by Bill Arnett
Why does the totally eclipsed Moon (when fully within the umbra) look brighter and whiter on the side nearer the edge of the Earth's shadow? It would seem that it should be uniformly dark as no sunlight is reaching it. At least directly. My hypothesis is that there is some light reaching it from light scattered by the Earth's atmosphere and that this light is brighter and whiter when the Sun from the Moon's perspective is nearer the Earth's limb. It is as if the Earth's shadow has no sharp umbral region but rather a gradually darkening zone. Anyone got a better theory?
Too bad the Moon isn't bigger than the Earth's shadow. Then we could see the whole shadow at once on the face of the Moon. OTOH, that would screw up solar eclipses, not a good tradeoff :-)
I was a little confused by this effect this evening. I didn't see much of the partial phase before totality due to clouds. But I must have been a good boy this month because the sky cleared (mostly anyway) during totality. But the Moon looked very asymmetric: bright and white on one side and orange/pink on the other almost as if it were still not completely in the umbra. Starry Night confirmed that the umbra was indeed covering the whole Moon so I made up the above theory. When the Moon reached the edge of the umbra it was very obviously different from what I was seeing during totality.
It sure is fun the way the Moon looks different in different light. Eclipses are a radical case :-)