You can see an example of a very detailed simulation of just the umbra moving across the Earth's surface in the NASA Goddard video Tracing the 2017 Solar Eclipse The precise 3D shape of the Moon generates the shadow and it then moves over the contour of the Earth's topography. Source: Geometry of a Total Solar Eclipse Typically, the umbra is 100–160 km wide, while the penumbral diameter is in excess of 6400 km. Sometimes the Moon is so far away that it can't fill the Sun and there is no umbra at all, that's called an annular eclipse. The umbra has a well defined diameter but the size varies a lot due to variation in the distance from the Moon to the Earth since it's orbit is not circular.
#Umbra eclipse how to#
answer does a good job of explaining how to calculate the diameter of the umbra, and that math could probably be extended to calculate the diameter of the penumbra as well. †Actually this is only true by coincidence because the angular diameter of the Sun happens to be the same as that of the Moon. It's hard to pin down the size of the penumbra because it's fuzzy and fades near the edges, but if you could see the very edges then it would be twice † the diameter of the moon or very roughly 6900 kilometers total. It's a little distorted because it's not directly under the ISS but far off near the terminator. That's a photo of the umbra and penumbra on the surface of the Earth taken from Space. But how big is this shadow? How many kilometers is its diameter?
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