When the Earth casts a shadow on the moon, what shape is it?

Answer 1

Hi Armando R.,

An intriguing question. Not because of the essential optics involved (after all, since the Earth is approximately circular, and the Sun may be considered a point source, the shadow traced back to the Earth is approximately a circular arc to the eye.

But, what shape does that shadow edge actually have on the Moon's curved surface? That is obviously a much more involved question, since it is a 3-dimensional curve ....