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Perihelion: The point of the earth's orbit that is nearest to the sun. Although the position is part of a 21,000 year cycle, currently it occurs around January, when the earth is about 3 million miles c . . . View Full Definition

Apsides: The points in the orbit of a planet or moon which are the nearest and farthest from the center of attraction. In the Earth's orbit these are called perihelion and aphelion, and in the Moon's . . . View Full Definition

Anomaly: As applied to astronomy, the anomaly is the angle made at any time by the radius vector of a planet or moon with its line of apsides, the angle being reckoned from perihelion or perigee in t . . . View Full Definition

Anomalistic: Pertaining to the periodic return of the Moon to its perigee or the Earth to its perihelion. The anomalistic month is the average period of the revolution of the Moon around the Earth with r . . . View Full Definition

Elongation: The distance of a planet from the Sun, as viewed from Earth. The maximum elongation for the inferior planets is 28° for Mercury, and 48° for Venus. Mercury can therefore only form a conjunct . . . View Full Definition

Aphelion: The point on the earth's orbit that is farthest from the sun. Although the position is part of a 21,000 year cycle, currently it occurs around July, when the earth is about 3 million miles f . . . View Full Definition