Bradley, James, 1693–1762, English astronomer. His discovery of the aberration of light, announced in 1728, provided an important line of evidence for the motion of the earth around the sun. In 1742 Bradley became the third Astronomer Royal. Under his direction the observatory at Greenwich was supplied with new instruments; with some of these he cataloged the positions of more than 3,000 stars. His second important discovery, the nutation, or
nodding,of the earth's axis, was only made known in 1748, after it had stood the test of careful observations over a period of nearly 19 years.
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