Here’s Jim Lovell recalling the Apollo 8 mission:
The big surprise is the Earth—it’s not a surprise that we thought we’re going to see something else—but just suddenly looking at it and seeing it as a small body that you can completely hide behind your thumb. You’re only 240,000 miles away, but everything that you have ever known is behind your thumb—all the history of the Earth and all the people you knew and all the problems. It is merely a small body that’s orbiting a rather normal star, and it just happens to be at the proper distance with proper mass to support life.
And then I thought how insignificant we really are. The Sun itself is tucked away in the outer edge of a galaxy called the Milky Way, and that’s only one of millions of galaxies in the universe. And here’s this little body sitting out there 240,000 miles away, and I thought, “Boy, how fortunate we all are to have a spot like that to go back to, and hopefully, we can make it back home.”
(Quoted from page 26 of Astronomy, June 2015 issue.)