Lunar theory

Japanese: 月運動論 - つきうんどうろん（英語表記）lunar theory

This is a branch of celestial mechanics that deals with the motion of the Moon as it revolves around the Earth. The Moon's motion is extremely complex due to the large perturbation force of the Sun, and because the Moon is close to the Earth, highly accurate observations have been made since ancient times. Thus, the content of the theory of lunar motion, which elucidates complex motion with high precision, is extremely vast. In the representative lunar theory of motion by E. W. Brown, the trigonometric series representing the Moon's ecliptic longitude, ecliptic latitude, and parallax consists of a total of more than 1,600 periodic terms. More than half of these are used for the ecliptic longitude, and the five most important periodic terms among them are called the central difference, the deviation, the mean of second difference, the annual difference, and the lunar angular difference.

Source: Heibonsha World Encyclopedia, 2nd Edition Information

Japanese:

地球の回りを公転する月の運動を論ずる天体力学の一分科である。月の運動は太陽の摂動力が大きいためにたいへん複雑であり，そのうえ月は地球に近いので高い精度の観測が昔から行われてきた。こうして，複雑な運動を高い精度で解明する月運動論の内容はきわめて膨大なもので，代表的なE.W.ブラウンの月運動論では，月の黄経，黄緯，視差を表す三角級数は全体で1600余の周期項からなっている。その半数以上が黄経に使われているが，その中でもっとも主要な5個の周期項は中心差，出差，二均差，年差，月角差と呼ばれている。

出典　株式会社平凡社世界大百科事典第２版について　情報

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