Maskelyne, Nevil (1732–1811)

English astronomer. He made observations to investigate the reliability of the lunar distance method for determining longitude at sea. In 1774 he estimated the mass of the Earth by noting the deflection of a plumb line near Mount Schiehallion in Perthshire, Scotland.

Maskelyne was appointed Astronomer Royal in 1765 and held that office until his death. He began publication in 1766 of the Nautical Almanac. This contained astronomical tables and navigational aids, and was probably his most enduring contribution to astronomy.

Maskelyne was born in London and educated at Westminster School and Cambridge. He was ordained a cleric in Barnet in 1755, but began working at the Greenwich Observatory in London, computing tables for James Bradley, at that time Astronomer Royal. Bradley arranged for him to go to St Helena under the auspices of the Royal Society to observe the transit of Venus of 1761. However, he had lost confidence in the instruments he had brought with him, and at the appropriate moment, the weather turned bad. On the voyage, Maskelyne tried out the method of lunars for finding the longitude, and he published it in 1763 in the British Mariner's Guide, the forerunner of all nautical almanacs. It was not until 1772 that Maskelyne perfected his technique for observing transits, by which time the 1769 transit of Venus had also passed. The next would not take place in his lifetime.