View at EarthSky Community Photos. | Nils Ribi in Sun Valley, Idaho, caught the November 30, 2020, penumbral lunar eclipse. He wrote: “The penumbral eclipse of the full moon, November 30, 2020, at 2:43 a.m., the time of greatest eclipse, in Sun Valley, Idaho. It was nice to see that the eclipse was not that faint here.” Thank you, Nils!
An eclipse of the moon can only happen at full moon, when the sun, Earth and moon line up in space, with Earth in the middle. So at such times, Earth’s shadow falls on the moon, creating a lunar eclipse. Lunar eclipses happen a minimum of two times to a maximum of five times a year. As a matter of fact, there are three kinds of lunar eclipses: total, partial and penumbral.
In a lunar eclipse, Earth’s shadow falls on the moon. And if the moon passes through the dark central shadow of Earth – the umbra – a partial or total lunar eclipse takes place. Then, if the moon only passes through the outer part of the shadow – the penumbra – a subtle penumbral eclipse occurs. Diagram via Fred Espenak/ Lunar Eclipses for Beginners. Used with permission.
In a total eclipse of the moon, the inner part of Earth’s shadow, called the umbra, falls on the moon’s face. Then at mid-eclipse, the entire moon is in shadow, which may appear blood red.
Next, there is a partial lunar eclipse, where the umbra takes a bite out of only a fraction of the moon. The dark bite grows larger, and then recedes, never reaching the total phase.
Finally, there’s a penumbral lunar eclipse, when only the more diffuse outer shadow of Earth – the penumbra – falls on the moon’s face. In fact, this third kind of lunar eclipse is much more subtle, and much more difficult to observe, than either a total or partial eclipse of the moon. That’s because there is never a dark bite taken out of the moon, as in a partial eclipse. So the eclipse never progresses to reach the dramatic minutes of totality. And at best, at mid-eclipse, very observant people will notice a dark shading on the moon’s face. Others will look and notice nothing at all.
According to eclipse expert Fred Espenak, about 35% of all eclipses are penumbral. Another 30% are partial eclipses, where it appears as if a dark bite has been taken out of the moon. And the final 35% go all the way to becoming total eclipses of the moon, a beautiful natural event.
What to expect from a penumbral eclipse
View larger. | Left, an ordinary full moon with no eclipse. Right, full moon in penumbral eclipse on November 20, 2002. Master eclipse photographer Fred Espenak took this photo when the moon was 88.9% immersed in Earth’s penumbral shadow. There’s no dark bite taken out of the moon. A penumbral eclipse creates only a dark shading on the moon’s face. Image via Fred Espenak. Used with permission.
Some eclipse photos
This is what a total eclipse looks like. This is the total eclipse of October 27, 2004. Image via Fred Espenak.View at EarthSky Community Photos. | Lorraine Boyd in Delmar, New York, wrote: “Even though we had cloudy skies, there were breaks and I was able to capture the full Beaver Moon partial lunar eclipse. It was a beautiful sight to see.” It was, wasn’t it? Thank you, Lorraine!View at EarthSky Community Photos. | Here is the penumbral eclipse of July 4-5, 2020. As you can see, it’s not very noticeable. Greg Redfern in central Virginia commented: “Taken at maximum eclipse for the penumbral lunar eclipse. May be some shading in the upper left quadrant.” Thank you, Greg.
Bottom line: There are three kinds of lunar eclipses: total, partial and penumbral. A penumbral eclipse is very subtle. At no time does a dark bite appear to be taken out of the moon. Instead, at mid-eclipse, observant people will notice a shading on the moon’s face.
Our Editor-in-Chief Deborah Byrd works to keep all the astronomy balls in the air between EarthSky's website, YouTube page and social media platforms. She's the primary editor of our popular daily newsletter and a frequent host of EarthSky livestreams. Deborah created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.
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