Sorry, I'm a newbie here and didn't know how to start a new thread, so I posted a question in another forum and then figured out how. I'm trying to redirect answers here. I'm arguing with a friend about how a half-Earth would appear from the Moon. Since we see the Moon in phases, it makes sense that watching the Earth from the Moon would also offer the same phenomenon, Full Earth, Half Earth, New Earth. My question is if one is looking at a Half Earth from the Moon, would the shadow line appear horizontal or vertical. My belief is that since the Moon is in a roughly equatorial orbit around the Earth, then the equators of the two objects are facing each other, with their axes within a few degrees of being parallel. Since we see the Half Moon as vertical from here, I conclude since there is no mechanism I can envision which would alter the perception, it should appear as a vertical line on the Earth as well. My friend believes the shadow line should appear horizontally across the Earth. I'd welcome any comments or explanations.