The full Moon will fade a bit in the wee hours of tomorrow morning. The effect isn’t especially obvious, but it should be noticeable.

The reason is an eclipse. But it’s a penumbral eclipse, which means the Moon will pass through the faint outer ring of Earth’s shadow. None of the Moon will go completely dark, as it does during a partial or total eclipse. Instead, most of the lunar disk will take on a dusky appearance — as though it were covered by a thin layer of clouds.

Eclipses occur in cycles. Each eclipse in a cycle is separated by 18 years and 11 days. The last eclipse in this cycle, for example, took place on November 20th of 2002. And the next one comes on December 11th of 2038.

A cycle begins with a series of penumbral eclipses. The Moon then moves deeper into the shadow of Earth, eventually creating a set of total eclipses. It then moves back out of the shadow, ending with more penumbral events. The current cycle is in that phase, so all the remaining eclipses are penumbral, with the last one in 2291.

Tonight’s eclipse gets underway at 1:32 a.m. Central Time, when the shadow first touches the Moon. It’ll be at its peak at 3:44 a.m., when the penumbra will cover about two-thirds of the lunar disk. The eclipse will end at 5:53, when the Moon exits the penumbra. As a bonus, the Moon has a bright companion all night: Aldebaran, the eye of Taurus, the bull.

Script by Damond Benningfield

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