It isn't the most famous image from the Apollo 8 mission, nor the best. But above is the first photograph of the full Earth taken by a human being.
Frank Borman, Jim Lovell, and Bill Anders were barely three hours into their historic first voyage to the moon, and the S-IVB booster that pushed them out of Earth orbit had just separated from their spacecraft. When the astronauts grabbed cameras to document the drifting rocket stage, they saw the Earth starting to get smaller out their windows as they sped toward the moon (start reading here at the 3:21:46 mark).
From Mission Control, astronaut Mike Collins (who originally was to have flown on this mission instead of Lovell) asked the Apollo 8 crew "Give us a clue as to what it looks like from way up there." Lovell answered, "Well, Mike, I can see the entire Earth now out of the center window. I can see Florida, Cuba, Central America, the whole northern half of Central America, in fact, all the way down through Argentina and down through Chile." Here's the sequence of color photos he and his crewmates shot. Although satellites had previously returned images of the full Earth from high orbit, this was the first look back at the home planet recorded by people heading somewhere else.
Andrew Chaikin recalled the moment in his book A Man on the Moon:
At first, the sight of the third stage itself—a hulking cylinder aglow in the unfiltered sunlight of space—caught their attention. But then, as the spacecraft turned, Borman's crew could see the place they left behind, not a landscape but a planet, a luminous sphere whose roundness was apparent to the eye. Apollo 8 was departing at such fantastic speed that the men could see their world receding from them almost as they watched. Already the entire globe fit neatly within the round window of the command module's side hatch.
Whatever names humans gave their earth, it deserved to be called the Blue Planet, for its dominant aspect was the vivid, deep blue of oceans. In striking contrast were the clouds, brilliant white flecks and streamers that embraced the globe, swirling along coastlines and across oceans. Where land masses peeked through, the vivid oranges and tans of the deserts were easy to spot. More elusive were the jungles and temperate zones; because their verdant hues did not easily penetrate the atmosphere, they showed up as a bluish gray with only a hint of green. And everywhere, beyond the planet's bright, curved edge, a blackness so deep as to be unimaginable.
Happy Earth Day, everyone.