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Penumbral Lunar Eclipse


Last updated 12/11/2020 at 1:20pm

Watch out for the penumbral eclipse this week.

Did you ever wonder what folks During the predawn hours of Nov. 30, night owls and insomniacs in North America may see an eclipse of the moon as our nearest natural satellite drifts through the Earth's shadow as it orbits our planet.

Technically, I should say "shadows" because the Earth (and all solid bodies illuminated by the sun) casts two shadows into space: a dark inner shadow we call the umbra and a light outer shadow known as the penumbra. You'll notice the same phenomenon on a sunny day if you cast the shadow of your hand onto a wall or sheet of white paper about two or three feet away and look carefully at the shadow's edge.

These two shadows of our planet help create several types of lunar eclipses. The first, and most dramatic, is a total eclipse. This occurs when the moon enters completely into the Earth's dark umbral shadow.

The next type is a partial lunar eclipse. We see a partial eclipse when the moon only partially enters the Earth's umbra; this occurs just before and after a total eclipse, but also when the moon only skims partly through the umbra.

Finally, there's what we call a penumbral eclipse when the moon doesn't pass very close to the Earth's umbra but slips only through its light, outer shadow. If you recall, we experienced one of these penumbral lunar eclipses on July 4 of this year – it was nearly impossible to see with the unaided eye – and this is the type that will occur again on Nov. 30.

This one, however, may be easier to detect since the moon will pass deeper into the penumbra, and closer to the umbra, than it did in July, and its northern edge will appear to darken slightly more. You still must pay close attention, or you may miss it altogether.

The eclipse begins at 11:32 p.m. PST on Nov. 29 (2:32 a.m. EST on Nov. 30) and ends at 3:53 a.m. PST (6:53 a.m. EST) on Nov. 30.

The maximum eclipse, and our best chance of noticing any darkening at all, occurs only when the moon enters deepest into the penumbral shadow from around 1:40 to 1:50 a.m. PST (4:40 to 4:50 a.m. EST).

Keep in mind that you'll be looking only at a full moon, so you will not need a filter to protect your vision. You may, however, want to aim binoculars in the moon's direction for a closer view.

If you miss this eclipse – and many of us may because it will be quite subtle – we all should have better luck in 2021. Before sunrise on May 26, 2021, the eastern part of North America will experience a partial lunar eclipse, while those in the western part will see a total eclipse. In November of next year, however, all of North America will be treated to a very deep partial eclipse that will appear nearly total. Both will create impressive sky shows to watch.

In the meantime, set your alarm so you don't miss the penumbral eclipse next Monday morning. And even if it's too subtle to see, at least you'll get to enjoy a beautiful full moon descending in the west!

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