Edited by Michelle Ho
On November 19th 2021, we got to experience the longest partial lunar eclipse since 1440 and will remain the longest partial lunar eclipse until 2669. Many upcoming lunar eclipses will have a longer umbral contact, including the upcoming November 2022 lunar eclipse.
Lunar eclipses occur when the moon, Earth and sun all line up. With the Earth in the middle, this means that the Earth’s shadow falls on the moon, which would have otherwise reflected off of the moon’s surface (Earth Sky, 2020).
There are three different types of eclipses: total, partial and penumbral lunar eclipse.
A total lunar eclipse occurs when the inner part of the Earth’s shadow, also known as the umbra, falls on the moon’s surface. At mid-eclipse, the moon is completely in the Earth’s shadow, leading the moon to appear blood red. The moon appears blood red because the sun rays pass through the Earth’s atmosphere, and since the sun rays are composed of a range of frequencies, the green to violet portion of the light spectrum is filtered out while the reddish portion of the spectrum isn’t affected as much. The reddish light also gets refracted when it enters the atmosphere and when it leaves the atmosphere, which leads to the blood-red colour of the moon (Earth Sky, 2019).
A partial lunar eclipse occurs when the umbra only blocks a fraction of the moon while building up to the mid-eclipse. The dark spot on the moon grows larger and larger, but never reaches the stage of a total lunar eclipse.
A penumbral lunar eclipse occurs when only the moon diffuses the outer shadow of the Earth, called the penumbra, falls on the moon’s surface. This type of lunar eclipse isn’t as easy to observe compared to the total and partial lunar eclipses since they don’t have a dark spot that has been taken out of the moon. At best, only observant people can see a dark shading on the moon’s surface (Earth Sky, 2020).
References
Earth sky. (2019, January 18). Why does moon in total eclipse look red? Retrieved
November 23, 2021, from https://earthsky.org/space/why-does-the-moon-look-red-
during-a-total-lunar-eclipse/
Earth sky. (2020, June 29). Retrieved November 23, 2021, from
https://earthsky.org/astronomy-essentials/what-is-a-penumbral-eclipse-of-the-moon/
Lunar eclipse geometry [Photograph]. (2019, January 19). Earth Sky.
https://earthsky.org/astronomy-essentials/what-is-a-penumbral-eclipse-of-the-moon/
Partial eclipse [Photograph]. (2021, November 18). Wikipedia.
https://en.wikipedia.org/wiki/November_2021_lunar_eclipse
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