James Bradley (September 1692 – 13 July 1762) was an English astronomer and priest who served as the third Astronomer Royal from 1742. He is best known for two fundamental discoveries in astronomy, the aberration of light (1725–1728), and the nutation of the Earth's axis (1728–1748).

These two discoveries were called "the most brilliant and useful of the century" by Jean Baptiste Joseph Delambre, historian of astronomy, mathematical astronomer and director of the Paris Observatory. In his History of astronomy in the 18th century (1821), Delambre stated:

He took orders on becoming vicar of Bridstow in Herefordshire in the following year, and a small sinecure living in Wales was also procured for him by his friend Samuel Molyneux. He resigned his ecclesiastical preferments in 1721, when appointed to the Savilian chair of astronomy at Oxford. As reader on experimental philosophy from 1729 to 1760, he delivered 79 courses of lectures at the Ashmolean Museum. was, for all realistic purposes, conclusive evidence for the movement of the Earth, and hence for the correctness of Aristarchus', Copernicus', and Kepler's theories; it was announced to the Royal Society in January 1729.

The theory of the aberration also gave Bradley a means to improve on the accuracy of the previous estimate of the speed of light, which had previously been estimated by the work of Ole Rømer and others.

The publication of Bradley's observations was delayed by disputes about their ownership; but they were finally issued by the Clarendon Press, Oxford, in two folio volumes (1798, 1805). The insight and industry of the German astronomer Friedrich Wilhelm Bessel were, however, needed for the development of their fundamental importance.

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References

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  • Online catalogue of Bradley's working papers (part of the Royal Greenwich Observatory Archives held at Cambridge University Library)