[jeffwass]

That dark edge is an artefact of the delay in capturing the three monochrome pictures through the different RGB filters.

The article says : "Combining three images taken about 30 seconds apart as the moon moves produces a slight but noticeable camera artifact on the right side of the moon. Because the moon has moved in relation to the Earth between the time the first (red) and last (green) exposures were made, a thin green offset appears on the right side of the moon when the three exposures are combined. This natural lunar movement also produces a slight red and blue offset on the left side of the moon in these unaltered images."

[mark-r]

It also says "A thin sliver of shadowed area of moon is visible on its right side." which is a better explanation. It's not a shadow on the Earth, it's the dark part of the moon.