On March 2nd of the year 1105, the Moon barely dipped its toe into Earth’s outer shadow, the penumbra. The eclipse was so faint and short that it probably went unnoticed. But it marked the start of a cycle that will last 1300 years and feature 73 eclipses. And the next one takes place tomorrow night. The full Moon – the Harvest Moon – will pass through the penumbra, and barely touch the darker inner shadow, the umbra.

Eclipses occur in cycles known as Saros. This eclipse is part of Saros 118.

The Moon starts a cycle at the far north or south of our planet’s shadow. Over the centuries, it moves through the shadow, until it exits at the opposite pole. So a Saros begins with penumbral eclipses, then moves through partial eclipses, total eclipses, then back again. The next eclipse in this Saros will take place in September of 2042.

This eclipse is number 52 in the series. It’ll begin at 7:41 p.m. Central Time, when the Moon first touches the penumbra. Later, the Moon will barely dip into the umbra, so it’ll look like a celestial dragon took a tiny nibble from the Moon. At least part of the eclipse will be visible from the entire United States except western Alaska.

So look for the almost-full Moon tonight, with the bright planet Saturn close by. Then tomorrow night, see if you can follow the subtle shading of a faint lunar eclipse.

Script by Damond Benningfield