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Sun rotation difference (equator/latitude/pole)?

  1. Feb 21, 2008 #1
    I just learned the sun has an equatorial rotation rate of approximately 25 earth days, and a polar rotation of approximately 31 days.

    Intuitively, by the laws of physics, it should be the other way around: longer at the equator and shorter at the poles?

    Also, if our solar system is within a larger orbit, is there a year for the sun in that orbit?

    What I read is in terms of our year here on Earth - not that there is anything wrong with the Earth year, of course.

    I love the year here on Earth.

    Any light cast on my shadow is, in advance, very much appreciated.
     
  2. jcsd
  3. Feb 21, 2008 #2
    I'm sure there are others on this board who can explain to you the exact mechanism in GREAT detail (eg., spacetiger), but I'll just stick with the obvious superficial answers to start off :)

    You're referring to the sun's "differential rotation" which occurs because the sun is not a big solid ball (it's plasma... super hot ionized gas), different parts rotate at different angular velocities.

    This differential rotation applies to other gaseous bodies like the Jovian planets, as well as the disk of the galaxy.

    If I understand you, you are asking: does the sun itself orbit another body in space?

    If that's what you are asking then the answer is YES. Our sun revolves around the galactic center at about 220 km/s, and it takes one "galactic year", or approximately 220 MILLION earth-years, to orbit. Interestingly enough, that's a supermassive BLACK HOLE that the sun is orbiting around!
     
    Last edited: Feb 21, 2008
  4. Feb 23, 2008 #3
    Follow-up question on galactic year and shape

    Thank you for answering my questions. I appreciate your patience.

    What shape is the sun (i.e. shape consistent with the rotation times)?

    It should be wider at the poles than at the equator, correct?

    Yes, exactly what I wanted to know.

    My next question is a follow-up question on the time of "galactic year" = 220 million earth-years.

    Is time always relative to time here on Earth and/or in our solar system?
     
  5. Feb 24, 2008 #4

    Chronos

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    The sun is a plasma ball, as mentioned, it rotates differentially like a fluid.
     
  6. Feb 24, 2008 #5
    As Chronos pointed out, the sun is shaped like a ball (a SLIGHTLY flattened ball).

    If you are asking if the sun's "polar radius" is larger than the "equatorial radius", then the answer is NO -- it's actually the other way around. Due to the centrifugal effect of the sun rotating on its axis, the equator is SLIGHTLY bulging out. But this difference between the polar radius and the equatorial radius is VERY VERY small -- only about 5 miles or so [1] (which is insignificant given the radius of the sun -- over 400,000 miles). So, for all intents and purposes, the sun is basically a big ball.

    A really good website if you want to learn more about the sun is "this site (The nine planets)."
    If I understand your question correctly, then YES, time is given in Earth years (or months or days, etc.), unless otherwise stated. So when the author of that link I gave you above says, "at the equator the surface rotates once every 25.4 days; near the poles it's as much as 36 days", he means EARTH days.

    Hope that helps!

    [1] Godier, S., Rozelot J.-P. (2000) Astronomy and Astrophysics 355: 365–374.
     
  7. Feb 28, 2008 #6
    Suns apparent differential rotation

    Hi Drewterry:

    I may not be of much help on this but there is common belief amoung astronomers (which I am not) that the Sun exibits differential rotation. This to discribe the observation that the Sun's equator rotates faster than the balance of the Sun as you travel towards the poles.

    Just looking at the Sun the surface is quite uniform except for the Sun Spots that show up black. The measurement of the Sun's rotation is usualy dependent on the observation of the Sun spot movement and that observation does fully support the conclusion.

    I do not know of any clear cut explanation for why the Sun, or Jupiter for that matter as cited in a earlier reply, would exibit differential rotation. If it was due to the drag of the planets on the Sun it should not be so wide spread because the planets are pretty close to the eliptic. Perhaps the pull of the planets are slowing down the suns rotation so the equatorial area rotates slower. Keep in mind the size of the Sun incomparison to the planets. It appears unlikely the tiny specks could effect the Sun's rotation, but we do not know for sure.

    Another possibility, for which there is no proof at all, is that the very large size of the Sun causes the poles to be 432,000 miles farther from the equator when the sunlight we see is sent on its way. That means it will take the sunlight a wee bit longer to catch up with the light from the equator and may cause a visual effect simulating the different visual effects on rotation. One thing that interests me about this is that the degree of differential rotation we see migrates uniformly from the equator to the poles just as the shape of a sphere causes each step of the way to be farther and farther away.

    I do not wish to confuse you so recall this last comment has no documentation. It is simply fun to consider other prospects when proof positive is lacking.
     
    Last edited: Feb 28, 2008
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