English astronomer who 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 Scotland.

Maskelyne, the fifth Astronomer Royal 1765-1811, began publication 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 studied at Cambridge. He was ordained a cleric but began working at the Greenwich Observatory in London. His first big project in observational astronomy was an expedition to St Helena, under the auspices of the Royal Society, in order to study the solar parallax during the 1761 transit of Venus. At the appropriate moment, however, the weather turned bad and, in any case, he had lost confidence in the instruments he had brought with him. It was not until 1772 that Maskelyne perfected his technique for observing transits, by which time the 1769 transit of Venus had already occurred (and the next would not take place in his lifetime).