February 9: Nevil Maskelyne

Dr Nevil Maskelyne

October 6, 1732 – February 9, 1811

The Reverend Dr Nevil Maskelyne was the fifth English Astronomer Royal. He held the office from 1765 to 1811.

In 1758 Maskelyne was admitted to the Royal Society, which in 1761 despatched him to the island of St. Helena to observe the transit of Venus. This was an important observation since accurate measurements would allow the accurate calculation of Earth's distance from the Sun, which would in turn allow the scale of the solar system to be calculated.

Bad weather prevented any useful observations, however Maskelyne used his journey to develop a method of determining longitude using the position of the moon, the lunar distance method. He returned to England, resuming his position as curate at Chipping Barnet in 1761, and began work on a book, publishing the lunar distance method of longitude calculation in 1763 in The British Mariner's Guide, which included the suggestion that to facilitate the finding of longitude at sea, lunar distances should be calculated beforehand for each year and published in a form accessible to navigators. This proposal, the germ of the Nautical Almanac, was approved by the government, and under the care of Maskelyne the Nautical Almanac for 1767 was published in 1766. He further induced the government to print his observations annually.

The lunar distance method was the predominant method used well into the 19th century. Since Maskelyne's observations and calculations were made at the Royal Greenwich Observatory, the Greenwich meridian eventually became a common base for longitude worldwide and was adopted internationally as the Prime Meridian in 1884.

Maskelyne’s first contribution to astronomical literature was A Proposal for Discovering the Annual Parallax of Sirius, published in 1760. Subsequent contributions to the Transactions contained his observations of the transits of Venus (1761 and 1769), on the tides at Saint Helena (1762), and on various astronomical phenomena at Saint Helena (1764) and at Barbados (1764).

Maskelyne also introduced several practical improvements, such as the measurement of time to tenths of a second; and prevailed upon the government to replace Bird’s mural quadrant by a repeating circle 6 feet (1.8 m) in diameter. The new instrument was constructed by Edward Troughton but Maskelyne did not live to see it completed.

In 1775 he was awarded the Royal Society's Copley medal. The Lunar crater Maskelyne is named in his honor.