In most pictures of a lunar eclipse, the face of the moon you see is a black sphere, as in the image above. With the sun directly on the other side of the moon from us, the side we see is entirely in the shadows, a black hole.
Visualization specialists at NASA decided to fill in that space. Working off an image collected on October 7, 2010, Scott Wiessinger and Ernie Wright matched imagery of the lunar landscape directly onto where it would have appeared had there been any light shining on it. They were extremely precise -- using animation software to get the angles, distances, and features all into their proper places around the sphere. In the end, according to a NASA press release, "The two images were put together and the overlay was exact. The mountains and valleys on the horizon of the LRO [Lunar Reconnaissance Orbiter] picture fit right into the shadows seen by SDO [Solar Dynamics Observatory]."
The resulting image doesn't look quite real -- and of course, by a certain definition, it's not: You could never see this during an eclipse. And yet, that is what's there, and thanks to a little computer software and a lot of careful observation, we can see it.
For a side-by-side comparison:
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