1. a periodic variation in the moon’s motion caused by the gravitational influence of the sun
Usage: astronomy

Examples

• Evection is one of the largest perturbations in the moon’s orbit.
• Ancient astronomers noticed irregularities in lunar motion that we now call evection.
• The evection cycle has a period of about 31.8 days.
• Ptolemy was the first to describe evection in his astronomical works.
• Modern calculations of lunar position must account for evection.
• The amplitude of evection can reach up to 1.3 degrees in longitude.