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    Re: Sun goes round Earth, or something like that...
    From: Alexandre Eremenko
    Date: 2014 Feb 16, 18:39 -0500

    Frank,
    
    Your explanation oversimplifies the matter:-)
    
    > Can't
    > we say that it's just the same as the Sun revolving around the Earth since
    > all motion is relative?? The answer is 'no' because the premise is wrong.
    > It's not true that ALL motion is relative.
    
    In some sense it IS true. If you allow non-uniform motions.
    To say that Sun rotates about earth is correct (and Nautical almanac
    is one proof of this).
    Moreover General relativity allows all possible frames of reference,
    including those which are accelerated.
    
    Therefore, the question what moves around what is the question
    of choosing a convenient frame of reference. For various purposes
    various frames are convenient. For nautical almanac it is the
    frame where Earth is unmovable. For the long range naval artillery tables
    it is more convenient to assume that the Earth rotates about its (fixed)
    axis.
    For interplanetary mission, Sun-related frame is better. And so on.
    
    A more meaningful poll question would be "what curve describes the Sun
    when it rotates about Earth (or the other way around). It is interesting
    what percentage of people will give the correct answer.
    Unlike the first question, this one has a well defined answer:-)
    
    Alex.
    
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