"Earth looked so tiny from the heavens that there were times during the Apollo 8 mission when I had trouble finding it. If you can imagine youself in a darkened room with only one clearly visible object, a small blue-green sphere about the size of a Christmas tree ornament, then you can begin to grasp what Earth looks like from space. I think that all of us subconsciously think that Earth is flat or at least almost infinite. Let me assure you that, rather than a massive giant, it should be thought of as the fragile Christmas tree ball which we should handle with considerable care."

The Island Earth, edited by Oran W. Nicks, NASA (1970)