Question

Eclipse seasons do not occur exactly twice a year. Instead, they occur slightly more often, coming about 173 days apart (which is a bit less than the roughly 182 to 183 days that make up 6 months). Why do they do this, rather than occurring exactly twice each year?

Answer 1

Because the line of nodes travels slowly around the moon's orbit.

Step-by-step explanation:

The trajectory is assumed to become the ecliptic for the Moon's orbit around Earth, not the equatorial plane.

The Sun upon the Moon's gravitational force triggers their nodes to undergo precession slowly westward, performing a cycle in about 18.6 years.