Flamsteed, John (1646–1719)

English astronomer. He began systematic observations of the positions of the stars, Moon, and planets at the Royal Observatory he founded at Greenwich, London, in 1676. His observations were published in Historia Coelestis Britannica (1725).

As the first Astronomer Royal of England, Flamsteed determined the latitude of Greenwich, the slant of the ecliptic, and the position of the equinox. He also worked out a method of observing the absolute right ascension (a coordinate of the position of a heavenly body) that removed all errors of parallax, refraction, and latitude. Having obtained the positions of 40 reference stars, he then computed positions for the rest of the 3,000 stars in his catalogue.

Flamsteed was born at Denby, near Derby and studied at Cambridge. He began his astronomical studies at home by observing a solar eclipse in 1662. In 1672, he determined the solar parallax from observations of Mars. He early acquired a reputation as an accomplished astronomer, and was appointed astronomer to Charles II in 1675. When Charles II was informed that it was possible to determine longitude at sea by observing the position of the Moon, Charles asked his advisers for a full report. Among these advisers was Jonas Moore (1617–1679), the surveyor general of the ordnance, who consulted Flamsteed. When Flamsteed pointed out that neither the motion of the Moon nor the positions of the stars was sufficiently well known for this purpose, Charles appointed him ‘our astronomical observator, forthwith to apply himself with the most exact care and diligence to the rectifying the tables of the motions of the heavens, and the places of the fixed stars, so as to find out the so-much-desired longitude of places for the perfecting of the art of navigation’. Flamsteed himself laid the foundation stone of the observatory designed by Christopher Wren on 10 August 1675. Flamsteed House, as this building is called, was completed in July 1676 and is now preserved as part of the National Maritime Museum.

At first Flamsteed was harassed by lack of funds. He was given nothing for instruments or for skilled help. To pay for these he took pupils in mathematics and astronomy, and as a result regarded his astronomical observations as his private property. This led to trouble with the Royal Society, and with Sir Isaac Newton in particular, which embittered Flamsteed's later years. His lunar calculations were urgently needed by Newton and by Edmond Halley to test their theories, but Flamsteed withheld them and fell out with both in 1704.

Flamsteed's achievements were the construction of a catalogue of the stars more extensive and more precise than any other existing, and the systematic observation of the Sun, Moon, and planets with a view to revising the theories of their apparent motions and constructing tables from which their positions could be accurately computed. He introduced new methods into practical astronomy, many of them still in use today. In accuracy his observations far exceeded those of his contemporaries; they were, in fact, the earliest observations from which the phenomenon of aberration was clearly deducible.

His work was completed by Crosthwait and Sharp, who had been his private assistants. The three volumes of his Historia Coelestis Britannica contain a record of all his astronomical observations and also the British Catalogue of nearly 3,000 stars. The associated Atlas Coelestis was published in 1729.