Charles Mason

Charles Mason
Born	April 1728 (baptised 1 May) Oakridge Lynch, Gloucestershire, England
Died	25 October 1786(1786-10-25) (aged 58) Philadelphia, Commonwealth of Pennsylvania, United States
Nationality	Kingdom of Great Britain
Fields	Astronomy, surveying
Known for	Mason–Dixon line

Charles Mason (April 1728 [baptised 1 May] – 25 October 1786) was an English astronomer who made significant contributions to 18th-century science and American history, particularly through his involvement with the survey of the Mason–Dixon line, which came to mark the border between Maryland and Pennsylvania (1764–1768). The border between Delaware and Maryland is also defined by a part of the Mason–Dixon line.

Mason's early career was spent at the Royal Greenwich Observatory near London. He served as assistant astronomer from 1756 to 1760 under the Reverend James Bradley, the Astronomer Royal.

While employed at the Greenwich Observatory, Mason became familiar with Professor Tobias Mayer’s Tables of the Moon. The Lunar Tables were designed to solve the problem of determining longitude at sea, a challenge that frustrated scientists and navigators for decades. Mason worked throughout his life to perfect the Lunar Tables as a method of improving navigation at sea. In 1787, Mason was awarded £750 by the Board of Longitude for his work on perfecting the Tables.

In 1761, Mason was assigned to travel to the island of Sumatra to observe the transit of Venus as part of an international effort to record data that would enable scientists to determine the distance from the earth to the sun. Mason was joined by Jeremiah Dixon, a surveyor and amateur astronomer from Cockfield in the County of Durham. Owing to an attack by a French man-of-war, they did not reach their destination in time for the transit and were forced to record their observations from the Cape of Good Hope. On the way back from the Cape they visited St Helena where they made a series of observations with the astronomer Nevil Maskelyne.

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