The first astronomer royal, as the director is still called, was the Rev. John Flamsteed (1646-1720), who received a salary of 100 pounds a year, from which he had to provide Instruments and assistants. Not until James Bradley (1692-1762) used perfected Instruments did work of the observatory become sufficiently precise to remain of value for modern investigations. Bradley became famous for his discovery of the aberration of light and nutation. His successor, the Rev. Nevil Maskelyne (1732-1811), inaugurated the Nautical almanac for the use of seamen. It contained the best available positions of celestial bodies which, in conjunction with the chronometer, developed by this time, furnished an improved method of determining positions at sea. Under sir George B. Airy (1801-92) activity of the observatory in fundamental astronomy was greatly increased. Long series of observations were accumulated on the sun, moon, major planets, and brighter stars, forming the basis for modern astronomical tables.
In 1822 the observatory was placed under control of the Navy, and one of its principal duties became the checking of navy chronometers. This required establishment of a time-service that gradually became a model for all national observatories. In 1880 the time of the Greenwich meridian became legal time throughout the British Isles and, as a result of an international conference at Washington in 1884, this meridian, which passes through the center of Airy's transit instrument, was adopted as the origin of the world longitudes and of the zone time system. Beginning with 1925, all astronomical ephemerides use Greenwich civil time (G.C.T.) under the name of universal time (U.T.).
Since Airy's directorship, Greenwich Observatory has contributed notably to various phases of astrophysics, while continuing its contribution to positional astronomy. Its work, however, was increasingly handicapped by growth of the city around the once isolated location, and a site more suited to its requirements was acquired by the Admiralty. After two and three-quarter centuries the old location was abandoned and the institution removed to Hurstmonceux Castle, some 40 miles southeast of London, four miles from the channel coast of Sussex. This castle, originally built in 1440 and restored to its early splendor in 1935, provides ample room in its 370-acre compound for the observatory and the Nautical Almanac Office, and makes a magnificent home for the oldest scientific institution of Great Britain.
