05/21/2021 – Ephemeris – For everything there is a season… even eclipses

This is Ephemeris for Friday, May 21st. Today the Sun will be up for 15 hours and 3 minutes, setting at 9:11, and it will rise tomorrow at 6:07. The Moon, 2 days past first quarter, will set at 4:14 tomorrow morning.

There are seasons for everything: baseball season, football season, spring, summer, what have you. There are also eclipse seasons. The Moon’s orbit is tilted by about 5 degrees to the ecliptic, the path of the Sun in the sky. The points where they cross are called nodes, 180 degrees apart. When the Sun is near one of those nodes we are in an eclipse season, where a solar eclipse can occur at new moon, and a lunar eclipse can occur at full moon. We are guaranteed one of each per eclipse season, and on rare occasions a third eclipse. Of course one has to be at the right place to see an eclipse. This eclipse season we will be at a marginal place to see both eclipses. Both are at sunrise, so we’ll see just a part of each of them.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan. They may be different for your location.

Addendum

A diagram of the paths of the Moon and Sun projected on the sky (celestial sphere). N1 and N2 are the nodes (crossing points). Nodes are ascending or descending depending on the northerly or southerly component of the Moon’s motion in crossing them. The Sun and Moon move in an easterly direction, but the Moon’s orbit precesses so that the line of nodes move in a westerly direction once around in 18.6 years. That’s why eclipse season intervals are 173.3 days and move backward in the calendar one year to the next. Eclipse seasons occur when the Sun is less than about 17.5 degrees from a node. Credit Earthsky.org.

For a more extensive treatment of this subject check out: https://earthsky.org/astronomy-essentials/definition-what-is-an-eclipse-season