James Bradley ( born March 3 1693 Sherborne; † July 13, 1762 in Chalford ) was an English clergyman and astronomer. He pioneered the precise astrometry and discovered the annual aberration of the stars.
Life and work
James Bradley was born in Sherborne at Cheltenham in the County of Gloucestershire. From 1711 to 1718 he studied theology at Balliol College, Oxford. 1719 Bradley Vicar of Bridstow and his friend, the parliamentarians Samuel Molyneux, gave him a prebend in Wales.
Interest in astronomy
In addition to the theology Bradley was very interested in astronomy. First observations he led under the guidance of his uncle, the experienced amateur astronomer Reverend James Pound (1669-1724), the parish Wanstead By in Essex. In 1718 he was admitted as a "Fellow" in the Royal Society.
1721 Bradley was appointed to the University of Oxford, where he took over the Savilian Chair of Astronomy. He held, inter alia, Lectures on " experimental philosophy ".
Bradley's specialty was the astrometry, the positioning of the stars. In his observations of the heavens with a specially constructed zenith telescope, which he undertook with his friend Samuel Molyneux on the Observatory, he discovered in 1725 at the star Gamma Draconis, the phenomenon of the aberration of light caused by the motion of the earth around the sun. This was a first proof of Copernicus ' heliocentric world view and also a way of determining the speed of light. This could Bradley - in contrast to Huygens - determined with an accuracy of one percent. He discussed his findings in 1728 with the court astronomer Edmond Halley and published it in January 1729th
Through precise measurements of the lunar orbit over 19 years, Bradley discovered the nutation of the Earth's axis. The results of his observations he published in 1748.
In 1742 he was appointed as successor by Edmond Halley for " Astronomer Royal" and director of the Royal Greenwich Observatory. Under his leadership, the instruments of the Greenwich Observatory was increased for the time immense sum of £ 1,000. 1750 a quadrant of John Bird was put into operation. 1752 Bradley received an annual salary of £ 250 from the British royal family.
1761, he was forced to resign for health reasons from his offices. He moved to Chalford in Gloucestershire, where at the age of 69 years he died the following year at Skiveralls House.
Publishing and relevance of its research results
The publication of Bradley's star observations were delayed because of a dispute over the copyright. They were eventually published in two volumes in 1798 and 1805. Friedrich Wilhelm Bessel reduced Bradley's records and created a star catalog with 3,000 stars.
James Bradley is seen as one of the founders of the astrometry and thus as one of the greatest astronomers of the 18th century.
Writings (selection )
- A Letter from the Reverend Mr. James Bradley Savilian Professor of Astronomy at Oxford, and FRS to Dr.Edmond Halley astronomer. Reg & c. Giving an Account of a New Discovered Motion of the Fix'd Stars. In: Philosophical Transactions. Volume 35, number 406, 1727, pp. 637-661, doi: 10.1098/rstl.1727.0064, ( full text )
- Hornsby / Robertson ( eds.): Astronomical observations made at the observatory at Greenwich from 1750 to 1762. 2 volumes, Oxford from 1798 to 1805. Supplement 1833.