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Thread: Questions in astrophysics.

  1. #1 Questions in astrophysics. 
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    Imagine that you are surveying the sky, and take images of two galaxies. Galaxy A looks twice as wide as Galaxy B - i.e. it subtends twice the angle as viewed from the Earth, with an apparent radius of twice as many pixels.
    Which one of these statements cannot be true?

    If the two galaxies are really the same size, B must be twice as far away as A.

    If the two galaxies are at the same distance from the Earth, B must be half the size of A

    If galaxy B is really twice as large as A, it must be four times further away.

    If galaxy A is really four times as big as galaxy B, it must be twice as far away.

    If galaxy B is really half the size of galaxy A, it must be twice as far away.
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  2. #2  
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    Okay, so I know the answer. What is it that you cannot figure out?
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  3. #3  
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    Quote Originally Posted by pikpobedy View Post
    Okay, so I know the answer. What is it that you cannot figure out?

    I already know the answer too. It was a practice question from a course I am taking. So, what is the answer you know?
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  4. #4  
    KJW
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    Quote Originally Posted by mayflow View Post
    I already know the answer too. It was a practice question from a course I am taking. So, what is the answer you know?

    MODERATOR NOTE: It doesn't work that way when it comes to asking homework questions. You need to give the answer first.
    A tensor equation that is valid in any coordinate system is valid in every coordinate system.
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  5. #5  
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    Well, takes a bit of the fun out of it, but the answer is that the answer that cannot be true is If galaxy B is really half the size of galaxy A, it must be twice as far away.

    AND, I already said it was just a practice question that I already know the answer to.
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