Tidal Acceleration, Fluctuations, and the Earth’s Variable Rotation, to 1939
The proposition that the Moon’s motion was slowly accelerating over the centuries was first put forward by Edmond Halley in 1692.219 Determinations of the size of this acceleration during the 18th and early 19th centuries put it at about 10˝ of increase per century. This meant that the Moon’s mean motion contained the term 10˝T 2, where T represents 100 Julian years of 36525 days each; the increment is equal numerically to half the angular acceleration. The 18th-century astronomers referred to the increment as the “secular acceleration” of the Moon, and this usage continued into the 20th century.
KeywordsLunar Occultation Tidal Friction Secular Acceleration Apparent Acceleration Astronomical Journal
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