An Etymological Dictionary of Astronomy and Astrophysics

1. General: An instance of changing, or something that changes.
   

2. Astro.: The periodic inequality in the Moon’s motion that results from the combined gravitational attraction of the Earth and the Sun. Its period is half the synodic month, that is 14.77 days, and the maximum longitude displacement is 39'29’’.9.
   

See also:

→ calculus of variations, → annual variation, → secular variation.

Etymology (EN): M.E., from O.Fr. variation, from L. variationem (nominative variatio) “difference, change,” from variatus, p.p. of variare “to change,” → vary.

Etymology (PE): Varteš, verbal noun from vartidan, → vary.