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












38












$begingroup$


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









$endgroup$

















    38












    $begingroup$


    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









    $endgroup$















      38












      38








      38


      1



      $begingroup$


      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






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Mar 22 at 2:38









      AllureAllure

      582311




      582311






















          1 Answer
          1






          active

          oldest

          votes


















          49












          $begingroup$

          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 radio emissions of the gas giants have well-defined periodic variations. These variations are caused by the rotation of the magnetic fields of those planets, and are evidence that they have a reasonably coherent core of some sort that's rotating at a uniform speed. The periodic variations then represent the rotation speed of that object, which is taken as the rotation speed of the planet.



          We're reasonably certain the Sun doesn't have a coherent core. Measuring the variation of the magnetic field doesn't show a well-defined period, and doesn't provide a useful definition of the Sun's rotation speed.






          share|improve this answer











          $endgroup$









          • 4




            $begingroup$
            I just add that for Jupiter there is definitively no a fix day based on std rotation. At least no for the outer layer. It does even rotate in stripes and a simulation as in Celestia package is a kind of spectacle.
            $endgroup$
            – Alchimista
            Mar 22 at 8:08








          • 6




            $begingroup$
            “The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed.” — I’d strengthen this by pointing out that it’s not just an assumption, it’s based closely on empirical facts: the magnetic field has a measurable uniform periodic behaviour, and based our understanding of planetary magnetic fields, we’re confident this corresponds to rotation of a somewhat coherent core. With the sun, as I understand it, we don’t see any uniformly periodic behaviour that we would expect to correspond to some kind of rotating mass.
            $endgroup$
            – Peter LeFanu Lumsdaine
            Mar 22 at 13:37






          • 1




            $begingroup$
            The Sun's magnetic field don't have a period as @PeterLeFanuLumsdaine stated.
            $endgroup$
            – Mindwin
            Mar 22 at 14:06











          Your Answer





          StackExchange.ifUsing("editor", function () {
          return StackExchange.using("mathjaxEditing", function () {
          StackExchange.MarkdownEditor.creationCallbacks.add(function (editor, postfix) {
          StackExchange.mathjaxEditing.prepareWmdForMathJax(editor, postfix, [["$", "$"], ["\\(","\\)"]]);
          });
          });
          }, "mathjax-editing");

          StackExchange.ready(function() {
          var channelOptions = {
          tags: "".split(" "),
          id: "514"
          };
          initTagRenderer("".split(" "), "".split(" "), channelOptions);

          StackExchange.using("externalEditor", function() {
          // Have to fire editor after snippets, if snippets enabled
          if (StackExchange.settings.snippets.snippetsEnabled) {
          StackExchange.using("snippets", function() {
          createEditor();
          });
          }
          else {
          createEditor();
          }
          });

          function createEditor() {
          StackExchange.prepareEditor({
          heartbeatType: 'answer',
          autoActivateHeartbeat: false,
          convertImagesToLinks: false,
          noModals: true,
          showLowRepImageUploadWarning: true,
          reputationToPostImages: null,
          bindNavPrevention: true,
          postfix: "",
          imageUploader: {
          brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
          contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
          allowUrls: true
          },
          noCode: true, onDemand: true,
          discardSelector: ".discard-answer"
          ,immediatelyShowMarkdownHelp:true
          });


          }
          });














          draft saved

          draft discarded


















          StackExchange.ready(
          function () {
          StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fastronomy.stackexchange.com%2fquestions%2f30087%2fwhy-does-the-sun-have-different-day-lengths-but-not-the-gas-giants%23new-answer', 'question_page');
          }
          );

          Post as a guest















          Required, but never shown

























          1 Answer
          1






          active

          oldest

          votes








          1 Answer
          1






          active

          oldest

          votes









          active

          oldest

          votes






          active

          oldest

          votes









          49












          $begingroup$

          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 radio emissions of the gas giants have well-defined periodic variations. These variations are caused by the rotation of the magnetic fields of those planets, and are evidence that they have a reasonably coherent core of some sort that's rotating at a uniform speed. The periodic variations then represent the rotation speed of that object, which is taken as the rotation speed of the planet.



          We're reasonably certain the Sun doesn't have a coherent core. Measuring the variation of the magnetic field doesn't show a well-defined period, and doesn't provide a useful definition of the Sun's rotation speed.






          share|improve this answer











          $endgroup$









          • 4




            $begingroup$
            I just add that for Jupiter there is definitively no a fix day based on std rotation. At least no for the outer layer. It does even rotate in stripes and a simulation as in Celestia package is a kind of spectacle.
            $endgroup$
            – Alchimista
            Mar 22 at 8:08








          • 6




            $begingroup$
            “The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed.” — I’d strengthen this by pointing out that it’s not just an assumption, it’s based closely on empirical facts: the magnetic field has a measurable uniform periodic behaviour, and based our understanding of planetary magnetic fields, we’re confident this corresponds to rotation of a somewhat coherent core. With the sun, as I understand it, we don’t see any uniformly periodic behaviour that we would expect to correspond to some kind of rotating mass.
            $endgroup$
            – Peter LeFanu Lumsdaine
            Mar 22 at 13:37






          • 1




            $begingroup$
            The Sun's magnetic field don't have a period as @PeterLeFanuLumsdaine stated.
            $endgroup$
            – Mindwin
            Mar 22 at 14:06
















          49












          $begingroup$

          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 radio emissions of the gas giants have well-defined periodic variations. These variations are caused by the rotation of the magnetic fields of those planets, and are evidence that they have a reasonably coherent core of some sort that's rotating at a uniform speed. The periodic variations then represent the rotation speed of that object, which is taken as the rotation speed of the planet.



          We're reasonably certain the Sun doesn't have a coherent core. Measuring the variation of the magnetic field doesn't show a well-defined period, and doesn't provide a useful definition of the Sun's rotation speed.






          share|improve this answer











          $endgroup$









          • 4




            $begingroup$
            I just add that for Jupiter there is definitively no a fix day based on std rotation. At least no for the outer layer. It does even rotate in stripes and a simulation as in Celestia package is a kind of spectacle.
            $endgroup$
            – Alchimista
            Mar 22 at 8:08








          • 6




            $begingroup$
            “The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed.” — I’d strengthen this by pointing out that it’s not just an assumption, it’s based closely on empirical facts: the magnetic field has a measurable uniform periodic behaviour, and based our understanding of planetary magnetic fields, we’re confident this corresponds to rotation of a somewhat coherent core. With the sun, as I understand it, we don’t see any uniformly periodic behaviour that we would expect to correspond to some kind of rotating mass.
            $endgroup$
            – Peter LeFanu Lumsdaine
            Mar 22 at 13:37






          • 1




            $begingroup$
            The Sun's magnetic field don't have a period as @PeterLeFanuLumsdaine stated.
            $endgroup$
            – Mindwin
            Mar 22 at 14:06














          49












          49








          49





          $begingroup$

          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 radio emissions of the gas giants have well-defined periodic variations. These variations are caused by the rotation of the magnetic fields of those planets, and are evidence that they have a reasonably coherent core of some sort that's rotating at a uniform speed. The periodic variations then represent the rotation speed of that object, which is taken as the rotation speed of the planet.



          We're reasonably certain the Sun doesn't have a coherent core. Measuring the variation of the magnetic field doesn't show a well-defined period, and 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 radio emissions of the gas giants have well-defined periodic variations. These variations are caused by the rotation of the magnetic fields of those planets, and are evidence that they have a reasonably coherent core of some sort that's rotating at a uniform speed. The periodic variations then represent the rotation speed of that object, which is taken as the rotation speed of the planet.



          We're reasonably certain the Sun doesn't have a coherent core. Measuring the variation of the magnetic field doesn't show a well-defined period, and doesn't provide a useful definition of the Sun's rotation speed.







          share|improve this answer














          share|improve this answer



          share|improve this answer








          edited Mar 22 at 19:55

























          answered Mar 22 at 3:14









          MarkMark

          1,874920




          1,874920








          • 4




            $begingroup$
            I just add that for Jupiter there is definitively no a fix day based on std rotation. At least no for the outer layer. It does even rotate in stripes and a simulation as in Celestia package is a kind of spectacle.
            $endgroup$
            – Alchimista
            Mar 22 at 8:08








          • 6




            $begingroup$
            “The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed.” — I’d strengthen this by pointing out that it’s not just an assumption, it’s based closely on empirical facts: the magnetic field has a measurable uniform periodic behaviour, and based our understanding of planetary magnetic fields, we’re confident this corresponds to rotation of a somewhat coherent core. With the sun, as I understand it, we don’t see any uniformly periodic behaviour that we would expect to correspond to some kind of rotating mass.
            $endgroup$
            – Peter LeFanu Lumsdaine
            Mar 22 at 13:37






          • 1




            $begingroup$
            The Sun's magnetic field don't have a period as @PeterLeFanuLumsdaine stated.
            $endgroup$
            – Mindwin
            Mar 22 at 14:06














          • 4




            $begingroup$
            I just add that for Jupiter there is definitively no a fix day based on std rotation. At least no for the outer layer. It does even rotate in stripes and a simulation as in Celestia package is a kind of spectacle.
            $endgroup$
            – Alchimista
            Mar 22 at 8:08








          • 6




            $begingroup$
            “The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed.” — I’d strengthen this by pointing out that it’s not just an assumption, it’s based closely on empirical facts: the magnetic field has a measurable uniform periodic behaviour, and based our understanding of planetary magnetic fields, we’re confident this corresponds to rotation of a somewhat coherent core. With the sun, as I understand it, we don’t see any uniformly periodic behaviour that we would expect to correspond to some kind of rotating mass.
            $endgroup$
            – Peter LeFanu Lumsdaine
            Mar 22 at 13:37






          • 1




            $begingroup$
            The Sun's magnetic field don't have a period as @PeterLeFanuLumsdaine stated.
            $endgroup$
            – Mindwin
            Mar 22 at 14:06








          4




          4




          $begingroup$
          I just add that for Jupiter there is definitively no a fix day based on std rotation. At least no for the outer layer. It does even rotate in stripes and a simulation as in Celestia package is a kind of spectacle.
          $endgroup$
          – Alchimista
          Mar 22 at 8:08






          $begingroup$
          I just add that for Jupiter there is definitively no a fix day based on std rotation. At least no for the outer layer. It does even rotate in stripes and a simulation as in Celestia package is a kind of spectacle.
          $endgroup$
          – Alchimista
          Mar 22 at 8:08






          6




          6




          $begingroup$
          “The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed.” — I’d strengthen this by pointing out that it’s not just an assumption, it’s based closely on empirical facts: the magnetic field has a measurable uniform periodic behaviour, and based our understanding of planetary magnetic fields, we’re confident this corresponds to rotation of a somewhat coherent core. With the sun, as I understand it, we don’t see any uniformly periodic behaviour that we would expect to correspond to some kind of rotating mass.
          $endgroup$
          – Peter LeFanu Lumsdaine
          Mar 22 at 13:37




          $begingroup$
          “The assumption is that whatever's generating the magnetic field forms a reasonably coherent mass that's rotating at a uniform speed.” — I’d strengthen this by pointing out that it’s not just an assumption, it’s based closely on empirical facts: the magnetic field has a measurable uniform periodic behaviour, and based our understanding of planetary magnetic fields, we’re confident this corresponds to rotation of a somewhat coherent core. With the sun, as I understand it, we don’t see any uniformly periodic behaviour that we would expect to correspond to some kind of rotating mass.
          $endgroup$
          – Peter LeFanu Lumsdaine
          Mar 22 at 13:37




          1




          1




          $begingroup$
          The Sun's magnetic field don't have a period as @PeterLeFanuLumsdaine stated.
          $endgroup$
          – Mindwin
          Mar 22 at 14:06




          $begingroup$
          The Sun's magnetic field don't have a period as @PeterLeFanuLumsdaine stated.
          $endgroup$
          – Mindwin
          Mar 22 at 14:06


















          draft saved

          draft discarded




















































          Thanks for contributing an answer to Astronomy Stack Exchange!


          • Please be sure to answer the question. Provide details and share your research!

          But avoid



          • Asking for help, clarification, or responding to other answers.

          • Making statements based on opinion; back them up with references or personal experience.


          Use MathJax to format equations. MathJax reference.


          To learn more, see our tips on writing great answers.




          draft saved


          draft discarded














          StackExchange.ready(
          function () {
          StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fastronomy.stackexchange.com%2fquestions%2f30087%2fwhy-does-the-sun-have-different-day-lengths-but-not-the-gas-giants%23new-answer', 'question_page');
          }
          );

          Post as a guest















          Required, but never shown





















































          Required, but never shown














          Required, but never shown












          Required, but never shown







          Required, but never shown

































          Required, but never shown














          Required, but never shown












          Required, but never shown







          Required, but never shown







          Popular posts from this blog

          Plaza Victoria

          Puebla de Zaragoza

          Musa