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How much smaller does the sun appear because of its gravity ?

  1. May 4, 2015 #1
    How much smaller does the sun appear because of it's gravitational field ?

    415px-Cassini-science-br.jpg

    This illustration shows EM waves being bent by the gravitational well of the sun.

    The light from the sun itself will also be bent by its gravitational well, making the sun appear smaller , ( and have barrel distortion ).

    So how much smaller does the sun's disc appear, compared with it's true diameter ?.

    [ Next question: what will be the shrinkage with giant stars whose mass is 1000x suns ? ].
     
  2. jcsd
  3. May 4, 2015 #2

    A.T.

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    Why smaller?
     
  4. May 4, 2015 #3
    I thought the rays from the perimeter of the sun would be bent by gravity toward the observer-sun axis , making the sun look smaller when viewed from Earth* , [ * not an atmospheric effect , for the purposes of this question assume Earth has no atmosphere ].
     
  5. May 4, 2015 #4

    A.T.

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    Why would that make the Sun look smaller?
     
  6. May 4, 2015 #5
    by your repetition are you subtly hinting that I've got the wrong end of the stick and the sun appears larger because of gravitational lensing ?.
     
  7. May 4, 2015 #6
    Hmm, it just occurred to me that the edges of the far hemisphere of the sun would become visible from Earth because of the gravitational distortion : that would make the sun appear bigger.
     
    Last edited: May 4, 2015
  8. May 4, 2015 #7

    A.T.

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    The visual size depends on the angle at which the most outer rays arrive at the eye, not on which parts of the object send these rays. In general these two things are independent, but in this case they happen to coincide: you see the sun bigger and more parts of it.
     
  9. May 4, 2015 #8
    What would be the effect on something really massive like a galaxy ? :
    would it just appear uniformly magnified ?, or with radial distortion, ( see attached) ...

    how different is real shape of galaxy from how it appears.jpg
     
    Last edited: May 4, 2015
  10. May 4, 2015 #9

    A.T.

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  11. May 7, 2015 #10
    Light coming out of the Sun is moving [em]radially[/em] with respect to the Sun, so it won't be bent, only "slowed" so to say. To be bent its direction vector has to have tangential component.

    Edit: by "slowed" I mean gravitational redshift, of course.
     
  12. May 7, 2015 #11

    phyzguy

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    This is incorrect. Draw yourself a picture of a ray coming from the edge of the sun to an observer on Earth. It is certainly not moving radially.
     
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