English: Blue line: Earths orbit
Grey line: Moon orbit
Green line: Line of nodes
Yellow line: Line to perigee
Red lines: Velocity vectors
Middle:
(Camera follows Earth keeping Sun always behind it.)
Demonstrates how the inclination of the moon's orbit precludes eclipses most of the time, leading to distinct eclipse seasons.
Bottom left:
(Camera follows Earth keeping its initial orientation, "Sun passes Earth" once per year .)
Shows that the periodicity and recurrence of eclipses is governed by the Saros cycle, a period of approximately 6,585.3 days (18 years 11 days 8 hours). It was known to the Chaldeans as a period when lunar eclipses seem to repeat themselves, but the cycle is applicable to solar eclipses as well.
Bottom right:
View from the top shows how the moon orbital elements (argument of perigee PE and longitude of ascending node AN) change with time, returning to a similar configuration after one saros.
One saros period after an eclipse, the Sun, Earth, and Moon return to approximately the same relative geometry, a near straight line, and a nearly identical eclipse will occur, in what is referred to as an eclipse cycle.