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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.
Born 1693 in Sherborne, Gloucestershire; died July 13, 1762, in Chalford, Gloucestershire. English astronomer; member of the London Royal Society (1718). Professor at Oxford University (1721).
Continuing the observations of the amateur astronomer S. Molyneux, which were intended to discover the annual parallax of stars, Bradley noticed a periodical shift of the star γ Draconis that was not accounted for by parallax; this led him to the discovery of the aberration of light (1725). He informed the London Royal Society of this in January 1729. He also discovered the nutation of the earth’s axis (1737), but he announced this discovery only in 1748, after he determined its period. After the death of E. Halley in 1742, Bradley became director of the Greenwich Observatory. In 1750 he began his meridional observations, which yielded material for determining continuous aberration, precession, and nutation; these observations long served to determine the movements of the stars.