Viewing a single comment thread. View all comments

nmxt t1_itpy6if wrote

All celestial events occur in cycles, so whenever a cycle is complete, the same events occur again. In case of solar eclipses, the cycle is about 18 years (called a “saros”). This is a period of time in which the Moon and the Sun both complete whole numbers of their own cycles, setting them to repeat the same events all over again.

8

Comprehensive-Ad3963 t1_itq1iju wrote

The moon completes an orbit every 27 days.
The Earth completes an orbit around the Sun every 365.2422 days (it may help to pretend the Sun orbits the Earth)

A solar eclipse happens when a line from the Earth to the Sun intersects with the Moon.

We can figure out when that happens using some circle geometry (we can get better predictions using ellipses):

Pull out a piece of paper and draw two circles, one inside the other and each having the same center. The outer one represents the Sun's fictional orbit around the Earth, and the inner one represents the Moon's actual orbit around the Earth. Draw 3 dots, one at the center of the circles, such that the three dots form a line. The outermost dot is the Sun, the next outermost the Moon, and the innermost the Earth. This is a total solar eclipse.

The Sun "moves" 2*pi radians over the course of 365.2422 days, while the Earth moves that many radians over the course of 27 days.

2