I know that at the equator at 0 degrees latitude , you could track a sunspot and then use T=2pi/w and w=∆theta/∆t to work out the period the equator rotates, but how would you do it for, say, sunspots/regions near the poles?

  • $\begingroup$ Maybe I am missing the point, but what's wrong with doing it the same way for higher latitudes? If you want to observe very close to the pole, you may need a solar observatory satellite in a (close to) polar orbit around the sun, of course. $\endgroup$
    – CuriousOne
    Oct 10, 2014 at 21:57
  • $\begingroup$ Hmm..for sunspot near the equator, I would've used pi radians as the change in angle- near the poles it wouldn't be pi radians when you observe a sunspot going from one side to the other..? $\endgroup$
    – user58953
    Oct 10, 2014 at 22:40
  • $\begingroup$ Ah! Are you hung up on the definition of radians? I agree, that is somewhat confusing. The wikipedia entry (en.wikipedia.org/wiki/Radian) defines it as: "Radian describes the plane angle subtended by a circular arc as the length of the arc divided by the radius of the arc". In order to express the angular motion of a sunspot in radian, you have to divide the physical distance that the sunspot moves by the radius of the slice of the sun that it moves around at that latitude. So $2\pi$ radian is always 360 degrees, $\pi$ radian is 180, except for the pole where the radius is zero. $\endgroup$
    – CuriousOne
    Oct 11, 2014 at 0:37
  • $\begingroup$ Or you could just wait until the spot crossed the same longitude line again. A more pressing problem is that there are no sunspots near the solar rotation pole! $\endgroup$
    – ProfRob
    Oct 11, 2014 at 8:34
  • $\begingroup$ If you know the change in latitude/longitude of a sunspot, is there a formula you can plug it into to find the period? $\endgroup$
    – user58953
    Oct 11, 2014 at 15:14


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