to change the helium into other bigger chemical elements, like carbon and oxygen. Fusion makes a lot of energy. The energy makes the star very hot. The energy produced by stars moves (radiates) away from them. Much of the energy leaves as light. The rest leaves as other kinds of electromagnetic radiation.
+
+The star nearest to Earth is the Sun. The energy from the Sun supports almost all life on Earth by providing light for plants. Plants turn the light into energy in a process called photosynthesis.[1] The energy from the Sun also causes weather and humidity on Earth.
+
+We can see other stars in the night sky when the Sun goes down. Like the Sun, they are made mostly of hydrogen and a little bit of helium plus other elements. Astronomers often compare those other stars to the Sun. For example, their mass is given in solar masses. A small star may be 0.2 solar masses, a big one 4.0 solar masses.
+
+The Earth and other planets move around (orbit) the Sun. The Sun and all things that orbit the Sun are called the Solar System. Many other stars have planets orbiting them: those planets are called exoplanets. If you were on an exoplanet, our Sun would look like a star in the sky, but you could not see the Earth because it would be too far away.
+
+Proxima Centauri is the star that is closest to our Sun. It is 39.9 trillion kilometres away. This is 4.2 light years away. This means that light from Proxima Centauri takes 4.2 years to reach Earth.
+
+Astronomers think there is a very large number of stars in the Universe. The observable Universe contains more than 2 trillion (1012) galaxies[2] and, overall, as many as an estimated 1×1024 stars[3][4] (more stars than all the grains of sand on planet Earth).[5] That is, 1,000,000,000,000,000,000,000,000 stars, which is many times more than the few hundred billion stars in the Milky Way (our galaxy).
+
+Most stars are very old. They are usually thought to be between 1 billion and 10 billion years old. The oldest stars are 13.7 billion years old. That is as old as the Universe. Some young stars are only a few million years old. Young stars are mostly brighter than old ones.
+
+Stars are different sizes. The smallest stars are neutron stars, which are actually dead stars. They are no bigger than a city. A neutron star has a large amount of mass in a very small space.
+
+Hypergiant stars are the largest stars in the Universe. They have a diameter over 1,500 times bigger than the Sun. If the Sun was a hypergiant star, it would reach out to as far as Jupiter.
+
+The star Betelgeuse is a red supergiant star. Although these stars are very large, they also have low density.
+
+Some stars look brighter than other stars. This difference is measured in terms of apparent magnitude. There are two reasons why stars have different apparent magnitude. If a star is very close to us it will appear much brighter. This is just like a candle. A candle that is close to us appears brighter. The other reason a star can appear brighter is that it is hotter than another cooler star.
+
+Stars give off light but also give off a solar wind and neutrinos. These are very small particles of matter.
+
+Stars are made of mass and mass makes gravity. Gravity makes planets orbit stars. This is why the Earth orbits the Sun. The gravity of two stars can make them go around each other. Stars that orbit each other are called binary stars. Scientists think there are many binary stars. There are even groups of three or more stars that orbit each other. Proxima Centauri is a small star that orbits other stars.
+
+Stars are not spread evenly across all of space. They are grouped into galaxies. A galaxy contains hundreds of billions of stars.
+
+Stars have been important to people all over the world for all of history. Stars have been part of religious practices. Long ago, people believed that stars could never die.
+
+Astronomers organized stars into groups called constellations. They used the constellations to help them see the motion of the planets and to guess the position of the Sun.[6] The motion of the Sun and the stars was used to make calendars. The calendars were used by farmers to decide when to plant crops and when to harvest them.[8]
+
+Stars are made in nebulae. These are areas that have more gas than normal space. The gas in a nebula is pulled together by gravity. The Orion nebula is an example of a place where gas is coming together to form stars.
+
+Stars spend most of their lives combining (fusing) hydrogen with hydrogen to make energy. When hydrogen is fused it makes helium and it makes a lot of energy. To fuse hydrogen into helium it must be very hot and the pressure must be very high. Fusion happens at the center of stars, called "the core".
+
+The smallest stars (red dwarfs) fuse their hydrogen slowly and live for 100 billion years. Red dwarfs live longer than any other type of star. At the end of their lives, they become dimmer and dimmer. Red dwarfs do not explode.
+
+When very heavy stars die, they explode. This explosion is called a supernova. When a supernova happens in a nebula, the explosion pushes the gas in the nebula together. This makes the gas in the nebula very thick (dense). Gravity and exploding stars both help to bring the gas together to make new stars in nebulas.
+
+Most stars use up the hydrogen at their core. When they do, their core becomes smaller and becomes hotter. It becomes so hot it pushes away the outer part of the star. The outer part expands and it makes a red giant star. Astro-physicists think that in about 5 billion years, the Sun will be a red giant. Our Sun will be so large it will eat the Earth. After our Sun stops using hydrogen to make energy, it will use helium in its very hot core. It will be hotter than when it was fusing hydrogen. Heavy stars will also make elements heavier than helium. As a star makes heavier and heavier elements, it makes less and less energy. Iron is a heavy element made in heavy stars.
+
+Our star is an average star. Average stars will push away their outer gases. The gas it pushes away makes a cloud called a planetary nebula. The core part of the star will remain. It will be a ball as big as the Earth and called a white dwarf. It will fade into a black dwarf over a very long time.
+
+Later in large stars,  heavier elements are made by fusion. Finally the star makes a supernova explosion. Most things happen in the universe so slowly we do not notice. But supernova explosions happen in only 100 seconds. When a supernova explodes its flash is as bright as a 100 billion stars. The dying star is so bright it can be seen during the day. Supernova means "new star" because people used to think it was the beginning of a new star. Today we know that a supernova is the death of an old star. The gas of the star is pushed away by the explosion. It forms a giant cloud of gas called a planetary nebula. The crab nebula is a good example. All that remains is a neutron star. If the star was very heavy, the star will make a black hole. Gravity in a black hole is extremely strong. It is so strong that even light cannot escape from a black hole.
+
+The heaviest elements are made in the explosion of a supernova. After billions of years of floating in space, the gas and dust come together to make new stars and new planets.  Much of the gas and dust in space comes from supernovae. Our Sun, the Earth, and all living things are made from star dust.
+
+Astronomers have known for centuries that stars have different colors. When looking at an electromagnetic spectrum, ultraviolet waves are the shortest, and infrared are the longest.[9]   The visible spectrum has wavelengths between these two extremes.
+
+Modern instruments can measure very precisely the color of a star.  This allows astronomers to determine that star's temperature, because a hotter star's black-body radiation has shorter wavelengths.  The hottest stars are blue and violet, then white, then yellow, and the coolest are red.[10] Knowing the color and absolute magnitude, astronomers can place the star on the Hertzsprung-Russell diagram, and estimate its habitable zone and other facts about it.
+
+For example, our Sun is white, and the Earth is the perfect distance away for life. If our Sun was a hotter, blue star, however, Earth would have to be much farther away or else it would be too hot to have water and sustain life.

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+A metre (US spelling, meter) is the basic unit of length in the SI measurement system. The symbol for the metre is m. The first meaning (in the French Revolution) was one ten-millionth of the distance between the Earth's equator and the North Pole along the Paris meridian.[1] The metre is now defined as the distance light travels in a vacuum in 1/299,792,458 of a second.[1]
+
+In the imperial system of measurement, one yard is 0.9144 metres (after international agreement in 1959), so a metre is very close to 39.37 inches: about 3.281 feet, or 1.0936 yards.
+
+*Note: units in bold are the most commonly used.