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Stellar abberation (water in telescope)

  1. Feb 18, 2016 #1


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    I've been reading about stellar aberration and was particularly drawn to the experiment where two telescopes are tracking a star but one is filled with water to slow the speed of light down. The results of the experiment show both telescopes to be tilted to exactly the same angle which contradicts logic. This is explained somewhat in wiki as a byproduct of length contraction. I don't understand how length contraction can fix this. Can someone help out? Thanks.
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  3. Feb 18, 2016 #2


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    have you got some references for that please ?

    never heard of a telescope filled with water
  4. Feb 18, 2016 #3


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    From Wikipedia "Stellar Aberration"

    "However, it soon became clear Young's theory could not account for aberration when materials with a non-vacuum index of refraction were present. An important example is of a telescope filled with water. The velocity of the light in such a telescope will be slower than in vacuum, and is given by dc93a0c5ed672fbf1037df2d65a34952.png rather than 4a8a08f09d37b73795649038408b5f33.png where 7b8b965ad4bca0e41ab51de7b31363a1.png is the index of refraction of the water. Thus, by Bradley and Young's reasoning the aberration angle is given by

    [PLAIN]https://upload.wikimedia.org/math/4/5/3/453fb5ca1793c35cb0666e886fad9665.png. [Broken]
    which predicts a medium-dependent angle of aberration. When refraction at the telescope's objective is taken into account this result deviates even more from the vacuum result. In 1810 Fran├žois Arago performed a similar experiment and found that the aberration was unaffected by the medium in the telescope, providing solid evidence against Young's theory. This experiment was subsequently verified by many others in the following decades, most accurately by Airy in 1871, with the same result.[14]"
    Last edited by a moderator: May 7, 2017
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