Ever heard of a 鈥penumbral eclipse鈥 of the Moon? What is this? Is it an eclipse? Sort of. Let鈥檚 get to the question 鈥
What is a Penumbral Eclipse?
To be honest, penumbral lunar eclipses are not that exciting if you鈥檙e just looking at the Moon. The Full Moon really doesn鈥檛 change its appearance during a penumbral eclipse as it does during a total eclipse of the Moon.
This is a very subtle kind of eclipse which may appear like a darker-than-usual Moon. Sometimes there鈥檚 a very slight gray shading on one part of the Moon, but almost nobody notices it.
The diagram below shows different types of lunar eclipses. It all depends on the path taken by the Moon as it passes through Earth鈥檚 shadow. If the Moon passes through the outer circle but does not reach the inner circle, it is a penumbral eclipse. .
Still, the penumbral concept is pretty interesting. Turns out, everything casts two different shadows.
- If you look at your own shadow on the sidewalk you鈥檒l see a main part where the Sun is completely blocked out. But there鈥檚 also a less dark blurry fringe surrounding your shadow. That鈥檚 your penumbral shadow. If an ant ventured into this penumbral section it would see the sun partially but not fully blocked.
- Our planet casts a black umbral shadow into space. Anything venturing into it is completely robbed of sunlight. Earth鈥檚 umbral shadow gets smaller and smaller the farther it goes. It tapers like a chopstick and disappears entirely a million miles from us in the anti-sunward direction.
But Earth鈥檚 penumbral shadow behaves differently. It gets larger as it goes farther away from us. So it鈥檚 very easy for a nearby celestial object like the Moon, if its not lined up exactly, to venture into our penumbral but miss our umbral shadow.
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