Evection (Latin for “carrying away”), in astronomy, the largest inequality produced by the action of the sun in the monthly revolution of the moon around the earth. The deviation expressed by it has a maximum amount of about 1° 15′ in either direction. It may be considered as arising from a semi-annual variation in the eccentricity of the moon’s orbit and the position of its perigee. It was discovered by Ptolemy.
Evection
