parallactic inequality

parallactic inequality

A minor periodic term in the Moon's motion that results from the gravitational attraction of the Sun and causes the Moon to be ahead at first quarter and to lag behind at last quarter (see phases, lunar). The inequality can be used to calculate solar parallax. See also evection; variation.

parallactic inequality

[¦par·ə¦lak·tik ‚in·i′kwäl·əd·ē]
(astronomy)