# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Astro*Dictionary by Michael Erlewine





1 article for "Evection"

Evection [Astro*Index]

The largest inequality in the equation for the Moon's longitude. It is due to the disturbing gravitational force of the Sun. This force produces periodic changes in the eccentricity of the Moon's orbit, depending on the position of the line of apsides with regard to the Sun in successive lunations. When the Moon is furthest from the Earth, at apogee, this force is strongest; it is weakest when the Moon is at perigee, or nearest to the Earth. This was discovered by Hipparchus.

See also:
♦ Eccentricity ♦ Line of Apsides ♦ Apogee ♦ Perigee


Astro*Index Copyright © 1997 Michael Erlewine