Nevil Maskelyne

Nevil Maskelyne (1732–1811) was an English astronomer who served as Astronomer Royal from 1765 until his death. He advanced astronomical navigation and oversaw the publication of the Nautical Almanac.

Nautical Almanac: An annual publication of astronomical tables and data used to determine positions at sea and on land. Maskelyne established its publication to make lunar-distance navigation more practical.
Transit of Venus: An astronomical event in which Venus passes across the face of the Sun as seen from Earth. Maskelyne observed the 1761 transit during an expedition to Saint Helena.
James Bradley: An English astronomer who served as Astronomer Royal before Maskelyne and discovered stellar aberration and nutation. Bradley's observations formed part of the Greenwich legacy Maskelyne inherited.
Astronomer Royal: The official title of the director of the Royal Observatory, Greenwich, and a senior British astronomical post. Maskelyne's long tenure made the office central to national navigation and astronomy.
Lunar distance method: A method of finding longitude by measuring the angular distance between the Moon and another celestial body. Maskelyne championed this method as a navigational alternative to marine timekeepers.
Saint Helena: A volcanic island in the South Atlantic Ocean, historically used as a site for astronomical observations. Maskelyne travelled there to observe the Transit of Venus and test navigation methods.
Charles Mason: An English astronomer and surveyor who worked on the Mason–Dixon boundary survey. Mason collaborated with Maskelyne on the 1761 Transit of Venus expedition.
Longitude Act: The British statute of 1714 that offered rewards for reliable methods of determining longitude at sea. The act created the policy framework in which Maskelyne evaluated longitude methods.
Longitude: A geographic coordinate measuring position east or west of a reference meridian. Solving longitude at sea was the practical problem that shaped Maskelyne's work.
Schiehallion experiment: An 18th-century experiment that inferred Earth's density from the gravitational deflection of a plumb line near a mountain. Maskelyne led the observations that turned the mountain's mass into a measurement of Earth's density.

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