annual equation(annual inequality) The periodic inequality in the Moon's motion that arises from variations in solar attraction due to the eccentricity of the Earth's orbit. Its period is the anomalistic year and the maximum displacement in longitude is 11′8″.9. See also evection; parallactic inequality; variation.
annual equation[′an·yə·wəl i′kwā·zhən]
A variation in the moon's apparent motion caused by variations in the distance of the earth from the sun during the course of the year.