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= = = Chemical composition = = =

= = = Chemical composition = = =

= = = Chemical composition = = =

When stars form in the present Milky Way galaxy they are composed of about 71 % hydrogen and 27 % helium , as measured by mass , with a small fraction of heavier elements . Typically the portion of heavy elements is measured in terms of the iron content of the stellar atmosphere , as iron is a common element and its absorption lines are relatively easy to measure . The portion of heavier elements may be an indicator of the likelihood that the star has a planetary system .

When stars form in the present Milky Way galaxy they are composed of about 71 % hydrogen and 27 % helium , as measured by mass , with a small fraction of heavier elements . Typically the portion of heavy elements is measured in terms of the iron content of the stellar atmosphere , as iron <a href='drop_aux' title='1'><mark>is</mark></a>a common element and its absorption lines <a href='drop_aux' title='2'><mark>are</mark></a>relatively easy to measure . The portion of heavier elements may be an indicator of the likelihood that the star <a href='got' title='3'><mark>has</mark></a> a planetary system .

When stars form in da present Milky Way galaxy they r composed of about 71 % hydrogen and 27 % helium , as measured by mass , wid a small fraction of heavier elements . Typically the portion of heavy elements is measured in terms of the iron content of the stellar atmosphere , as iron a common element and its absorption lines relatively easy to measure . The portion of heavier elements may be an indicator of the likelihood that the star got a planetary system .

The star with the lowest iron content ever measured is the dwarf HE1327 @-@ 2326 , with only 1 / 200,000th the iron content of the Sun . By contrast , the super @-@ metal @-@ rich star μ Leonis has nearly double the abundance of iron as the Sun , while the planet @-@ bearing star 14 Herculis has nearly triple the iron . There also exist chemically peculiar stars that show unusual abundances of certain elements in their spectrum ; especially chromium and rare earth elements . Stars with cooler outer atmospheres , including the Sun , can form various diatomic and polyatomic molecules .

The star with the lowest iron content ever measured <a href='drop_aux' title='1'><mark>is</mark></a>the dwarf HE1327 @-@ 2326 , with only 1 / 200,000th the iron content of the Sun . By contrast , the super @-@ metal @-@ rich star μ Leonis <a href='got' title='2'><mark>has</mark></a> nearly double the abundance of iron as the Sun , while the planet @-@ bearing star 14 Herculis <a href='got' title='3'><mark>has</mark></a> nearly triple the iron . <a href='dey_it' title='4'><mark>There</mark></a> also exist chemically peculiar stars <a href='null_relcl' title='5'><mark>that</mark></a>show unusual abundances of certain elements in their spectrum ; especially chromium and rare earth elements . Stars with cooler outer atmospheres , including the Sun , can form various diatomic and polyatomic molecules .

The star with da lowest iron content eva measured the dwarf HE1327 @-@ 2326 , with only 1 / 200,000th the iron content of the Sun . By contrast , the super @-@ metal @-@ rich star μ Leonis got nearly double tdaabundance of iron as thdaun , while the planet @-@ bearing star 14 Herculis got nearly triple the iron . It also exist chemically peculiar stars show unusual abundances of certain elements in their spectrum ; especially chromium and rare earth elements . Stars wit cooler outer atmospheres , including thedan , can form various diatomic and polyatomic molecules .

= = = Diameter = = =

= = = Diameter = = =

= = = Diameter = = =

Due to their great distance from the Earth , all stars except the Sun appear to the unaided eye as shining points in the night sky that twinkle because of the effect of the Earth 's atmosphere . The Sun is also a star , but it is close enough to the Earth to appear as a disk instead , and to provide daylight . Other than the Sun , the star with the largest apparent size is R Doradus , with an angular diameter of only 0 @.@ 057 arcseconds .

Due to their great distance from the Earth , all stars except the Sun appear to the unaided eye as shining points in the night sky <a href='null_relcl' title='1'><mark>that</mark></a>twinkle because of the effect of the Earth <a href='null_genetive' title='2'><mark>'s</mark></a>atmosphere . The Sun <a href='drop_aux' title='3'><mark>is</mark></a>also a star , but it <a href='drop_aux' title='4'><mark>is</mark></a>close enough to the Earth to appear as a disk instead , and to provide daylight . Other than the Sun , the star with the largest apparent size <a href='drop_aux' title='5'><mark>is</mark></a>R Doradus , with an angular diameter of only 0 @.@ 057 arcseconds .

Due to their great distance from the Earth , alll stars except da Sun appear to the unaided eye as shining points in the night sky twinkle becuz of tdaeffect of thdaarth atmosphere . Thedan also a star , but it close enough to the dath to appear as a disk instead , and to provide daylight . Other than the Sun , the star with the ldaest apparent size R Doradus , with an angular diameter of only 0 @.@ 057 arcseconds .

The disks of most stars are much too small in angular size to be observed with current ground @-@ based optical telescopes , and so interferometer telescopes are required to produce images of these objects . Another technique for measuring the angular size of stars is through occultation . By precisely measuring the drop in brightness of a star as it is occulted by the Moon ( or the rise in brightness when it reappears ) , the star 's angular diameter can be computed .

The disks of most stars <a href='drop_aux' title='1'><mark>are</mark></a>much too small in angular size to be observed with current ground @-@ based optical telescopes , and so interferometer telescopes are required to produce images of these objects . Another technique for measuring the angular size of stars is through occultation . By precisely measuring the drop in brightness of a star as it is occulted by the Moon ( or the rise in brightness when it <a href='uninflect' title='2'><mark>reappears</mark></a> ) , the star <a href='null_genetive' title='3'><mark>'s</mark></a>angular diameter can be computed .

The disks of most stars much too small in angular size to b observed witt current ground @-@ based optical telescopes , and soo interferometer telescopes are required to produce images of these objects . Another technique for measuring da angular size of stars is through occultation . By precisely measuring the drop in brightness of a star as it is occulted by the Moon ( or the rise in brightness when it reappear ) , the star angular diameter can be computed .

Stars range in size from neutron stars , which vary anywhere from 20 to 40 km ( 25 mi ) in diameter , to supergiants like Betelgeuse in the Orion constellation , which has a diameter approximately 1 @,@ 070 times that of the Sun — about 1 @,@ 490 @,@ 171 @,@ 880 km ( 925 @,@ 949 @,@ 878 mi ) . Betelgeuse , however , has a much lower density than the Sun .

Stars range in size from neutron stars , which vary anywhere from 20 to 40 km ( 25 mi ) in diameter , to supergiants like Betelgeuse in the Orion constellation , which <a href='got' title='1'><mark>has</mark></a> a diameter approximately 1 @,@ 070 times <a href='null_relcl' title='2'><mark>that</mark></a>of the Sun — about 1 @,@ 490 @,@ 171 @,@ 880 km ( 925 @,@ 949 @,@ 878 mi ) . Betelgeuse , however , <a href='got' title='3'><mark>has</mark></a> a much lower density than the Sun .

Stars range in size from neutron stars , which vary anywhere from 20 to 40 km ( 25 mi ) in diameter , to supergiants like Betelgeuse in the Orion constellation , which got a diameter approximately 1 @,@ 070 times of da Sun — about 1 @,@ 490 @,@ 171 @,@ 880 km ( 925 @,@ 949 @,@ 878 mi ) . Betelgeuse , however , got a much lower density den tdaSun .

= = = Kinematics = = =

= = = Kinematics = = =

= = = Kinematics = = =

The motion of a star relative to the Sun can provide useful information about the origin and age of a star , as well as the structure and evolution of the surrounding galaxy . The components of motion of a star consist of the radial velocity toward or away from the Sun , and the traverse angular movement , which is called its proper motion .

The motion of a star relative to the Sun can provide useful information about the origin and age of a star , as well as the structure and evolution of the surrounding galaxy . The components of motion of a star consist of the radial velocity toward or away from the Sun , and the traverse angular movement , which is called its proper motion .

The motion of a star relative to da Sun can provide useful information about tdaorigin and age of a star , as well as the structure and evolution of the surrounding galaxy . The components of motion of a star consist of the radial velocity toward or away from the Sun , and the traverse angular movement , which is called its proper motion .

Radial velocity is measured by the doppler shift of the star 's spectral lines , and is given in units of km / s . The proper motion of a star , its parallax , is determined by precise astrometric measurements in units of milli @-@ arc seconds ( mas ) per year . With knowledge of the star 's parallax and its distance , the proper motion velocity can be calculated . Together with the radial velocity , the total velocity can be calculated . Stars with high rates of proper motion are likely to be relatively close to the Sun , making them good candidates for parallax measurements .

Radial velocity is measured by the doppler shift of the star <a href='null_genetive' title='1'><mark>'s</mark></a>spectral lines , and is given in units of km / s . The proper motion of a star , its parallax , is determined by precise astrometric measurements in units of milli @-@ arc seconds ( mas ) per year . With knowledge of the star <a href='null_genetive' title='2'><mark>'s</mark></a>parallax and its distance , the proper motion velocity can be calculated . Together with the radial velocity , the total velocity can be calculated . Stars with high rates of proper motion <a href='drop_aux' title='3'><mark>are</mark></a>likely to be relatively close to the Sun , making them good candidates for parallax measurements .

Radial velocity is measured by da doppler shift of the star spectral lines , and is given in units of km / s . The proper motion of a star , its parallax , is determined by precise astrometric measurements in units of milli @-@ arc secs ( mas ) per year . With knowledge of tdastar parallax and its distance , thdaroper motion velocity can be calculated . Together wid the radial velocity , thedatal velocity can be calculated . Stars with high rates of proper motion likely to b relatively close to the da , making em gud candidates fir parallax measurements .

When both rates of movement are known , the space velocity of the star relative to the Sun or the galaxy can be computed . Among nearby stars , it has been found that younger population I stars have generally lower velocities than older , population II stars . The latter have elliptical orbits that are inclined to the plane of the galaxy . A comparison of the kinematics of nearby stars has allowed astronomers to trace their origin to common points in giant molecular clouds , and are referred to as stellar associations .

When both rates of movement are known , the space velocity of the star relative to the Sun or the galaxy can be computed . Among nearby stars , it <a href='been_done' title='1'><mark>has</mark></a> been found that younger population I <a href='uninflect' title='2'><mark>stars</mark></a> have generally lower velocities than older , population II stars . The latter <a href='got' title='3'><mark>have</mark></a> elliptical orbits <a href='null_relcl' title='4'><mark>that</mark></a><a href='drop_aux' title='5'><mark>are</mark></a>inclined to the plane of the galaxy . A comparison of the kinematics of nearby stars <a href='been_done' title='6'><mark>has</mark></a> allowed astronomers to trace their origin to common points in giant molecular clouds , and are referred to as stellar associations .

When both rates of movement r known , da space velocity of tdastar relative to the Sun or thdaalaxy can b computed . Among nearby stars , it done been found that younger population I star have generally lower velocities than older , population II stars . The latter got elliptical orbits inclined to the plane of thedalaxy . A comparison of the kinematics of nearby stars done allowed astronomers to trace their origin to common points in giant molecular clouds , and are referred to as stellar associations .

= = = Magnetic field = = =

= = = Magnetic field = = =

= = = Magnetic field = = =

The magnetic field of a star is generated within regions of the interior where convective circulation occurs . This movement of conductive plasma functions like a dynamo , wherein the movement of elecrical charges induce magnetic fields , as does a mechanical dynamo . Those magnetic fields have a great range that extend throughout and beyond the star . The strength of the magnetic field varies with the mass and composition of the star , and the amount of magnetic surface activity depends upon the star 's rate of rotation . This surface activity produces starspots , which are regions of strong magnetic fields and lower than normal surface temperatures . Coronal loops are arching magnetic field flux lines that rise from a star 's surface into the star 's outer atmosphere , its corona . The coronal loops can be seen due to the plasma they conduct along their length . Stellar flares are bursts of high @-@ energy particles that are emitted due to the same magnetic activity .

The magnetic field of a star is generated within regions of the interior where convective circulation <a href='uninflect' title='1'><mark>occurs</mark></a> . This movement of conductive plasma functions like a dynamo , wherein the movement of elecrical charges induce magnetic fields , as <a href='uninflect' title='2'><mark>does</mark></a> a mechanical dynamo . Those magnetic fields <a href='got' title='3'><mark>have</mark></a> a great range <a href='null_relcl' title='4'><mark>that</mark></a>extend throughout and beyond the star . The strength of the magnetic field <a href='uninflect' title='5'><mark>varies</mark></a> with the mass and composition of the star , and the amount of magnetic surface activity <a href='uninflect' title='6'><mark>depends</mark></a> upon the star <a href='null_genetive' title='7'><mark>'s</mark></a>rate of rotation . This surface activity <a href='uninflect' title='8'><mark>produces</mark></a> starspots , which <a href='drop_aux' title='9'><mark>are</mark></a>regions of strong magnetic fields and lower than normal surface temperatures . Coronal loops are arching magnetic field flux lines <a href='null_relcl' title='10'><mark>that</mark></a>rise from a star <a href='null_genetive' title='11'><mark>'s</mark></a>surface into the star <a href='null_genetive' title='12'><mark>'s</mark></a>outer atmosphere , its corona . The coronal loops can be seen due to the plasma they conduct along their length . Stellar flares <a href='drop_aux' title='13'><mark>are</mark></a>bursts of high @-@ energy particles <a href='null_relcl' title='14'><mark>that</mark></a>are emitted due to the same magnetic activity .

Da magnetic field of a star is generated within regions of the interior where convective circulation occur . This movement of conductive plasma functions like a dynamo , wherein the movement of elecrical charges induce magnetic fields , as do a mechanical dynamo . Those magnetic fields got a great range extend throughout and beyond the star . The strength of the magnetic field vary with the mass and composition of tdastar , and thdamount of magnetic surface activity depend upon thedaar rate of rotation . This surface activity produce starspots , which regions of strong magnetic fields and lower den normal surface temperatures . Coronal loops r arching magnetic field flux lines rise from a star surface into the dar outer atmosphere , its corona . The coronal loops can b seen due to the pdama they conduct along their length . Stellar flares bursts of high @-@ energy particles are emitted due to the same magnetic activity .

Young , rapidly rotating stars tend to have high levels of surface activity because of their magnetic field . The magnetic field can act upon a star 's stellar wind , functioning as a brake to gradually slow the rate of rotation with time . Thus , older stars such as the Sun have a much slower rate of rotation and a lower level of surface activity . The activity levels of slowly rotating stars tend to vary in a cyclical manner and can shut down altogether for periods of time . During the Maunder minimum , for example , the Sun underwent a 70 @-@ year period with almost no sunspot activity .

Young , rapidly rotating stars tend to have high levels of surface activity because of their magnetic field . The magnetic field can act upon a star <a href='null_genetive' title='1'><mark>'s</mark></a>stellar wind , functioning as a brake to gradually slow the rate of rotation with time . Thus , older stars such as the Sun <a href='got' title='2'><mark>have</mark></a> a much slower rate of rotation and a lower level of surface activity . The activity levels of slowly rotating stars tend to vary in a cyclical manner and can shut down altogether for periods of time . During the Maunder minimum , for example , the Sun underwent a 70 @-@ year period with almost no sunspot activity .

Young , rapidly rotating stars tend to have high levels of surface activity because of their magnetic field . The magnetic field can act upon a star stellar wind , functioning as a brake to gradually slow the rate of rotation with time . Thus , older stars such as da Sun got a much slower rate of rotation and a lower level of surface activity . The activity levels of slowly rotating stars tend to vary in a cyclical manner and can shut down altogether for periods of time . During the Maunder minimum , fir example , the Sun underwent a 70 @-@ year period with almost no sunspot activity .

= = = Mass = = =

= = = Mass = = =

= = = Mass = = =

One of the most massive stars known is Eta Carinae , which , with 100 – 150 times as much mass as the Sun , will have a lifespan of only several million years . Studies of the most massive open clusters suggests 150 M ☉ as an upper limit for stars in the current era of the universe . This represents an empirical value for the theoretical limit on the mass of forming stars due to increasing radiation pressure on the accreting gas cloud . Several stars in the R136 cluster in the Large Magellanic Cloud have been measured with larger masses , but it has been determined that they could have been created through the collision and merger of massive stars in close binary systems , sidestepping the 150 M ☉ limit on massive star formation .

One of the most massive stars known is Eta Carinae , which , with 100 – 150 times as much mass as the Sun , will have a lifespan of only several million years . Studies of the most massive open clusters <a href='uninflect' title='1'><mark>suggests</mark></a> 150 M ☉ as an upper limit for stars in the current era of the universe . This <a href='uninflect' title='2'><mark>represents</mark></a> an empirical value for the theoretical limit on the mass of forming stars due to increasing radiation pressure on the accreting gas cloud . Several stars in the R136 cluster in the Large Magellanic Cloud <a href='been_done' title='3'><mark>have</mark></a> been measured with larger masses , but it <a href='been_done' title='4'><mark>has</mark></a> been determined that they could <a href='been_done' title='5'><mark>have</mark></a> been created through the collision and merger of massive stars in close binary systems , sidestepping the 150 M ☉ limit on massive star formation .

One of the most massive stars known is Eta Carinae , which , with 100 – 150 times as much mass as the Sun , will have a lifespan of only several million years . Studies of the most massive open clusters suggest 150 M ☉ as an upper limit fa stars in the current era of the universe . dis represent an empirical value for the theoretical limit on the mass of forming stars due to increasing radiation pressure on the accreting gas cloud . Several stars in the R136 cluster in da Large Magellanic Cloud done been measured with larger masses , but it done been determined dat they could done been created through tdacollision and merger of massive stars in close binary systems , sidestepping the 150 M ☉ limit on massive star formation .

The first stars to form after the Big Bang may have been larger , up to 300 M ☉ , due to the complete absence of elements heavier than lithium in their composition . This generation of supermassive population III stars is likely to have existed in the very early universe ( i.e. , they are observed to have a high redshift ) , and may have started the production of chemical elements heavier than hydrogen that are needed for the later formation of planets and life . In June 2015 , astronomers reported evidence for Population III stars in the Cosmos Redshift 7 galaxy at z = 6 @.@ 60 .

The first stars to form after the Big Bang may have been larger , up to 300 M ☉ , due to the complete absence of elements heavier than lithium in their composition . This generation of supermassive population III stars <a href='drop_aux' title='1'><mark>is</mark></a>likely to <a href='been_done' title='2'><mark>have</mark></a> existed in the very early universe ( i.e. , they are observed to have a high redshift ) , and may <a href='been_done' title='3'><mark>have</mark></a> started the production of chemical elements heavier than hydrogen <a href='null_relcl' title='4'><mark>that</mark></a>are needed for the later formation of planets and life . In June 2015 , astronomers reported evidence for Population III stars in the Cosmos Redshift 7 galaxy at z = 6 @.@ 60 .

The first stars to form after the Big Bang may have been larger , up to 300 M ☉ , due to da complete absence of elements heavier den lithium in their composition . dis generation of supermassive population III stars likely to done existed in tdavery early universe ( i.e. , they are observed to have a high redshift ) , and may done started the production of chemical elements heavier tdenhydrogen are needed fir the later formation of planets and life . In June 2015 , astronomers reported evidence for Population III stars in thdaosmos Redshift 7 galaxy at z = 6 @.@ 60 .

With a mass only 80 times that of Jupiter ( MJ ) , 2MASS J0523 @-@ 1403 is the smallest known star undergoing nuclear fusion in its core . For stars with metallicity similar to the Sun , the theoretical minimum mass the star can have and still undergo fusion at the core , is estimated to be about 75 MJ . When the metallicity is very low , however , the minimum star size seems to be about 8 @.@ 3 % of the solar mass , or about 87 MJ . Smaller bodies called brown dwarfs , occupy a poorly defined grey area between stars and gas giants .

With a mass only 80 times that of Jupiter ( MJ ) , 2MASS J0523 @-@ 1403 <a href='drop_aux' title='1'><mark>is</mark></a>the smallest known star undergoing nuclear fusion in its core . For stars with metallicity similar to the Sun , the theoretical minimum mass the star can have and still undergo fusion at the core , is estimated to be about 75 MJ . When the metallicity <a href='drop_aux' title='2'><mark>is</mark></a>very low , however , the minimum star size <a href='uninflect' title='3'><mark>seems</mark></a> to be about 8 @.@ 3 % of the solar mass , or about 87 MJ . Smaller bodies called brown dwarfs , occupy a poorly defined grey area between stars and gas giants .

Wid a mass only 80 times that of Jupiter ( MJ ) , 2MASS J0523 @-@ 1403 the smallest known star undergoing nuclear fusion in its core . fir stars with metallicity similar to the Sun , the theoretical minimum mass the star can have and still undergo fusion at the core , is estimated to b about 75 MJ . When da metallicity very low , however , tdaminimum star size seem to be bout 8 @.@ 3 % of thdaolar mass , or aabt87 MJ . Smaller bodies called brown dwarfs , occupy a poorly defined grey area between stars and gas giants .

The combination of the radius and the mass of a star determines its surface gravity . Giant stars have a much lower surface gravity than do main sequence stars , while the opposite is the case for degenerate , compact stars such as white dwarfs . The surface gravity can influence the appearance of a star 's spectrum , with higher gravity causing a broadening of the absorption lines .

The combination of the radius and the mass of a star <a href='uninflect' title='1'><mark>determines</mark></a> its surface gravity . Giant stars <a href='got' title='2'><mark>have</mark></a> a much lower surface gravity than do main sequence stars , while the opposite <a href='drop_aux' title='3'><mark>is</mark></a>the case for degenerate , compact stars such as white dwarfs . The surface gravity can influence the appearance of a star <a href='null_genetive' title='4'><mark>'s</mark></a>spectrum , with higher gravity causing a broadening of the absorption lines .

Da combination of tdaradius and the mass of a star determine its surface gravity . Giant stars got a much lower surface gravity than do main sequence stars , while thdapposite the case for degenerate , compact stars such as white dwarfs . Thedarface gravity can influence the daearance of a star spectrum , with higher gravity causing a broadening of the adarption lines .

= = = Rotation = = =

= = = Rotation = = =

= = = Rotation = = =

The rotation rate of stars can be determined through spectroscopic measurement , or more exactly determined by tracking their starspots . Young stars can have a rotation greater than 100 km / s at the equator . The B @-@ class star Achernar , for example , has an equatorial velocity of about 225 km / s or greater , causing its equator to be slung outward and giving it an equatorial diameter that is more than 50 % greater than between the poles . This rate of rotation is just below the critical velocity of 300 km / s at which speed the star would break apart . By contrast , the Sun rotates once every 25 – 35 days , with an equatorial velocity of 1 @.@ 994 km / s . A main sequence star 's magnetic field and the stellar wind serve to slow its rotation by a significant amount as it evolves on the main sequence .

The rotation rate of stars can be determined through spectroscopic measurement , or more exactly determined by tracking their starspots . Young stars can have a rotation greater than 100 km / s at the equator . The B @-@ class star Achernar , for example , <a href='got' title='1'><mark>has</mark></a> an equatorial velocity of about 225 km / s or greater , causing its equator to be slung outward and giving it an equatorial diameter <a href='null_relcl' title='2'><mark>that</mark></a><a href='drop_aux' title='3'><mark>is</mark></a>more than 50 % greater than between the poles . This rate of rotation is just below the critical velocity of 300 km / s at which speed the star would break apart . By contrast , the Sun <a href='uninflect' title='4'><mark>rotates</mark></a> once every 25 – 35 days , with an equatorial velocity of 1 @.@ 994 km / s . A main sequence star <a href='null_genetive' title='5'><mark>'s</mark></a>magnetic field and the stellar wind serve to slow its rotation by a significant amount as it <a href='uninflect' title='6'><mark>evolves</mark></a> on the main sequence .

The rotation rate of stars can be determined through spectroscopic measurement , or more exactly determined by tracking their starspots . Young stars can have a rotation greater den 100 km / s at da equator . The B @-@ class star Achernar , fa example , got an equatorial velocity of about 225 km / s or greater , causing its equator to b slung outward and giving it an equatorial diameter more tden50 % greater thdenetween the poles . dis rate of rotation is just below the critical velocity of 300 km / s at which speed the star would break apart . By contrast , tdaSun rotate once every 25 – 35 dayz , with an equatorial velocity of 1 @.@ 994 km / s . A main sequence star magnetic field and thdatellar wind serve to slow its rotation by a significant amount as it evolve on the main sequence .

Degenerate stars have contracted into a compact mass , resulting in a rapid rate of rotation . However they have relatively low rates of rotation compared to what would be expected by conservation of angular momentum — the tendency of a rotating body to compensate for a contraction in size by increasing its rate of spin . A large portion of the star 's angular momentum is dissipated as a result of mass loss through the stellar wind . In spite of this , the rate of rotation for a pulsar can be very rapid . The pulsar at the heart of the Crab nebula , for example , rotates 30 times per second . The rotation rate of the pulsar will gradually slow due to the emission of radiation .

Degenerate stars <a href='been_done' title='1'><mark>have</mark></a> contracted into a compact mass , resulting in a rapid rate of rotation . However they <a href='got' title='2'><mark>have</mark></a> relatively low rates of rotation compared to what would be expected by conservation of angular momentum — the tendency of a rotating body to compensate for a contraction in size by increasing its rate of spin . A large portion of the star <a href='null_genetive' title='3'><mark>'s</mark></a>angular momentum is dissipated as a result of mass loss through the stellar wind . In spite of this , the rate of rotation for a pulsar can be very rapid . The pulsar at the heart of the Crab nebula , for example , <a href='uninflect' title='4'><mark>rotates</mark></a> 30 times per second . The rotation rate of the pulsar will gradually slow due to the emission of radiation .

Degenerate stars done contracted into a compact mass , resulting in a rapid rate of rotation . However they got relatively low rates of rotation compared to what would be expected by conservation of angular momentum — the tendency of a rotating body to compensate fa a contraction in size by increasing its rate of spin . A bigass portion of the star angular momentum is dissipated as a result of mass loss thru da stellar wind . In spite of this , tdarate of rotation ffira pulsar can b very rapid . The pulsar at thdaeart of thedaab nebula , ffaexample , rotate 30 times per second . The rotation rate of the pulsar will gradually slow due to the emission of radiation .

= = = Temperature = = =

= = = Temperature = = =

= = = Temperature = = =

The surface temperature of a main sequence star is determined by the rate of energy production of its core and by its radius , and is often estimated from the star 's color index . The temperature is normally given in terms of an effective temperature , which is the temperature of an idealized black body that radiates its energy at the same luminosity per surface area as the star . Note that the effective temperature is only a representative of the surface , as the temperature increases toward the core . The temperature in the core region of a star is several million kelvins .

The surface temperature of a main sequence star is determined by the rate of energy production of its core and by its radius , and is often estimated from the star <a href='null_genetive' title='1'><mark>'s</mark></a>color index . The temperature is normally given in terms of an effective temperature , which <a href='drop_aux' title='2'><mark>is</mark></a>the temperature of an idealized black body <a href='null_relcl' title='3'><mark>that</mark></a><a href='uninflect' title='4'><mark>radiates</mark></a> its energy at the same luminosity per surface area as the star . Note that the effective temperature is only a representative of the surface , as the temperature <a href='uninflect' title='5'><mark>increases</mark></a> toward the core . The temperature in the core region of a star <a href='drop_aux' title='6'><mark>is</mark></a>several million kelvins .

The surface temperature of a main sequence star is determined by the rate of energy production of its core and by its radius , and is often estimated from da star color index . The temperature is normally given in terms of an effective temperature , which the temperature of an idealized black body radiate its energy at the same luminosity per surface area as the star . Note that the effective temperature is only a representative of the surface , as the temperature increase toward the core . Tdatemperature in the core region of a star several million kelvins .

The stellar temperature will determine the rate of ionization of various elements , resulting in characteristic absorption lines in the spectrum . The surface temperature of a star , along with its visual absolute magnitude and absorption features , is used to classify a star ( see classification below ) .

The stellar temperature will determine the rate of ionization of various elements , resulting in characteristic absorption lines in the spectrum . The surface temperature of a star , along with its visual absolute magnitude and absorption features , is used to classify a star ( see classification below ) .

The stellar temperature gon determine da rate of ionization of various elements , resulting in characteristic absorption lines in the spectrum . The surface temperature of a star , along w its visual absolute magnitude and absorption features , is used to classify a star ( see classification below ) .

Massive main sequence stars can have surface temperatures of 50 @,@ 000 K. Smaller stars such as the Sun have surface temperatures of a few thousand K. Red giants have relatively low surface temperatures of about 3 @,@ 600 K ; but they also have a high luminosity due to their large exterior surface area .

Massive main sequence stars can have surface temperatures of 50 @,@ 000 K. Smaller stars such as the Sun <a href='got' title='1'><mark>have</mark></a> surface temperatures of a few thousand K. Red giants <a href='got' title='2'><mark>have</mark></a> relatively low surface temperatures of about 3 @,@ 600 K ; but they also <a href='got' title='3'><mark>have</mark></a> a high luminosity due to their large exterior surface area .

Massive main sequence stars can have surface temperatures of 50 @,@ 000 K. Smaller stars such as the Sun got surface temperatures of a few thousand K. Red giants got relatively low surface temperatures of abt 3 @,@ 600 K ; but they also got a high luminosity due to their bigass exterior surface area .

= = Radiation = =

= = Radiation = =

= = Radiation = =

The energy produced by stars , a product of nuclear fusion , radiates to space as both electromagnetic radiation and particle radiation . The particle radiation emitted by a star is manifested as the stellar wind , which streams from the outer layers as electrically charged protons and alpha and beta particles . Although almost massless , there also exists a steady stream of neutrinos emanating from the star 's core .

The energy produced by stars , a product of nuclear fusion , <a href='uninflect' title='1'><mark>radiates</mark></a> to space as both electromagnetic radiation and particle radiation . The particle radiation emitted by a star is manifested as the stellar wind , which <a href='uninflect' title='2'><mark>streams</mark></a> from the outer layers as electrically charged protons and alpha and beta particles . Although almost massless , <a href='dey_it' title='3'><mark>there</mark></a> also <a href='uninflect' title='4'><mark>exists</mark></a> a steady stream of neutrinos emanating from the star <a href='null_genetive' title='5'><mark>'s</mark></a>core .

The energy produced by stars , a product of nuclear fusion , radiate to space as both electromagnetic radiation and particle radiation . da particle radiation emitted by a star is manifested as the stellar wind , which stream from tdaouter layers as electrically charged protons and alpha and beta particles . Although almost massless , it also exist a steady stream of neutrinos emanating from the star core .

The production of energy at the core is the reason stars shine so brightly : every time two or more atomic nuclei fuse together to form a single atomic nucleus of a new heavier element , gamma ray photons are released from the nuclear fusion product . This energy is converted to other forms of electromagnetic energy of lower frequency , such as visible light , by the time it reaches the star 's outer layers .

The production of energy at the core <a href='drop_aux' title='1'><mark>is</mark></a>the reason stars shine so brightly : every time two or more atomic nuclei fuse together to form a single atomic nucleus of a new heavier element , gamma ray photons are released from the nuclear fusion product . This energy is converted to other forms of electromagnetic energy of lower frequency , such as visible light , by the time it <a href='uninflect' title='2'><mark>reaches</mark></a> the star <a href='null_genetive' title='3'><mark>'s</mark></a>outer layers .

Da production of energy at the core tdareason stars shine soo brightly : every time two or more atomic nuclei fuse together to form a single atomic nucleus of a new heavier element , gamma ray photons are released from the nuclear fusion product . This energy is converted to other forms of electromagnetic energy of lower frequency , such as visible light , by thdaime it reach the star outer layers .

The color of a star , as determined by the most intense frequency of the visible light , depends on the temperature of the star 's outer layers , including its photosphere . Besides visible light , stars also emit forms of electromagnetic radiation that are invisible to the human eye . In fact , stellar electromagnetic radiation spans the entire electromagnetic spectrum , from the longest wavelengths of radio waves through infrared , visible light , ultraviolet , to the shortest of X @-@ rays , and gamma rays . From the standpoint of total energy emitted by a star , not all components of stellar electromagnetic radiation are significant , but all frequencies provide insight into the star 's physics .

The color of a star , as determined by the most intense frequency of the visible light , <a href='uninflect' title='1'><mark>depends</mark></a> on the temperature of the star <a href='null_genetive' title='2'><mark>'s</mark></a>outer layers , including its photosphere . Besides visible light , stars also emit forms of electromagnetic radiation <a href='null_relcl' title='3'><mark>that</mark></a><a href='drop_aux' title='4'><mark>are</mark></a>invisible to the human eye . In fact , stellar electromagnetic radiation <a href='uninflect' title='5'><mark>spans</mark></a> the entire electromagnetic spectrum , from the longest wavelengths of radio waves through infrared , visible light , ultraviolet , to the shortest of X @-@ rays , and gamma rays . From the standpoint of total energy emitted by a star , not all components of stellar electromagnetic radiation <a href='drop_aux' title='6'><mark>are</mark></a>significant , but all frequencies provide insight into the star <a href='null_genetive' title='7'><mark>'s</mark></a>physics .

Da color of a star , as determined by the most intense frequency of the visible light , depend on tdatemperature of the star outer layers , including its photosphere . Besides visible light , stars also emit forms of electromagnetic radiation invisible to the human eye . In fact , stellar electromagnetic radiation span the entire electromagnetic spectrum , from thdaongest wavelengths of radio waves thru infrared , visible light , ultraviolet , to the shortest of X @-@ rays , and gamma rays . From thedaandpoint of total energy emitted by a star , not all components of stellar electromagnetic radiation significant , but all frequencies provide insight into the star physics .

Using the stellar spectrum , astronomers can also determine the surface temperature , surface gravity , metallicity and rotational velocity of a star . If the distance of the star is found , such as by measuring the parallax , then the luminosity of the star can be derived . The mass , radius , surface gravity , and rotation period can then be estimated based on stellar models . ( Mass can be calculated for stars in binary systems by measuring their orbital velocities and distances . Gravitational microlensing has been used to measure the mass of a single star . ) With these parameters , astronomers can also estimate the age of the star .

Using the stellar spectrum , astronomers can also determine the surface temperature , surface gravity , metallicity and rotational velocity of a star . If the distance of the star is found , such as by measuring the parallax , then the luminosity of the star can be derived . The mass , radius , surface gravity , and rotation period can then be estimated based on stellar models . ( Mass can be calculated for stars in binary systems by measuring their orbital velocities and distances . Gravitational microlensing <a href='been_done' title='1'><mark>has</mark></a> been used to measure the mass of a single star . ) With these parameters , astronomers can also estimate the age of the star .

Using the stellar spectrum , astronomers can also determine the surface temperature , surface gravity , metallicity and rotational velocity of a star . If da distance of tdastar is found , such as by measuring the parallax , then thdauminosity of the star can b derived . The mass , radius , surface gravity , and rotation period can then be estimated based on stellar models . ( Mass can be calculated for stars in binary systems by measuring their orbital velocities and distances . Gravitational microlensing done been used to measure thedass of a single star . ) With these parameters , astronomers can also estimate the da of the sda .

= = = Luminosity = = =

= = = Luminosity = = =

= = = Luminosity = = =

The luminosity of a star is the amount of light and other forms of radiant energy it radiates per unit of time . It has units of power . The luminosity of a star is determined by its radius and surface temperature . Many stars do not radiate uniformly across their entire surface . The rapidly rotating star Vega , for example , has a higher energy flux ( power per unit area ) at its poles than along its equator .

The luminosity of a star <a href='drop_aux' title='1'><mark>is</mark></a>the amount of light and other forms of radiant energy it <a href='uninflect' title='2'><mark>radiates</mark></a> per unit of time . It <a href='got' title='3'><mark>has</mark></a> units of power . The luminosity of a star is determined by its radius and surface temperature . Many stars do not radiate uniformly across their entire surface . The rapidly rotating star Vega , for example , <a href='got' title='4'><mark>has</mark></a> a higher energy flux ( power per unit area ) at its poles than along its equator .

The luminosity of a star the amount of light and other forms of radiant energy it radiate per unit of time . It got units of power . The luminosity of a star is determined by its radius and surface temperature . Many stars do not radiate uniformly across their entire surface . The rapidly rotating star Vega , for example , got a higher energy flux ( power per unit area ) at its poles den along its equator .

Patches of the star 's surface with a lower temperature and luminosity than average are known as starspots . Small , dwarf stars such as our Sun generally have essentially featureless disks with only small starspots . Giant stars have much larger , more obvious starspots , and they also exhibit strong stellar limb darkening . That is , the brightness decreases towards the edge of the stellar disk . Red dwarf flare stars such as UV Ceti may also possess prominent starspot features .

Patches of the star <a href='null_genetive' title='1'><mark>'s</mark></a>surface with a lower temperature and luminosity than average are known as starspots . Small , dwarf stars such as our Sun generally have essentially featureless disks with only small starspots . Giant stars <a href='got' title='2'><mark>have</mark></a> much larger , more obvious starspots , and they also exhibit strong stellar limb darkening . That is , the brightness <a href='uninflect' title='3'><mark>decreases</mark></a> towards the edge of the stellar disk . Red dwarf flare stars such as UV Ceti may also possess prominent starspot features .

Patches of the star surface witt a lower temperature and luminosity than average are known as starspots . Small , dwarf stars such as our Sun generally have essentially featureless disks witt only small starspots . Giant stars got much larger , more obvious starspots , and they also exhibit strong stellar limb darkening . That is , the brightness decrease towards the edge of the stellar disk . Red dwarf flare stars such as UV Ceti may also possess prominent starspot features .

= = = Magnitude = = =

= = = Magnitude = = =

= = = Magnitude = = =

The apparent brightness of a star is expressed in terms of its apparent magnitude . It is a function of the star 's luminosity , its distance from Earth , and the altering of the star 's light as it passes through Earth 's atmosphere . Intrinsic or absolute magnitude is directly related to a star 's luminosity , and is what the apparent magnitude a star would be if the distance between the Earth and the star were 10 parsecs ( 32 @.@ 6 light @-@ years ) .

The apparent brightness of a star is expressed in terms of its apparent magnitude . It <a href='drop_aux' title='1'><mark>is</mark></a>a function of the star <a href='null_genetive' title='2'><mark>'s</mark></a>luminosity , its distance from Earth , and the altering of the star <a href='null_genetive' title='3'><mark>'s</mark></a>light as it <a href='uninflect' title='4'><mark>passes</mark></a> through Earth <a href='null_genetive' title='5'><mark>'s</mark></a>atmosphere . Intrinsic or absolute magnitude is directly related to a star <a href='null_genetive' title='6'><mark>'s</mark></a>luminosity , and is what the apparent magnitude a star would be if the distance between the Earth and the star <a href='uninflect' title='7'><mark>were</mark></a> 10 parsecs ( 32 @.@ 6 light @-@ years ) .

Da apparent brightness of a star is expressed in terms of its apparent magnitude . It a function of the star luminosity , its distance from Earth , and the altering of tdastar light as it pass through Earth atmosphere . Intrinsic or absolute magnitude is directly related to a star luminosity , and is what the apparent magnitude a star would b if thdaistance between thedarth and the star was 10 parsecs ( 32 @.@ 6 light @-@ years ) .

Both the apparent and absolute magnitude scales are logarithmic units : one whole number difference in magnitude is equal to a brightness variation of about 2 @.@ 5 times ( the 5th root of 100 or approximately 2 @.@ 512 ) . This means that a first magnitude star ( + 1 @.@ 00 ) is about 2 @.@ 5 times brighter than a second magnitude ( + 2 @.@ 00 ) star , and about 100 times brighter than a sixth magnitude star ( + 6 @.@ 00 ) . The faintest stars visible to the naked eye under good seeing conditions are about magnitude + 6 .

Both the apparent and absolute magnitude scales <a href='drop_aux' title='1'><mark>are</mark></a>logarithmic units : one whole number difference in magnitude <a href='drop_aux' title='2'><mark>is</mark></a>equal to a brightness variation of about 2 @.@ 5 times ( the 5th root of 100 or approximately 2 @.@ 512 ) . This <a href='uninflect' title='3'><mark>means</mark></a> that a first magnitude star ( + 1 @.@ 00 ) is about 2 @.@ 5 times brighter than a second magnitude ( + 2 @.@ 00 ) star , and about 100 times brighter than a sixth magnitude star ( + 6 @.@ 00 ) . The faintest stars visible to the naked eye under good seeing conditions are about magnitude + 6 .

Both the apparent and absolute magnitude scales logarithmic units : one whole number difference in magnitude equal to a brightness variation of about 2 @.@ 5 times ( da 5th root of 100 or approximately 2 @.@ 512 ) . dis mean dat a first magnitude star ( + 1 @.@ 00 ) is abt 2 @.@ 5 times brighter den a second magnitude ( + 2 @.@ 00 ) star , and about 100 times brighter than a sixth magnitude star ( + 6 @.@ 00 ) . Tdafaintest stars visible to thdaaked eye under gud seein conditions r about magnitude + 6 .

On both apparent and absolute magnitude scales , the smaller the magnitude number , the brighter the star ; the larger the magnitude number , the fainter the star . The brightest stars , on either scale , have negative magnitude numbers . The variation in brightness ( ΔL ) between two stars is calculated by subtracting the magnitude number of the brighter star ( mb ) from the magnitude number of the fainter star ( mf ) , then using the difference as an exponent for the base number 2 @.@ 512 ; that is to say :

On both apparent and absolute magnitude scales , the smaller the magnitude number , the brighter the star ; the larger the magnitude number , the fainter the star . The brightest stars , on either scale , <a href='got' title='1'><mark>have</mark></a> negative magnitude numbers . The variation in brightness ( ΔL ) between two stars is calculated by subtracting the magnitude number of the brighter star ( mb ) from the magnitude number of the fainter star ( mf ) , then using the difference as an exponent for the base number 2 @.@ 512 ; that is to say :

On both apparent and absolute magnitude scales , the smaller da magnitude number , tdabrighter the star ; thdaarger the magnitude number , the fainter the star . Thedaightest stars , on either scale , got negative magnitude numbers . The variation in brightness ( ΔL ) between two stars is calculated by subtracting the magnitude number of the daghter star ( mb ) from the magnitude number of the fdater star ( mf ) , then usin the difference as an exponent fir the badanumber 2 @.@ 512 ; that is to say :

<formula>

<formula>

<formula>

<formula>

<formula>

<formula>

Relative to both luminosity and distance from Earth , a star 's absolute magnitude ( M ) and apparent magnitude ( m ) are not equivalent ; for example , the bright star Sirius has an apparent magnitude of − 1 @.@ 44 , but it has an absolute magnitude of + 1 @.@ 41 .

Relative to both luminosity and distance from Earth , a star <a href='null_genetive' title='1'><mark>'s</mark></a>absolute magnitude ( M ) and apparent magnitude ( m ) <a href='negative_concord' title='2'><mark>are</mark></a> <a href='negative_concord' title='3'><mark>not</mark></a>equivalent ; for example , the bright star Sirius <a href='got' title='4'><mark>has</mark></a> an apparent magnitude of − 1 @.@ 44 , but it <a href='got' title='5'><mark>has</mark></a> an absolute magnitude of + 1 @.@ 41 .

Relative to both luminosity and distance from Earth , a star absolute magnitude ( M ) and apparent magnitude ( m ) ain't equivalent ; fa example , the bright star Sirius got an apparent magnitude of − 1 @.@ 44 , but it got an absolute magnitude of + 1 @.@ 41 .

The Sun has an apparent magnitude of − 26 @.@ 7 , but its absolute magnitude is only + 4 @.@ 83 . Sirius , the brightest star in the night sky as seen from Earth , is approximately 23 times more luminous than the Sun , while Canopus , the second brightest star in the night sky with an absolute magnitude of − 5 @.@ 53 , is approximately 14 @,@ 000 times more luminous than the Sun . Despite Canopus being vastly more luminous than Sirius , however , Sirius appears brighter than Canopus . This is because Sirius is merely 8 @.@ 6 light @-@ years from the Earth , while Canopus is much farther away at a distance of 310 light @-@ years .

The Sun <a href='got' title='1'><mark>has</mark></a> an apparent magnitude of − 26 @.@ 7 , but its absolute magnitude <a href='drop_aux' title='2'><mark>is</mark></a>only + 4 @.@ 83 . Sirius , the brightest star in the night sky as seen from Earth , <a href='drop_aux' title='3'><mark>is</mark></a>approximately 23 times more luminous than the Sun , while Canopus , the second brightest star in the night sky with an absolute magnitude of − 5 @.@ 53 , <a href='drop_aux' title='4'><mark>is</mark></a>approximately 14 @,@ 000 times more luminous than the Sun . Despite Canopus being vastly more luminous than Sirius , however , Sirius <a href='uninflect' title='5'><mark>appears</mark></a> brighter than Canopus . This is because Sirius <a href='drop_aux' title='6'><mark>is</mark></a>merely 8 @.@ 6 light @-@ years from the Earth , while Canopus <a href='drop_aux' title='7'><mark>is</mark></a>much farther away at a distance of 310 light @-@ years .

The Sun got an apparent magnitude of − 26 @.@ 7 , but its absolute magnitude only + 4 @.@ 83 . Sirius , the brightest star in the nite sky as seen from Earth , approximately 23 times more luminous than the Sun , while Canopus , the second brightest star in da night sky with an absolute magnitude of − 5 @.@ 53 , approximately 14 @,@ 000 times more luminous than the Sun . Despite Canopus being vastly more luminous than Sirius , however , Sirius appear brighter den Canopus . This is because Sirius merely 8 @.@ 6 light @-@ years from tdaEarth , while Canopus much farther away at a distance of 310 light @-@ yrs .

As of 2006 , the star with the highest known absolute magnitude is LBV 1806 @-@ 20 , with a magnitude of − 14 @.@ 2 . This star is at least 5 @,@ 000 @,@ 000 times more luminous than the Sun . The least luminous stars that are currently known are located in the NGC 6397 cluster . The faintest red dwarfs in the cluster were magnitude 26 , while a 28th magnitude white dwarf was also discovered . These faint stars are so dim that their light is as bright as a birthday candle on the Moon when viewed from the Earth .

As of 2006 , the star with the highest known absolute magnitude <a href='drop_aux' title='1'><mark>is</mark></a>LBV 1806 @-@ 20 , with a magnitude of − 14 @.@ 2 . This star <a href='drop_aux' title='2'><mark>is</mark></a>at least 5 @,@ 000 @,@ 000 times more luminous than the Sun . The least luminous stars <a href='null_relcl' title='3'><mark>that</mark></a>are currently known are located in the NGC 6397 cluster . The faintest red dwarfs in the cluster <a href='uninflect' title='4'><mark>were</mark></a> magnitude 26 , while a 28th magnitude white dwarf was also discovered . These faint stars <a href='drop_aux' title='5'><mark>are</mark></a>so dim that their light is as bright as a birthday candle on the Moon when viewed from the Earth .

As of 2006 , the star wit the highest known absolute magnitude LBV 1806 @-@ 20 , with a magnitude of − 14 @.@ 2 . This star at least 5 @,@ 000 @,@ 000 times more luminous than da Sun . The least luminous stars r currently known are located in tdaNGC 6397 cluster . Thdaaintest red dwarfs in the cluster was magnitude 26 , while a 28th magnitude white dwarf was also discovered . These faint stars soo dim dat their light is as bright as a birthday candle on the Moon when viewed from the Earth .

= = Classification = =

= = Classification = =

= = Classification = =

The current stellar classification system originated in the early 20th century , when stars were classified from A to Q based on the strength of the hydrogen line . It thought that the hydrogen line strength was a simple linear function of temperature . Rather , it was more complicated ; it strengthened with increasing temperature , it peaked near 9000 K , and then declined at greater temperatures . When the classifications were reordered by temperature , it more closely resembled the modern scheme .

The current stellar classification system originated in the early 20th century , when stars <a href='uninflect' title='1'><mark>were</mark></a> classified from A to Q based on the strength of the hydrogen line . It thought that the hydrogen line strength was a simple linear function of temperature . Rather , it was more complicated ; it strengthened with increasing temperature , it peaked near 9000 K , and then declined at greater temperatures . When the classifications <a href='uninflect' title='2'><mark>were</mark></a> reordered by temperature , it more closely resembled the modern scheme .

Da current stellar classification system originated in the early 20th century , when stars was classified from A to Q based on tdastrength of thdaydrogen line . It thought that thedadrogen line strength was a simple linear function of temperature . Rather , it was more complicated ; it strengthened wit increasing temperature , it peaked near 9000 K , and then declined at greater temperatures . When the classifications was reordered by temperature , it more closely resembled the modern scheme .

Stars are given a single @-@ letter classification according to their spectra , ranging from type O , which are very hot , to M , which are so cool that molecules may form in their atmospheres . The main classifications in order of decreasing surface temperature are : O , B , A , F , G , K , and M. A variety of rare spectral types are given special classifications . The most common of these are types L and T , which classify the coldest low @-@ mass stars and brown dwarfs . Each letter has 10 sub @-@ divisions , numbered from 0 to 9 , in order of decreasing temperature . However , this system breaks down at extreme high temperatures as classes O0 and O1 may not exist .

Stars are given a single @-@ letter classification according to their spectra , ranging from type O , which <a href='drop_aux' title='1'><mark>are</mark></a>very hot , to M , which <a href='drop_aux' title='2'><mark>are</mark></a>so cool that molecules may form in their atmospheres . The main classifications in order of decreasing surface temperature are : O , B , A , F , G , K , and M. A variety of rare spectral types are given special classifications . The most common of these <a href='drop_aux' title='3'><mark>are</mark></a>types L and T , which classify the coldest low @-@ mass stars and brown dwarfs . Each letter <a href='got' title='4'><mark>has</mark></a> 10 sub @-@ divisions , numbered from 0 to 9 , in order of decreasing temperature . However , this system <a href='uninflect' title='5'><mark>breaks</mark></a> down at extreme high temperatures as classes O0 and O1 may not exist .

Stars are given a single @-@ letter classification according to their spectra , ranging from type O , which very hot , to M , which soo coo that molecules may form in their atmospheres . da main classifications in order of decreasing surface temperature r : O , B , A , F , G , K , and M. A variety of rare spectral types arriven special classifications . Tdamost common of dem types L and T , which classify the coldest low @-@ mass stars and brown dwarfs . Each letter got 10 sub @-@ divisions , numbered from 0 to 9 , in order of decreasing temperature . However , this system break down at extreme high temperatures as classes O0 and O1 may not exist .

In addition , stars may be classified by the luminosity effects found in their spectral lines , which correspond to their spatial size and is determined by their surface gravity . These range from 0 ( hypergiants ) through III ( giants ) to V ( main sequence dwarfs ) ; some authors add VII ( white dwarfs ) . Most stars belong to the main sequence , which consists of ordinary hydrogen @-@ burning stars . These fall along a narrow , diagonal band when graphed according to their absolute magnitude and spectral type . The Sun is a main sequence G2V yellow dwarf of intermediate temperature and ordinary size .

In addition , stars may be classified by the luminosity effects found in their spectral lines , which correspond to their spatial size and is determined by their surface gravity . These range from 0 ( hypergiants ) through III ( giants ) to V ( main sequence dwarfs ) ; some authors add VII ( white dwarfs ) . Most stars belong to the main sequence , which <a href='uninflect' title='1'><mark>consists</mark></a> of ordinary hydrogen @-@ burning stars . These fall along a narrow , diagonal band when graphed according to their absolute magnitude and spectral type . The Sun <a href='drop_aux' title='2'><mark>is</mark></a>a main sequence G2V yellow dwarf of intermediate temperature and ordinary size .

In addition , stars may be classified by the luminosity effects found in their spectral lines , which correspond to their spatial size and is determined by their surface gravity . These range from 0 ( hypergiants ) through III ( giants ) to V ( main sequence dwarfs ) ; sum authors add VII ( white dwarfs ) . Most stars belong to the main sequence , which consist of ordinary hydrogen @-@ burning stars . dese fall along a narrow , diagonal band when graphed according to their absolute magnitude and spectral type . The Sun a main sequence G2V yellow dwarf of intermediate temperature and ordinary size .

Additional nomenclature , in the form of lower @-@ case letters added to the end of the spectral type to indicate peculiar features of the spectrum . For example , an " e " can indicate the presence of emission lines ; " m " represents unusually strong levels of metals , and " var " can mean variations in the spectral type .

Additional nomenclature , in the form of lower @-@ case letters added to the end of the spectral type to indicate peculiar features of the spectrum . For example , an " e " can indicate the presence of emission lines ; " m " <a href='uninflect' title='1'><mark>represents</mark></a> unusually strong levels of metals , and " var " can mean variations in the spectral type .

Additional nomenclature , in the form of lower @-@ case letters added to the end of da spectral type to indicate peculiar features of tdaspectrum . For example , an " e " can indicate thdaresence of emission lines ; " m " represent unusually strong levels of metals , and " var " can mean variations in the spectral type .

White dwarf stars have their own class that begins with the letter D. This is further sub @-@ divided into the classes DA , DB , DC , DO , DZ , and DQ , depending on the types of prominent lines found in the spectrum . This is followed by a numerical value that indicates the temperature .

White dwarf stars <a href='got' title='1'><mark>have</mark></a> their own class <a href='null_relcl' title='2'><mark>that</mark></a><a href='uninflect' title='3'><mark>begins</mark></a> with the letter D. This <a href='drop_aux' title='4'><mark>is</mark></a>further sub @-@ divided into the classes DA , DB , DC , DO , DZ , and DQ , depending on the types of prominent lines found in the spectrum . This is followed by a numerical value <a href='null_relcl' title='5'><mark>that</mark></a><a href='uninflect' title='6'><mark>indicates</mark></a> the temperature .

White dwarf stars got their own class begin with da letter D. dis further sub @-@ divided into tdaclasses DA , DB , DC , DO , DZ , and DQ , depending on the types of prominent lines found in the spectrum . Tdisis followed by a numerical value indicate the temperature .

= = Variable stars = =

= = Variable stars = =

= = Variable stars = =

Variable stars have periodic or random changes in luminosity because of intrinsic or extrinsic properties . Of the intrinsically variable stars , the primary types can be subdivided into three principal groups .

Variable stars <a href='got' title='1'><mark>have</mark></a> periodic or random changes in luminosity because of intrinsic or extrinsic properties . Of the intrinsically variable stars , the primary types can be subdivided into three principal groups .

Variable stars got periodic or random changes in luminosity because of intrinsic or extrinsic properties . Of the intrinsically variable stars , da primary types can b subdivided into three principal groups .

During their stellar evolution , some stars pass through phases where they can become pulsating variables . Pulsating variable stars vary in radius and luminosity over time , expanding and contracting with periods ranging from minutes to years , depending on the size of the star . This category includes Cepheid and Cepheid @-@ like stars , and long @-@ period variables such as Mira .

During their stellar evolution , some stars pass through phases where they can become pulsating variables . Pulsating variable stars vary in radius and luminosity over time , expanding and contracting with periods ranging from minutes to years , depending on the size of the star . This category <a href='uninflect' title='1'><mark>includes</mark></a> Cepheid and Cepheid @-@ like stars , and long @-@ period variables such as Mira .

During their stellar evolution , sum stars pass thru phases where they can become pulsating variables . Pulsating variable stars vary in radius and luminosity over time , expanding and contracting with periods ranging from minutes to yrs , depending on da size of the star . This category include Cepheid and Cepheid @-@ like stars , and long @-@ period variables such as Mira .

Eruptive variables are stars that experience sudden increases in luminosity because of flares or mass ejection events . This group includes protostars , Wolf @-@ Rayet stars , and flare stars , as well as giant and supergiant stars .

Eruptive variables <a href='drop_aux' title='1'><mark>are</mark></a>stars <a href='null_relcl' title='2'><mark>that</mark></a>experience sudden increases in luminosity because of flares or mass ejection events . This group <a href='uninflect' title='3'><mark>includes</mark></a> protostars , Wolf @-@ Rayet stars , and flare stars , as well as giant and supergiant stars .

Eruptive variables stars experience sudden increases in luminosity cus of flares or mass ejection events . This group include protostars , Wolf @-@ Rayet stars , and flare stars , as well as bigass and supergiant stars .

Cataclysmic or explosive variable stars are those that undergo a dramatic change in their properties . This group includes novae and supernovae . A binary star system that includes a nearby white dwarf can produce certain types of these spectacular stellar explosions , including the nova and a Type 1a supernova . The explosion is created when the white dwarf accretes hydrogen from the companion star , building up mass until the hydrogen undergoes fusion . Some novae are also recurrent , having periodic outbursts of moderate amplitude .

Cataclysmic or explosive variable stars <a href='drop_aux' title='1'><mark>are</mark></a>those <a href='null_relcl' title='2'><mark>that</mark></a>undergo a dramatic change in their properties . This group <a href='uninflect' title='3'><mark>includes</mark></a> novae and supernovae . A binary star system <a href='null_relcl' title='4'><mark>that</mark></a><a href='uninflect' title='5'><mark>includes</mark></a> a nearby white dwarf can produce certain types of these spectacular stellar explosions , including the nova and a Type 1a supernova . The explosion is created when the white dwarf accretes hydrogen from the companion star , building up mass until the hydrogen undergoes fusion . Some novae <a href='drop_aux' title='6'><mark>are</mark></a>also recurrent , having periodic outbursts of moderate amplitude .

Cataclysmic or explosive variable stars those undergo a petty change in their properties . dis group include novae and supernovae . A binary star system include a nearby white dwarf can produce certain types of dese spectacular stellar explosions , including the nova and a Type 1a supernova . The explosion is created when the white dwarf accretes hydrogen from the companion star , building up mass until the hydrogen undergoes fusion . Some novae also recurrent , having periodic outbursts of moderate amplitude .

Stars can also vary in luminosity because of extrinsic factors , such as eclipsing binaries , as well as rotating stars that produce extreme starspots . A notable example of an eclipsing binary is Algol , which regularly varies in magnitude from 2 @.@ 3 to 3 @.@ 5 over a period of 2 @.@ 87 days .

Stars can also vary in luminosity because of extrinsic factors , such as eclipsing binaries , as well as rotating stars <a href='null_relcl' title='1'><mark>that</mark></a>produce extreme starspots . A notable example of an eclipsing binary <a href='drop_aux' title='2'><mark>is</mark></a>Algol , which regularly <a href='uninflect' title='3'><mark>varies</mark></a> in magnitude from 2 @.@ 3 to 3 @.@ 5 over a period of 2 @.@ 87 days .

Stars can also vary in luminosity because of extrinsic factors , such as eclipsing binaries , as well as rotating stars produce extreme starspots . A notable example of an eclipsing binary Algol , which regularly vary in magnitude from 2 @.@ 3 to 3 @.@ 5 over a period of 2 @.@ 87 days .

= = Structure = =

= = Structure = =

= = Structure = =

The interior of a stable star is in a state of hydrostatic equilibrium : the forces on any small volume almost exactly counterbalance each other . The balanced forces are inward gravitational force and an outward force due to the pressure gradient within the star . The pressure gradient is established by the temperature gradient of the plasma ; the outer part of the star is cooler than the core . The temperature at the core of a main sequence or giant star is at least on the order of 107 K. The resulting temperature and pressure at the hydrogen @-@ burning core of a main sequence star are sufficient for nuclear fusion to occur and for sufficient energy to be produced to prevent further collapse of the star .

The interior of a stable star is in a state of hydrostatic equilibrium : the forces on any small volume almost exactly counterbalance each other . The balanced forces <a href='drop_aux' title='1'><mark>are</mark></a>inward gravitational force and an outward force due to the pressure gradient within the star . The pressure gradient is established by the temperature gradient of the plasma ; the outer part of the star is cooler than the core . The temperature at the core of a main sequence or giant star is at least on the order of 107 K. The resulting temperature and pressure at the hydrogen @-@ burning core of a main sequence star <a href='drop_aux' title='2'><mark>are</mark></a>sufficient for nuclear fusion to occur and for sufficient energy to be produced to prevent further collapse of the star .

Da interior of a stable star is in a state of hydrostatic equilibrium : the forces on any small volume almost exactly counterbalance each other . The balanced forces inward gravitational force and an outward force due to the pressure gradient within the star . The pressure gradient is established by the temperature gradient of tdaplasma ; the outer part of the star is cooler than the core . Thdaemperature at thedare of a main sequence or bigass star is at least on the order of 107 K. The daulting temperature and pressure at the hdaogen @-@ burning core of a main sequence star sufficient for nuclear fusion to occur and fir sufficient energy to be produced to prevent further collapse of the star .

As atomic nuclei are fused in the core , they emit energy in the form of gamma rays . These photons interact with the surrounding plasma , adding to the thermal energy at the core . Stars on the main sequence convert hydrogen into helium , creating a slowly but steadily increasing proportion of helium in the core . Eventually the helium content becomes predominant , and energy production ceases at the core . Instead , for stars of more than 0 @.@ 4 M ☉ , fusion occurs in a slowly expanding shell around the degenerate helium core .

As atomic nuclei are fused in the core , they emit energy in the form of gamma rays . These photons interact with the surrounding plasma , adding to the thermal energy at the core . Stars on the main sequence convert hydrogen into helium , creating a slowly but steadily increasing proportion of helium in the core . Eventually the helium content <a href='uninflect' title='1'><mark>becomes</mark></a> predominant , and energy production ceases at the core . Instead , for stars of more than 0 @.@ 4 M ☉ , fusion <a href='uninflect' title='2'><mark>occurs</mark></a> in a slowly expanding shell around the degenerate helium core .

As atomic nuclei are fused in da core , they emit energy in tdaform of gamma rays . These photons interact with thdaurrounding plasma , adding to the thermal energy at the core . Stars on the main sequence convert hydrogen into helium , creating a slowly but steadily increasing proportion of helium in thedare . Eventually the daium content become predominant , and energy production ceases at the core . Instead , fir stars of more than 0 @.@ 4 M ☉ , fusion occur in a slowly expanding shell around the ddanerate helium core .

In addition to hydrostatic equilibrium , the interior of a stable star will also maintain an energy balance of thermal equilibrium . There is a radial temperature gradient throughout the interior that results in a flux of energy flowing toward the exterior . The outgoing flux of energy leaving any layer within the star will exactly match the incoming flux from below .

In addition to hydrostatic equilibrium , the interior of a stable star will also maintain an energy balance of thermal equilibrium . <a href='dey_it' title='1'><mark>There</mark></a> is a radial temperature gradient throughout the interior <a href='null_relcl' title='2'><mark>that</mark></a><a href='uninflect' title='3'><mark>results</mark></a> in a flux of energy flowing toward the exterior . The outgoing flux of energy leaving any layer within the star will exactly match the incoming flux from below .

In addition to hydrostatic equilibrium , the interior of a stable star gon also maintain an energy balance of thermal equilibrium . It is a radial temperature gradient throughout the interior result in a flux of energy flowing toward the exterior . The outgoing flux of energy leavin any layer within da star wgonexactly match the incoming flux from below .

The radiation zone is the region of the stellar interior where the flux of energy outward is dependent on radiative heat transfer , since convective heat transfer is inefficient in that zone . In this region the plasma will not be perturbed , and any mass motions will die out . If this is not the case , however , then the plasma becomes unstable and convection will occur , forming a convection zone . This can occur , for example , in regions where very high energy fluxes occur , such as near the core or in areas with high opacity ( making radiatative heat transfer inefficient ) as in the outer envelope .

The radiation zone <a href='drop_aux' title='1'><mark>is</mark></a>the region of the stellar interior where the flux of energy outward <a href='drop_aux' title='2'><mark>is</mark></a>dependent on radiative heat transfer , since convective heat transfer <a href='drop_aux' title='3'><mark>is</mark></a>inefficient in that zone . In <a href='None' title='4'><mark>this</mark></a><a href='negative_concord' title='5'><mark>region</mark></a> the plasma will not be perturbed , and any mass motions will die out . If this <a href='negative_concord' title='6'><mark>is</mark></a> <a href='negative_concord' title='7'><mark>not</mark></a><a href='None' title='8'><mark>the</mark></a><a href='negative_concord' title='9'><mark>case</mark></a> , however , then the plasma <a href='uninflect' title='10'><mark>becomes</mark></a> unstable and convection will occur , forming a convection zone . This can occur , for example , in regions where very high energy fluxes occur , such as near the core or in areas with high opacity ( making radiatative heat transfer inefficient ) as in the outer envelope .

The radiation zone da region of the stellar interior where the flux of energy outward dependent on radiative heat transfer , since convective heat transfer inefficient in that zone . In no region tdaplasma gon not b perturbed , and any mass motions wgondie out . If dis ain't no case , however , then the plasma become unstable and convection will occur , forming a convection zone . Tdiscan occur , for example , in regions where very high energy fluxes occur , such as near the core or in areas with high opacity ( making radiatative heat transfer inefficient ) as in the outer envelope .

The occurrence of convection in the outer envelope of a main sequence star depends on the star 's mass . Stars with several times the mass of the Sun have a convection zone deep within the interior and a radiative zone in the outer layers . Smaller stars such as the Sun are just the opposite , with the convective zone located in the outer layers . Red dwarf stars with less than 0 @.@ 4 M ☉ are convective throughout , which prevents the accumulation of a helium core . For most stars the convective zones will also vary over time as the star ages and the constitution of the interior is modified .

The occurrence of convection in the outer envelope of a main sequence star <a href='uninflect' title='1'><mark>depends</mark></a> on the star <a href='null_genetive' title='2'><mark>'s</mark></a>mass . Stars with several times the mass of the Sun <a href='got' title='3'><mark>have</mark></a> a convection zone deep within the interior and a radiative zone in the outer layers . Smaller stars such as the Sun <a href='drop_aux' title='4'><mark>are</mark></a>just the opposite , with the convective zone located in the outer layers . Red dwarf <a href='uninflect' title='5'><mark>stars</mark></a> with less than 0 @.@ 4 M ☉ are convective throughout , which <a href='uninflect' title='6'><mark>prevents</mark></a> the accumulation of a helium core . For most stars the convective zones will also vary over time as the star ages and the constitution of the interior is modified .

Da occurrence of convection in the outer envelope of a main sequence star depend on tdastar mass . Stars with several times thdaass of thedan got a convection zone deep within the interior and a radiative zone in the outer layers . Smaller stars such as the Sun jus the opposite , with the convective zone located in the outer layers . Red dwarf star with less than 0 @.@ 4 M ☉ are convective throughout , which prevent the daumulation of a helium core . For most stars the convective zones will also vary over time as the star ages and the constitution of the interior is modified .

The photosphere is that portion of a star that is visible to an observer . This is the layer at which the plasma of the star becomes transparent to photons of light . From here , the energy generated at the core becomes free to propagate into space . It is within the photosphere that sun spots , regions of lower than average temperature , appear .

The photosphere <a href='drop_aux' title='1'><mark>is</mark></a>that portion of a star <a href='null_relcl' title='2'><mark>that</mark></a><a href='drop_aux' title='3'><mark>is</mark></a>visible to an observer . This <a href='drop_aux' title='4'><mark>is</mark></a>the layer at which the plasma of the star <a href='uninflect' title='5'><mark>becomes</mark></a> transparent to photons of light . From here , the energy generated at the core <a href='uninflect' title='6'><mark>becomes</mark></a> free to propagate into space . It is within the photosphere <a href='null_relcl' title='7'><mark>that</mark></a>sun <a href='uninflect' title='8'><mark>spots</mark></a> , regions of lower than average temperature , appear .

The photosphere that portion of a star visible to an observer . This the layer at which da plasma of tdastar become transparent to photons of light . From here , the energy generated at thdaore become free to propagate into space . It is within thedaotosphere sun spot , regions of lower den average temperature , appear .

Above the level of the photosphere is the stellar atmosphere . In a main sequence star such as the Sun , the lowest level of the atmosphere , just above the photosphere , is the thin chromosphere region , where spicules appear and stellar flares begin . Above this is the transition region , where the temperature rapidly increases within a distance of only 100 km ( 62 mi ) . Beyond this is the corona , a volume of super @-@ heated plasma that can extend outward to several million kilometres . The existence of a corona appears to be dependent on a convective zone in the outer layers of the star . Despite its high temperature , and the corona emits very little light , due to its low gas density . The corona region of the Sun is normally only visible during a solar eclipse .

Above the level of the photosphere <a href='drop_aux' title='1'><mark>is</mark></a>the stellar atmosphere . In a main sequence star such as the Sun , the lowest level of the atmosphere , just above the photosphere , <a href='drop_aux' title='2'><mark>is</mark></a>the thin chromosphere region , where spicules appear and stellar flares begin . Above this is the transition region , where the temperature rapidly <a href='uninflect' title='3'><mark>increases</mark></a> within a distance of only 100 km ( 62 mi ) . Beyond this <a href='drop_aux' title='4'><mark>is</mark></a>the corona , a volume of super @-@ heated plasma <a href='null_relcl' title='5'><mark>that</mark></a>can extend outward to several million kilometres . The existence of a corona <a href='uninflect' title='6'><mark>appears</mark></a> to be dependent on a convective zone in the outer layers of the star . Despite its high temperature , and the corona <a href='uninflect' title='7'><mark>emits</mark></a> very little light , due to its low gas density . The corona region of the Sun <a href='drop_aux' title='8'><mark>is</mark></a>normally only visible during a solar eclipse .

Above the level of the photosphere the stellar atmosphere . In a main sequence star such as da Sun , the lowest level of the atmosphere , just above tdaphotosphere , the thin chromosphere region , where spicules appear and stellar flares begin . Above dis is the transition region , where the temperature rapidly increase within a distance of only 100 km ( 62 mi ) . Beyond tdisthe corona , a volume of super @-@ heated plasma can extend outward to several million kilometres . The existence of a corona appear to be dependent on a convective zone in the outer layers of thdatar . Despite its high temperature , and the corona emit very lil light , due to its low gas density . The corona region of the Sun normally only visible during a solar eclipse .

From the corona , a stellar wind of plasma particles expands outward from the star , until it interacts with the interstellar medium . For the Sun , the influence of its solar wind extends throughout a bubble @-@ shaped region called the heliosphere .

From the corona , a stellar wind of plasma particles <a href='uninflect' title='1'><mark>expands</mark></a> outward from the star , until it <a href='uninflect' title='2'><mark>interacts</mark></a> with the interstellar medium . For the Sun , the influence of its solar wind <a href='uninflect' title='3'><mark>extends</mark></a> throughout a bubble @-@ shaped region called the heliosphere .

From da corona , a stellar wind of plasma particles expand outward from tdastar , until it interact witt the interstellar medium . fir the Sun , thdanfluence of its solar wind extend throughout a bubble @-@ shaped region called the heliosphere .

= = Nuclear fusion reaction pathways = =

= = Nuclear fusion reaction pathways = =

= = Nuclear fusion reaction pathways = =

A variety of nuclear fusion reactions take place in the cores of stars , that depend upon their mass and composition . When nuclei fuse , the mass of the fused product is less than the mass of the original parts . This lost mass is converted to electromagnetic energy , according to the mass @-@ energy equivalence relationship E = mc2 .

A variety of nuclear fusion reactions take place in the cores of stars , that depend upon their mass and composition . When nuclei fuse , the mass of the fused product <a href='drop_aux' title='1'><mark>is</mark></a>less than the mass of the original parts . This lost mass is converted to electromagnetic energy , according to the mass @-@ energy equivalence relationship E = mc2 .

A variety of nuclear fusion reactions take place in the cores of stars , dat depend upon their mass and composition . When nuclei fuse , da mass of the fused product less than tdamass of thdariginal parts . This lost mass is converted to electromagnetic energy , according to the mass @-@ energy equivalence relationship E = mc2 .

The hydrogen fusion process is temperature @-@ sensitive , so a moderate increase in the core temperature will result in a significant increase in the fusion rate . As a result , the core temperature of main sequence stars only varies from 4 million kelvin for a small M @-@ class star to 40 million kelvin for a massive O @-@ class star .

The hydrogen fusion process <a href='drop_aux' title='1'><mark>is</mark></a>temperature @-@ sensitive , so a moderate increase in the core temperature will result in a significant increase in the fusion rate . As a result , the core temperature of main sequence stars only <a href='uninflect' title='2'><mark>varies</mark></a> from 4 million kelvin for a small M @-@ class star to 40 million kelvin for a massive O @-@ class star .

The hydrogen fusion process temperature @-@ sensitive , soo a moderate increase in the core temperature will result in a significant increase in da fusion rate . As a result , the core temperature of main sequence stars only vary from 4 million kelvin fa a small M @-@ class star to 40 million kelvin for a massive O @-@ class star .

In the Sun , with a 10 @-@ million @-@ kelvin core , hydrogen fuses to form helium in the proton @-@ proton chain reaction :

In the Sun , with a 10 @-@ million @-@ kelvin core , hydrogen fuses to form helium in the proton @-@ proton chain reaction :

In the Sun , with a 10 @-@ million @-@ kelvin core , hydrogen fuses to form helium in the proton @-@ proton chain reaction :

41H → 22H + 2e + + 2νe ( 2 x 0 @.@ 4 MeV )

41H → 22H + 2e + + 2νe ( 2 x 0 @.@ 4 MeV )

41H → 22H + 2e + + 2νe ( 2 x 0 @.@ 4 MeV )

2e + + 2e- → 2γ ( 2 x 1 @.@ 0 MeV )

2e + + 2e- → 2γ ( 2 x 1 @.@ 0 MeV )

2e + + 2e- → 2γ ( 2 x 1 @.@ 0 MeV )

21H + 22H → 23He + 2γ ( 2 x 5 @.@ 5 MeV )

21H + 22H → 23He + 2γ ( 2 x 5 @.@ 5 MeV )

21H + 22H → 23He + 2γ ( 2 x 5 @.@ 5 MeV )

23He → 4He + 21H ( 12 @.@ 9 MeV )

23He → 4He + 21H ( 12 @.@ 9 MeV )

23He → 4He + 21H ( 12 @.@ 9 MeV )

These reactions result in the overall reaction :

These reactions result in the overall reaction :

These reactions result in da overall reaction :

41H → 4He + 2e + + 2γ + 2νe ( 26 @.@ 7 MeV )

41H → 4He + 2e + + 2γ + 2νe ( 26 @.@ 7 MeV )

41H → 4He + 2e + + 2γ + 2νe ( 26 @.@ 7 MeV )

where e + is a positron , γ is a gamma ray photon , νe is a neutrino , and H and He are isotopes of hydrogen and helium , respectively . The energy released by this reaction is in millions of electron volts , which is actually only a tiny amount of energy . However enormous numbers of these reactions occur constantly , producing all the energy necessary to sustain the star 's radiation output . In comparison , the combustion of two hydrogen gas molecules with one oxygen gas molecule releases only 5 @.@ 7 eV .

where e + <a href='drop_aux' title='1'><mark>is</mark></a>a positron , γ is a gamma ray photon , <a href='uninflect' title='2'><mark>νe</mark></a> is a neutrino , and H and He <a href='drop_aux' title='3'><mark>are</mark></a>isotopes of hydrogen and helium , respectively . The energy released by this reaction is in millions of electron volts , which <a href='drop_aux' title='4'><mark>is</mark></a>actually only a tiny amount of energy . However enormous numbers of these reactions occur constantly , producing all the energy necessary to sustain the star <a href='null_genetive' title='5'><mark>'s</mark></a>radiation output . In comparison , the combustion of two hydrogen gas molecules with one oxygen gas molecule <a href='uninflect' title='6'><mark>releases</mark></a> only 5 @.@ 7 eV .

Where e + a positron , γ is a gamma ray photon , νed is a neutrino , and H and He isotopes of hydrogen and helium , respectively . da energy released by this reaction is in millions of electron volts , which actually only a tiny amount of energy . However enormous numbers of dem reactions occur constantly , producing alll the energy necessary to sustain the star radiation output . In comparison , tdacombustion of two hydrogen gas molecules with one oxygen gas molecule release only 5 @.@ 7 eV .

In more massive stars , helium is produced in a cycle of reactions catalyzed by carbon called the carbon @-@ nitrogen @-@ oxygen cycle .

In more massive stars , helium is produced in a cycle of reactions catalyzed by carbon called the carbon @-@ nitrogen @-@ oxygen cycle .

In more massive stars , helium is produced in a cycle of reactions catalyzed by carbon called da carbon @-@ nitrogen @-@ oxygen cycle .

In evolved stars with cores at 100 million kelvin and masses between 0 @.@ 5 and 10 M ☉ , helium can be transformed into carbon in the triple @-@ alpha process that uses the intermediate element beryllium :

In evolved stars with cores at 100 million kelvin and masses between 0 @.@ 5 and 10 M ☉ , helium can be transformed into carbon in the triple @-@ alpha process <a href='null_relcl' title='1'><mark>that</mark></a><a href='uninflect' title='2'><mark>uses</mark></a> the intermediate element beryllium :

In evolved stars with cores at 100 million kelvin and masses between 0 @.@ 5 and 10 M ☉ , helium can be transformed into carbon in da triple @-@ alpha process use tdaintermediate element beryllium :

4He + 4He + 92 keV → 8 * Be

4He + 4He + 92 keV → 8 * Be

4He + 4He + 92 keV → 8 * Be

4He + 8 * Be + 67 keV → 12 * C

4He + 8 * Be + 67 keV → 12 * C

4He + 8 * Be + 67 keV → 12 * C

12 * C → 12C + γ + 7 @.@ 4 MeV

12 * C → 12C + γ + 7 @.@ 4 MeV

12 * C → 12C + γ + 7 @.@ 4 MeV

For an overall reaction of :

For an overall reaction of :

Fa an overall reaction of :

34He → 12C + γ + 7 @.@ 2 MeV

34He → 12C + γ + 7 @.@ 2 MeV

34He → 12C + γ + 7 @.@ 2 MeV

In massive stars , heavier elements can also be burned in a contracting core through the neon burning process and oxygen burning process . The final stage in the stellar nucleosynthesis process is the silicon burning process that results in the production of the stable isotope iron @-@ 56 , an endothermic process that consumes energy , and so further energy can only be produced through gravitational collapse .

In massive stars , heavier elements can also be burned in a contracting core through the neon burning process and oxygen burning process . The final stage in the stellar nucleosynthesis process <a href='drop_aux' title='1'><mark>is</mark></a>the silicon burning process <a href='null_relcl' title='2'><mark>that</mark></a><a href='uninflect' title='3'><mark>results</mark></a> in the production of the stable isotope iron @-@ 56 , an endothermic process <a href='null_relcl' title='4'><mark>that</mark></a><a href='uninflect' title='5'><mark>consumes</mark></a> energy , and so further energy can only be produced through gravitational collapse .

In massive stars , heavier elements can also be burned in a contracting core through da neon burning process and oxygen burning process . The final stage in the stellar nucleosynthesis process the silicon burnin process result in the production of the stable isotope iron @-@ 56 , an endothermic process consume energy , and soo further energy can only b produced thru gravitational collapse .

The example below shows the amount of time required for a star of 20 M ☉ to consume all of its nuclear fuel . As an O @-@ class main sequence star , it would be 8 times the solar radius and 62 @,@ 000 times the Sun 's luminosity .

The example below <a href='uninflect' title='1'><mark>shows</mark></a> the amount of time required for a star of 20 M ☉ to consume all of its nuclear fuel . As an O @-@ class main sequence star , it would be 8 times the solar radius and 62 @,@ 000 times the Sun <a href='null_genetive' title='2'><mark>'s</mark></a>luminosity .

The example below show da amount of time required for a star of 20 M ☉ to consume all of its nuclear fuel . As an O @-@ class main sequence star , it would be 8 times tdasolar radius and 62 @,@ 000 times the Sun luminosity .

= Perry the Platypus =

= Perry the Platypus =

= Perry the Platypus =

Perry the Platypus , also known as Agent P or simply Perry , is an anthropomorphic platypus from the animated series Phineas and Ferb . Perry was created by the series ' co @-@ founders , Dan Povenmire and Jeff " Swampy " Marsh . He first appeared along with the majority of the main cast in the pilot episode " Rollercoaster . " Perry is featured as the star of the B @-@ plot for every episode of the series , alongside his nemesis Dr. Heinz Doofenshmirtz . A mostly silent character , his lone vocal characteristic ( a rattling of Perry 's beak ) was provided by Dee Bradley Baker .

Perry the Platypus , also known as Agent P or simply Perry , <a href='drop_aux' title='1'><mark>is</mark></a>an anthropomorphic platypus from the animated series Phineas and Ferb . Perry was created by the series <a href='null_genetive' title='2'><mark>'</mark></a><a href='uninflect' title='3'><mark>co</mark></a> @-@ founders , Dan Povenmire and Jeff " Swampy " Marsh . He first appeared along with the majority of the main cast in the pilot episode " Rollercoaster . " Perry is featured as the star of the B @-@ plot for every episode of the series , alongside his nemesis Dr. Heinz Doofenshmirtz . A mostly silent character , his lone vocal characteristic ( a rattling of Perry <a href='null_genetive' title='4'><mark>'s</mark></a>beak ) was provided by Dee Bradley Baker .

Perry the Platypus , also known as Agent P or simply Perry , an anthropomorphic platypus from the animated series Phineas and Ferb . Perry was created by the series coed @-@ founders , Dan Povenmire and Jeff " Swampy " Marsh . He first appeared along witt da majority of the main cast in tdapilot episode " Rollercoaster . " Perry is featured as thdatar of the B @-@ plot for every episode of the series , alongside his nemesis Dr. Heinz Doofenshmirtz . A mostly silent character , his lone vocal characteristic ( a rattling of Perry beak ) was provided by Dee Bradley Baker .

Perry is the pet platypus of the Flynn @-@ Fletcher family , and is perceived as mindless and domesticated . In secret , however , he lives a double life as a member of an all @-@ animal espionage organization referred to as O.W.C.A. ( The Organization Without a Cool Acronym ) . Many secret entrances to his underground lair exist all around the house ; such as the side of the house , most notably the tree that his owners sit under in the backyard , and several other everyday objects that seem to elude the family 's attention . He engages in daily battles with Dr. Heinz Doofenshmirtz , an evil scientist who desires to take over the Tri @-@ state area with obscure contraptions that work perfectly according to his intended function but fail in his application of them every time .

Perry <a href='drop_aux' title='1'><mark>is</mark></a>the pet platypus of the Flynn @-@ Fletcher family , and is perceived as mindless and domesticated . In secret , however , he <a href='uninflect' title='2'><mark>lives</mark></a> a double life as a member of an all @-@ animal espionage organization referred to as O.W.C.A. ( The Organization Without a Cool Acronym ) . Many secret entrances to his underground lair exist all around the house ; such as the side of the house , most notably the tree that his owners sit under in the backyard , and several other everyday objects <a href='null_relcl' title='3'><mark>that</mark></a>seem to elude the family <a href='null_genetive' title='4'><mark>'s</mark></a>attention . He <a href='uninflect' title='5'><mark>engages</mark></a> in daily battles with Dr. Heinz Doofenshmirtz , an evil scientist <a href='null_relcl' title='6'><mark>who</mark></a><a href='uninflect' title='7'><mark>desires</mark></a> to take over the Tri @-@ state area with obscure contraptions <a href='null_relcl' title='8'><mark>that</mark></a>work perfectly according to his intended function but fail in his application of them every time .

Perry the pet platypus of the Flynn @-@ Fletcher fam , and is perceived as mindless and domesticated . In secret , however , he live a double life as a member of an all @-@ animal espionage organization referred to as O.wit.C.A. ( The Organization Without a coo Acronym ) . Many secret entrances to his underground lair exist all around the house ; such as the side of da house , most notably tdatree that his owners sit under in thdaackyard , and several other everyday objects seem to elude thedamily attention . He engage in daily battles with Dr. Heinz Doofenshmirtz , an evil scientist desire to take over the Tri @-@ state area with obscure contraptions work perfectly according to his intended function but fail in his application of em every time .

Perry was made a platypus because of the animal 's striking appearance and the lack of public knowledge of the animal , which allowed the writers to make things up about the species . Critical reception for the character from both professionals and fans have been considerably positive . Merchandising of the character include plush toys , t @-@ shirts , wooden toys , glasses , and coloring books , along with appearances in literature and a 2009 video game for the Nintendo DS .

Perry was made a platypus because of the animal <a href='null_genetive' title='1'><mark>'s</mark></a>striking appearance and the lack of public knowledge of the animal , which allowed the writers to make things up about the species . Critical reception for the character from both professionals and fans have been considerably positive . Merchandising of the character include plush toys , t @-@ shirts , wooden toys , glasses , and coloring books , along with appearances in literature and a 2009 video game for the Nintendo DS .

Perry was made a platypus becuz of da animal striking appearance and tdalack of public knowledge of the animal , which allowed thdariters to make things up bout the species . Critical reception fir thedaaracter from both professionals and fans have been considerably positive . Merchandising of the character include plush toys , t @-@ shirts , wooden toys , glasses , and coloring books , along with appearances in literature and a 2009 video game for the Nintendo DS .

= = Role in Phineas and Ferb = =

= = Role in Phineas and Ferb = =

= = Role in Phineas and Ferb = =

Perry is the docile pet platypus of the blended Flynn @-@ Fletcher family , who adopted him because his unfocused gaze made it seem as if he were looking at both Phineas and Ferb at the same time , as shown in the 2011 movie , Phineas and Ferb the Movie : Across the 2nd Dimension . Unbeknownst to them , Perry lives a double life as a crime @-@ fighting spy working for the " Organization Without a Cool Acronym " / The OWCA , going by the codename " Agent P. " He reports to his superior , Major Monogram , via telecast in his large , high @-@ tech , underground hideout . Every day , he engages in battles with the evil scientist Dr. Heinz Doofenshmirtz , who tries using inventions to take over the tri @-@ state area . Perry is always able to foil Doofenshmirtz 's plans and in doing so accidentally leads to the destruction of whatever form of contraption his owners , Phineas Flynn and Ferb Fletcher , are building in order to make summer better . Phineas and Ferb are aware that something happens to get rid of their scheme for the day , but do not know that Perry is the cause behind it and are largely dismissive of it . Their sister , Candace , also does not know that Perry is behind the destruction and is driven to near insanity trying to figure it out . Throughout the series , Perry is aware of Phineas and Ferb 's inventions , but is largely uninterested in them , save whenever he notices that their latest invention may help him thwart Doofenshmirtz .

Perry <a href='drop_aux' title='1'><mark>is</mark></a>the docile pet platypus of the blended Flynn @-@ Fletcher family , <a href='null_relcl' title='2'><mark>who</mark></a>adopted him because his unfocused gaze made it seem as if he <a href='uninflect' title='3'><mark>were</mark></a> looking at both Phineas and Ferb at the same time , as shown in the 2011 movie , Phineas and Ferb the Movie : Across the 2nd Dimension . Unbeknownst to them , Perry <a href='uninflect' title='4'><mark>lives</mark></a> a double life as a crime @-@ fighting spy working for the " Organization Without a Cool Acronym " / The OWCA , going by the codename " Agent P. " He <a href='uninflect' title='5'><mark>reports</mark></a> to his superior , Major Monogram , via telecast in his large , high @-@ tech , underground hideout . Every day , he <a href='uninflect' title='6'><mark>engages</mark></a> in battles with the evil scientist Dr. Heinz Doofenshmirtz , <a href='null_relcl' title='7'><mark>who</mark></a><a href='uninflect' title='8'><mark>tries</mark></a> using inventions to take over the tri @-@ state area . Perry <a href='drop_aux' title='9'><mark>is</mark></a>always able to foil Doofenshmirtz <a href='null_genetive' title='10'><mark>'s</mark></a>plans and in doing so accidentally <a href='uninflect' title='11'><mark>leads</mark></a> to the destruction of whatever form of contraption his owners , Phineas Flynn and Ferb Fletcher , are building in order to make summer better . Phineas and Ferb <a href='drop_aux' title='12'><mark>are</mark></a>aware that something <a href='uninflect' title='13'><mark>happens</mark></a> to get rid of their scheme for the day , but do not know that Perry is the cause behind it and <a href='drop_aux' title='14'><mark>are</mark></a>largely dismissive of it . Their sister , Candace , also <a href='uninflect' title='15'><mark>does</mark></a> not know that Perry is behind the destruction and is driven to near insanity trying to figure it out . Throughout the series , Perry <a href='drop_aux' title='16'><mark>is</mark></a>aware of Phineas and Ferb <a href='null_genetive' title='17'><mark>'s</mark></a>inventions , but <a href='drop_aux' title='18'><mark>is</mark></a>largely uninterested in them , save whenever he <a href='uninflect' title='19'><mark>notices</mark></a> that their latest invention may help him thwart Doofenshmirtz .

Perry the docile pet platypus of the blended Flynn @-@ Fletcher fam , adopted em because his unfocused gaze made it seem as if he was lookin at both Phineas and Ferb at the same time , as shown in the 2011 movie , Phineas and Ferb da Movie : Across tda2nd Dimension . Unbeknownst to them , Perry live a double life as a crime @-@ fighting spy workin for thda Organization w/o a Cool Acronym " / The OWCA , going by the codename " Agent P. " He report to his superior , Major Monogram , via telecast in his large , high @-@ tech , underground hideout . Every day , he engage in battles wit the evil scientist Dr. Heinz Doofenshmirtz , try using inventions to take over the tri @-@ state area . Perry always able to foil Doofenshmirtz plans and in doin soo accidentally lead to thedastruction of w.e form of contraption his owners , Phineas Flynn and Ferb Fletcher , r building in order to make summer betta . Phineas and Ferb aware dat something happen to get rid of their scheme for the da , but do not knoe tdatPerry is the cdae behind it and largely dismissive of it . Their sister , Candace , also do not know thdaterry is behind the destruction and is driven to near insanity tryna figure it outt . Throughout the series , Perry aware of Phineas and Ferb inventions , but largely uninterested in em , save whenever he notice that their latest invention may help hemthwart Doofenshmirtz .

Perry and Doofenshmirtz at first seem to loathe each other in the beginning of the series , and have been arch @-@ nemeses since the day they met . However , they are often cordial and friendly towards one another and it is said by Doofenshmirtz that Perry is his best friend , and Perry will often act to save Doofenshmirtz 's life when his plot inevitably blows up in his face . Habitually , their daily brawls involve Doofenshmirtz devising a scheme , which Perry goes to stop after being briefed by Major Monogram . He is trapped by Doofenshmirtz while trying to do so and is told of the doctor 's scheme , usually pertaining to some backstory or pet peeve . He then escapes and the two fight , Perry coming out victorious . The two rely on this daily structure , Doofenshmirtz even specifically mentioning it in " Journey to the Center of Candace " and in episodes such as " It 's About Time ! " in which Doofenshmirtz temporarily replaces Perry with secret agent Peter The Panda and they become depressed about not having each other to fight . Perry realizes he misses Doof too . When Perry does not arrive on the scene of Doofenshmirtz 's evil plan , the doctor hesitates to execute his plans and fears for where Perry has gone , though he notes that he " hopes something terrible has happened to him . " . Sometimes , they decided not to fight and have fun , as shown in " Happy New Year ! " and " Candace Disconnected " . On other occasions , depending on whatever situation Doofenshmirtz is facing , Perry would often help Doofenshmirtz with his non @-@ evil plans , such as helping him overcome evil scientist 's block , helping him put on a birthday party for his 16 @-@ year @-@ old daughter Vanessa , impressing a square dancing girl with programmable square dancing boots that Doofenshmritz created , working together to stop a raging platypus hunter from hunting them down , or helping him convince his rich ex @-@ wife to help pay off his mortgage debt . Also , Perry tends to use Doofenshmirtz 's inventions to erase evidence of whatever contraptions Phineas and Ferb had made , leaving Candace unable to bust them . Examples include when Perry asked to borrow Doofenshmirtz 's robot Norm to pick up footage from the city surveillance cameras in order to preserve his job as an agent , as well as using Doofenshmirtz 's Pick @-@ Him @-@ Up @-@ inator to rescue a lost Candace and bring her home .

Perry and Doofenshmirtz at first seem to loathe each other in the beginning of the series , and have been arch @-@ nemeses since the day they met . However , they <a href='drop_aux' title='1'><mark>are</mark></a>often cordial and friendly towards one another and it is said by Doofenshmirtz that Perry is his best friend , and Perry will often act to save Doofenshmirtz <a href='null_genetive' title='2'><mark>'s</mark></a>life when his plot inevitably <a href='uninflect' title='3'><mark>blows</mark></a> up in his face . Habitually , their daily brawls involve Doofenshmirtz devising a scheme , which Perry <a href='uninflect' title='4'><mark>goes</mark></a> to stop after being briefed by Major Monogram . He is trapped by Doofenshmirtz while trying to do so and is told of the doctor <a href='null_genetive' title='5'><mark>'s</mark></a>scheme , usually pertaining to some backstory or pet peeve . He then <a href='uninflect' title='6'><mark>escapes</mark></a> and the two fight , Perry coming out victorious . The two rely on this daily structure , Doofenshmirtz even specifically mentioning it in " Journey to the Center of Candace " and in episodes such as " It 's About Time ! " in which Doofenshmirtz temporarily <a href='uninflect' title='7'><mark>replaces</mark></a> Perry with secret agent Peter The Panda and they become depressed about not having each other to fight . Perry <a href='uninflect' title='8'><mark>realizes</mark></a> he <a href='uninflect' title='9'><mark>misses</mark></a> Doof too . When Perry <a href='uninflect' title='10'><mark>does</mark></a> not arrive on <a href='None' title='11'><mark>the</mark></a><a href='negative_concord' title='12'><mark>scene</mark></a> of Doofenshmirtz <a href='null_genetive' title='13'><mark>'s</mark></a>evil plan , the doctor <a href='uninflect' title='14'><mark>hesitates</mark></a> to execute his plans and fears for where Perry <a href='been_done' title='15'><mark>has</mark></a> gone , though he <a href='uninflect' title='16'><mark>notes</mark></a> that he " <a href='uninflect' title='17'><mark>hopes</mark></a> something terrible <a href='been_done' title='18'><mark>has</mark></a> happened to him . " . Sometimes , they decided not to fight and <a href='got' title='19'><mark>have</mark></a> fun , as shown in " Happy New Year ! " and " Candace Disconnected " . On other occasions , depending on whatever situation Doofenshmirtz is facing , Perry would often help Doofenshmirtz with his non @-@ evil plans , such as helping him overcome evil scientist <a href='null_genetive' title='20'><mark>'s</mark></a>block , helping him put on a birthday party for his 16 @-@ year @-@ old daughter Vanessa , impressing a square dancing girl with programmable square dancing boots <a href='null_relcl' title='21'><mark>that</mark></a>Doofenshmritz created , working together to stop a raging platypus hunter from hunting them down , or helping him convince his rich ex @-@ wife to help pay off his mortgage debt . Also , Perry <a href='uninflect' title='22'><mark>tends</mark></a> to use Doofenshmirtz <a href='null_genetive' title='23'><mark>'s</mark></a>inventions to erase evidence of whatever contraptions Phineas and Ferb <a href='been_done' title='24'><mark>had</mark></a> made , leaving Candace unable to bust them . Examples include when Perry asked to borrow Doofenshmirtz <a href='null_genetive' title='25'><mark>'s</mark></a>robot Norm to pick up footage from the city surveillance cameras in order to preserve his job as an agent , as well as using Doofenshmirtz <a href='null_genetive' title='26'><mark>'s</mark></a>Pick @-@ Him @-@ Up @-@ inator to rescue a lost Candace and bring her home .

Perry and Doofenshmirtz at first seem to loathe each other in da beginning of tdaseries , and have been arch @-@ nemeses since thdaay they met . However , they often cordial and friendly towards one anotha and it is said by Doofenshmirtz that Perry is his best homie , and Perry gon often act to save Doofenshmirtz life when his plot inevitably blow up in his face . Habitually , their daily brawls involve Doofenshmirtz devising a scheme , which Perry go to stop after being briefed by Major Monogram . He is trapped by Doofenshmirtz while tryna do so and is tld of the doctor scheme , usually pertaining to sum backstory or pet peeve . He then escape and the two fight , Perry coming out victorious . Thedao rely on this daily structure , Doofenshmirtz even specifically mentioning it in " Journey to the dater of Candace " and in episodes such as " It 's About Time ! " in which Doofenshmirtz temporarily replace Perry with secret agent Peter The Panda and they become depressed about not havin each other to fight . Perry kno he miss Doof too . When Perry do not arrive on no scene of Doofenshmirtz evil plan , the ddaor hesitate to execute his plans and fears fir where Perry done gone , though he note that he " hope somthing terrible done happened to em . " . Sometimes , they decided not to fight and got fun , as shown in " Happy New Year ! " and " Candace Disconnected " . On other occasions , depending on whatever shyt Doofenshmirtz is facing , Perry would often help Doofenshmirtz with his non @-@ evil plans , such as helping him overcome evil scientist block , helping him put on a birthday party for his 16 @-@ year @-@ old daughter Vanessa , impressing a square dancing gurl with programmable square dancing boots Doofenshmritz created , working together to stop a raging platypus hunter from hunting em dwn , or helpin hemconvince his rich ex @-@ wife to help pay offf his mortgage debt . Also , Perry tend to use Doofenshmirtz inventions to erase evidence of whatever contraptions Phineas and Ferb done made , leavin Candace unable to bust them . Examples include when Perry asked to borrow Doofenshmirtz robot Norm to pick up footage from the cidasurveillance cameras in order to preserve his job as an agent , as well as using Doofenshmirtz Pick @-@ Him @-@ Up @-@ inator to rescue a lost Candace and bring her home .

In Phineas and Ferb the Movie : Across the 2nd Dimension , an alternate reality ( yet more evil and ruthless ) version of Perry ( known as Platyborg ) appears as the secondary antagonist , with the regular Perry serving as a supporting protagonist . Platyborg would later return in the episode sequel , Tales from the Resistance : Back to the 2nd Dimension , this time , as a supporting protagonist .

In Phineas and Ferb the Movie : Across the 2nd Dimension , an alternate reality ( yet more evil and ruthless ) version of Perry ( known as Platyborg ) <a href='uninflect' title='1'><mark>appears</mark></a> as the secondary antagonist , with the regular Perry serving as a supporting protagonist . Platyborg would later return in the episode sequel , Tales from the Resistance : Back to the 2nd Dimension , this time , as a supporting protagonist .

In Phineas and Ferb da Movie : Across the 2nd Dimension , an alternate reality ( yet more evil and ruthless ) version of Perry ( known as Platyborg ) appear as the secondary antagonist , with tdaregular Perry serving as a supporting protagonist . Platyborg would later return in thdapisode sequel , Tales from thedasistance : bacc to the 2nd Dimension , dis time , as a supporting protagonist .

= = Character = =

= = Character = =

= = Character = =

= = = Creation and conception = = =

= = = Creation and conception = = =

= = = Creation and conception = = =

While working on the animated television series Rocko 's Modern Life , Phineas and Ferb co @-@ founders Dan Povenmire and Jeff " Swampy " Marsh utilized several recurring elements in the episodes that they wrote . Among these were actions sequences and chase scenes . Povenmire and Marsh wanted to reuse these elements in their series and chose Perry to execute it . The pair gave him a consistent and continuous nemesis in the form of Doofenshmirtz as a means of allowing viewers to get to know him .

While working on the animated television series Rocko <a href='null_genetive' title='1'><mark>'s</mark></a>Modern Life , Phineas and Ferb <a href='uninflect' title='2'><mark>co</mark></a> @-@ <a href='uninflect' title='3'><mark>founders</mark></a> Dan Povenmire and Jeff " Swampy " Marsh utilized several recurring elements in the episodes that they wrote . Among these <a href='uninflect' title='4'><mark>were</mark></a> actions sequences and chase scenes . Povenmire and Marsh wanted to reuse these elements in their series and chose Perry to execute it . The pair gave him a consistent and continuous nemesis in the form of Doofenshmirtz as a means of allowing viewers to get to know him .

While working on da animated television series Rocko Modern Life , Phineas and Ferb coed @-@ founder Dan Povenmire and Jeff " Swampy " Marsh utilized several recurring elements in the episodes that they wrote . Among these was actions sequences and chase scenes . Povenmire and Marsh wanted to reuse these elements in their series and chose Perry to execute it . The pair gave em a consistent and continuous nemesis in tdaform of Doofenshmirtz as a means of allowing viewers to get to know hem.

While choosing a species for Perry , Povenmire and Marsh wanted to keep in mind selecting one that was uncommon , an animal that kids could not " pick out at a pet store and beg [ their parents ] for . " They chose a platypus because of the animal 's obscure and striking appearance . The animal was scarcely used in American animated programs , so the pair opined that Perry " would not have to compete with preconceived notions that viewers might bring to a more conventional critter . " The blank storyboard they were given allowed them to " make stuff up " since " no one knows very much about [ them ] . "

While choosing a species for Perry , Povenmire and Marsh wanted to keep in mind selecting one <a href='null_relcl' title='1'><mark>that</mark></a>was uncommon , an animal <a href='null_relcl' title='2'><mark>that</mark></a>kids could not " pick out at a pet store and beg [ their parents ] for . " They chose a platypus because of the animal <a href='null_genetive' title='3'><mark>'s</mark></a>obscure and striking appearance . The animal was scarcely used in American animated programs , so the pair opined that Perry " would not have to compete with preconceived notions <a href='null_relcl' title='4'><mark>that</mark></a>viewers might bring to a more conventional critter . " The blank storyboard they <a href='uninflect' title='5'><mark>were</mark></a> given allowed them to " make stuff up " since " no one <a href='uninflect' title='6'><mark>knows</mark></a> very much about [ them ] . "

While choosing a species for Perry , Povenmire and Marsh wanted to keep in mind selecting one was uncommon , an animal kids could not " pick out at a pet store and beg [ their parents ] for . " They chose a platypus cuz of da animal obscure and striking appearance . The animal was scarcely used in American animated programs , so the pair opined that Perry " would not gotta compete w preconceived notions viewers might bring to a more conventional critter . " The blank storyboard they was given allowed them to " make shii up " since " no one know very much about [ em ] . "

Perry has a theme song tentatively entitled " Perry , " performed by Randy Crenshaw and Laura Dickinson , and written by Povenmire and Marsh , who write the majority of songs in the series . The song , along with the number " Gitchee Gitchee Goo " from the episode " Flop Starz , " was the first musical composition Povenmire and Marsh pitched to The Walt Disney Company . They were nervous doing so , because , as Povenmire explained , " Disney has a big history of music -- what if they hate it ? " Their reaction , however , was considerably positive and the pair was asked to write a song for each episode , which they vehemently agreed to . The opening lyrics for the song describe Perry as a standard textbook definition of a platypus : " He 's a semi @-@ aquatic egg @-@ laying mammal of action . "

Perry <a href='got' title='1'><mark>has</mark></a> a theme song tentatively entitled " Perry , " performed by Randy Crenshaw and Laura Dickinson , and written by Povenmire and Marsh , <a href='null_relcl' title='2'><mark>who</mark></a>write the majority of songs in the series . The song , along with the number " Gitchee Gitchee Goo " from the episode " Flop Starz , " was the first musical composition Povenmire and Marsh pitched to The Walt Disney Company . They <a href='uninflect' title='3'><mark>were</mark></a> nervous doing so , because , as Povenmire explained , " Disney <a href='got' title='4'><mark>has</mark></a> a big history of music -- what if they hate it ? " Their reaction , however , was considerably positive and the pair was asked to write a song for each episode , which they vehemently agreed to . The opening lyrics for the song describe Perry as a standard textbook definition of a platypus : " He 's a semi @-@ aquatic egg @-@ laying mammal of action . "

Perry got a theme song tentatively entitled " Perry , " performed by Randy Crenshaw and Laura Dickinson , and written by Povenmire and Marsh , write da majority of songs in tdaseries . The song , along with thdaumber " Gitchee Gitchee Goo " from thedaisode " Flop Starz , " was the dast musical composition Povenmire and Marsh pitched to The Wda Disney Company . They was nervous doing soo , because , as Povenmire explained , " Disney got a big history of music -- wht if they hate it ? " Their reaction , however , was considerably positive and the padawas asked to write a song fir each episode , which they vehemently agreed to . The opening lyrics for the song describe Perry as a standard textbook definition of a platypus : " He 's a semi @-@ aquatic egg @-@ laying mammal of action . "

= = = Design = = =

= = = Design = = =

= = = Design = = =

Like the other characters of the series , Perry was structured in a simple style to allow young viewers to easily draw him . In keeping with the show 's general design scheme , Perry is constructed of geometric shapes in a style reminiscent of deceased Looney Tunes animator Tex Avery . Povenmire uses different design styles for drawing Perry depending on how he is portrayed . When Perry is portrayed as a domesticated and mindless pet , Povenmire begins with a square shaped like a loaf of bread . He then draws his front legs and feet before drawing his bill , which is set at a certain angle . Povenmire then draws his eyeballs , which are never focused and look in opposing directions in a daze . He concludes the figure by adding his hind legs , tail , hair , and finally color .

Like the other characters of the series , Perry was structured in a simple style to allow young viewers to easily draw him . In keeping with the show <a href='null_genetive' title='1'><mark>'s</mark></a>general design scheme , Perry is constructed of geometric shapes in a style reminiscent of deceased Looney Tunes animator Tex Avery . Povenmire <a href='uninflect' title='2'><mark>uses</mark></a> different design styles for drawing Perry depending on how he is portrayed . When Perry is portrayed as a domesticated and mindless pet , Povenmire <a href='uninflect' title='3'><mark>begins</mark></a> with a square shaped like a loaf of bread . He then <a href='uninflect' title='4'><mark>draws</mark></a> his front legs and feet before drawing his bill , which is set at a certain angle . Povenmire then <a href='uninflect' title='5'><mark>draws</mark></a> his eyeballs , which <a href='negative_concord' title='6'><mark>are</mark></a> <a href='negative_concord' title='7'><mark>never</mark></a> focused and look in opposing directions in a daze . He <a href='uninflect' title='8'><mark>concludes</mark></a> the figure by adding his hind legs , tail , hair , and finally color .

Like the other characters of the series , Perry was structured in a simple style to allow young viewers to easily draw him . In keepin with the show general design scheme , Perry is constructed of geometric shapes in a style reminiscent of deceased Looney Tunes animator Tex Avery . Povenmire use diff design styles for drawing Perry depending on how he is portrayed . When Perry is portrayed as a domesticated and mindless pet , Povenmire begin wit a square shaped like a loaf of bread . He then draw his front legs and feet before drawing his bill , which is set at a certain angle . Povenmire then draw his eyeballs , which ain't never focused and look in opposing directions in a daze . He conclude da figure by adding his hind legs , tail , hair , and finally color .

When portrayed as a secret agent , Povenmire starts with a similar bread loaf square design , but draws it standing up vertically and places a fedora on the top of his head , which is combined with the square torso . In contrast to his mindless and wild @-@ eyed expression as a pet , the secret agent version of Perry is detailed with eyes " full of steely blue resolve . " Povenmire proceeds by drawing his arms , which bear hands that are open and prepared for fighting or any danger . His legs are bent , as well prepared for an act of danger or action needed . Povenmire finishes the design by adding his beaver tail and color .

When portrayed as a secret agent , Povenmire <a href='uninflect' title='1'><mark>starts</mark></a> with a similar bread loaf square design , but <a href='uninflect' title='2'><mark>draws</mark></a> it standing up vertically and <a href='uninflect' title='3'><mark>places</mark></a> a fedora on the top of his head , which is combined with the square torso . In contrast to his mindless and wild @-@ eyed expression as a pet , the secret agent version of Perry is detailed with eyes " full of steely blue resolve . " Povenmire <a href='uninflect' title='4'><mark>proceeds</mark></a> by drawing his arms , which bear hands <a href='null_relcl' title='5'><mark>that</mark></a><a href='drop_aux' title='6'><mark>are</mark></a>open and prepared for fighting or any danger . His legs <a href='drop_aux' title='7'><mark>are</mark></a>bent , as well prepared for an act of danger or action needed . Povenmire <a href='uninflect' title='8'><mark>finishes</mark></a> the design by adding his beaver tail and color .

When portrayed as a secret agent , Povenmire start w/ a similar bread loaf square design , but draw it standin up vertically and place a fedora on the top of his head , which is combined wiw/he square torso . In contrast to his mindless and wild @-@ eyed expression as a pet , the secret agent version of Perry is detailed withw/s " full of steely blue resolve . " Povenmire proceed by drawing his arms , which bear hands open and prepared fa fightin or any danger . His legs bent , as well prepared ffiran act of danger or action needed . Povenmire finish da design by adding his beaver tail and color .