 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 .