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Thread: How did Bradley determine the speed of light in 1779?

  1. #1 How did Bradley determine the speed of light in 1779? 
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    How did Bradley determine the speed of light?


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    In 1728 James Bradley made another estimate by observing stellar aberration, being the apparent displacement of stars due to the motion of the Earth around the Sun. He observed a star in Draco and found that its apparent position changed throughout the year. All stellar positions are affected equally in this way. (This distinguishes stellar aberration from parallax, which is greater for nearby stars than it is for distant stars.) To understand aberration, a useful analogy is to imagine the effect of your motion on the angle at which rain falls past you, as you run through it. If you stand still in the rain when there is no wind, it falls vertically on your head. If you run through the rain, it comes at you at an angle, and hits you on the front. Bradley measured this angle for starlight, and knowing the speed of the Earth around the Sun, he found a value for the speed of light of 301,000 km/s.
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    Thanks Alex, but I was hoping for a bit more detail than I already got from reading Wikipedia.
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    There's quite a bit of detail here, including the formulas used to calculate it:
    Aberration of light - Wikipedia, the free encyclopedia
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    Quote Originally Posted by Harold14370 View Post
    There's quite a bit of detail here, including the formulas used to calculate it:
    Aberration of light - Wikipedia, the free encyclopedia
    He was working at the limits of his instruments, if not beyond them.
    How was he able to eliminate all the other motions that would have interfered with his calculations?
    How was he able to correct measurement errors?
    Was he using some form of statistical analysis to correct his observations?
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