Why does the Sun have different day lengths, but not the gas giants?












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The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force works, the equator must move faster than the poles.



Question: if this works, why do Jupiter/Saturn/Uranus/Neptune have well-defined days? Why don't the equators of these planets rotate faster than the poles as well? For example, Wikipedia's article on Jupiter gives the length of a Jovian day as 9h 55m 30s, which is so precise that it implies Jupiter does not have a rotational period which varies with latitude.










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    8












    $begingroup$


    The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force works, the equator must move faster than the poles.



    Question: if this works, why do Jupiter/Saturn/Uranus/Neptune have well-defined days? Why don't the equators of these planets rotate faster than the poles as well? For example, Wikipedia's article on Jupiter gives the length of a Jovian day as 9h 55m 30s, which is so precise that it implies Jupiter does not have a rotational period which varies with latitude.










    share|improve this question









    $endgroup$















      8












      8








      8





      $begingroup$


      The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force works, the equator must move faster than the poles.



      Question: if this works, why do Jupiter/Saturn/Uranus/Neptune have well-defined days? Why don't the equators of these planets rotate faster than the poles as well? For example, Wikipedia's article on Jupiter gives the length of a Jovian day as 9h 55m 30s, which is so precise that it implies Jupiter does not have a rotational period which varies with latitude.










      share|improve this question









      $endgroup$




      The Sun's rotation period varies from about 25 days at the equator to about 38 days at the poles. As I understand it, this is because the Sun is not solid, and because of the way centripetal force works, the equator must move faster than the poles.



      Question: if this works, why do Jupiter/Saturn/Uranus/Neptune have well-defined days? Why don't the equators of these planets rotate faster than the poles as well? For example, Wikipedia's article on Jupiter gives the length of a Jovian day as 9h 55m 30s, which is so precise that it implies Jupiter does not have a rotational period which varies with latitude.







      the-sun rotation gas-giants






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      asked 2 hours ago









      AllureAllure

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          $begingroup$

          It's a matter of how "day" is defined.



          Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:




          The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)




          The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.



          We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.






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            9












            $begingroup$

            It's a matter of how "day" is defined.



            Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:




            The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)




            The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.



            We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.






            share|improve this answer









            $endgroup$


















              9












              $begingroup$

              It's a matter of how "day" is defined.



              Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:




              The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)




              The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.



              We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.






              share|improve this answer









              $endgroup$
















                9












                9








                9





                $begingroup$

                It's a matter of how "day" is defined.



                Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:




                The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)




                The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.



                We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.






                share|improve this answer









                $endgroup$



                It's a matter of how "day" is defined.



                Wikipedia's article on Jupiter cites this IAU/IAG paper for the length of a Jupiter day. In it, footnote (e) of table I has the following:




                The equations for W for Jupiter, Saturn, Uranus and Neptune refer to the rotation of their magnetic fields (System III)




                The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed. This produces a periodic variation in the radio emissions of the planet, which is used to measure the rotation speed of that object.



                We're reasonably certain the Sun doesn't have a coherent core, so measuring the rotation speed of the magnetic field doesn't provide a useful definition of the Sun's rotation speed.







                share|improve this answer












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                share|improve this answer










                answered 2 hours ago









                MarkMark

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                1,649619






























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