GEORGE BERNARD / SCIENCE PHOTO LIBRARY GEORGE BERNARD / SCIENCE PHOTO LIBRARY
James Bradley (1693-1762), English Astronomer Royal. Bradley is chiefly remembered for his work on stellar parallax and the speed of light. Stellar parallax is the slight shift in the apparent position of stars which is observed when the Earth is at opposite ends of its orbit. Bradley measured this, but discovered it to be larger than could be accounted for by the shift in the Earth alone. The remainder was due to the velocity of the Earth relative to the speed of light; in the frame of reference of a moving Earth, light will necessarily be bent. So observations will be very slightly altered. From this Bradley estimated the speed of light. Taken from an 1849 publication.
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