The astronauts had spun around the moon a few times already, their gaze pointed down on the gray, pockmarked lunar surface. But now as they completed another orbit of the moon on Christmas Eve 1968, Frank Borman, the commander of the Apollo 8 mission, rolled the spacecraft, and, soon, there it was.

Earth, this bright, beautiful sphere, alone in the inky vastness of space, a soloist at the edge of the stage suspended in the spotlight.

"Oh, my God," exclaimed Bill Anders, the lunar module pilot. "Look at that picture over there! There's the Earth coming up. Wow, is that pretty!"

Anders knew black and white film wouldn’t do it justice. But he also knew he didn’t have a lot of time if he was going to get the shot.

"Hand me a roll of color quick, will you," he said.

"Oh, man, that's great," said Jim Lovell, the command module pilot and navigator.

“Hurry,” Anders pleaded. “Quick!”

Anders loaded the color film into his Hasselblad camera and started firing away while his anxious crewmates remained transfixed by the blue and white vision outside their windows.

"You got it?" Lovell asked.

He did.

_ _ _

They splashed down in the Pacific on Dec. 27.

Two days later, the film was processed, and NASA released photo number 68-H-1401 to the public with a news release that said: "This view of the rising earth greeted the Apollo 8 astronauts as they came from behind the moon after the lunar orbit insertion burn."

The press recognized immediately the power of the image, Earth, a brilliant oasis in a desert of darkness. The New York Times ran it on its front page above the fold. The Washington Post followed a day later. Life magazine ran a photo essay with a double-page spread of the image and lines from James Dickey, the former U.S. poet laureate:

"Behold/ The blue planet steeped in its dream/ Of reality."

"Earthrise," as it would be called, went viral, or as viral as anything could in 1968, a time that saw all sorts of photographs leave their mark on the national consciousness, most of them scars: The South Vietnamese general pointing his pistol at the soldier's head, point blank; the busboy tending to Robert F. Kennedy's lifeless body; the civil rights activists on the motel balcony pointing in the direction of Martin Luther King Jr.'s killer.

"Earthrise" was something different. A balm for a nation torn by the war in Vietnam, the civil rights movement, protests and assassinations.

In the foreground, there was the "magnificent desolation" of the lunar surface, as Buzz Aldrin would later call it - a lifeless planet, devoid of color, juxtaposed with a distant cousin in the background, as radiant as spring, brilliant in blue and white.

There had been images of Earth shot from space before. But those images were mostly black-and-white, and blurry. They lacked the vividness of Anders's picture, the still simplicity, and the emotion that could perhaps be explained by the fact that the many of the previous photographs had been taken by robots and "Earthrise" by a human - "a thrilled, probably homesick astronaut with a finger on the trigger of this Hasselblad," as Stewart Brand, the founder of the Whole Earth Catalog, put it in an interview.

Brand had been seeking an image such as this, one that could galvanize the country and touch off a movement. He had led a campaign, asking, "Why haven't we seen a photograph of the whole earth yet?"

And here came "Earthrise": a photo at once perfect and humanly imperfect - the tilted horizon, Earth slightly off-center, a rare moment of imprecision during a mission that relied on exact measurements from its military-trained astronauts.

In the photo, Earth is an island with a geography both strange and familiar. There is Africa peeking out from under the clouds, but North is over to the right, not up, a world made topsy-turvy by the disorienting distance of 240,000 miles.

The United States had set off on this improbable journey to vanquish the Soviets, to claim the ultimate high ground and the national superiority that would come with it. In their flight suits and crew cuts and all-American probity, the astronauts were the arm of the nation's might, a projection of power. They returned, of course, from the breach victorious - the first men ever to leave Earth's orbit and take a few laps around the moon.

Their triumph, celebrated in ticker tape, was to be measured in the fiery thrust of the Saturn V rocket propelling them deeper into space than anyone had gone before. But it was also found in the unexpected discovery captured in this simple photograph buried in the rolls of film they brought home - land masses without boundaries, the thin layer of the atmosphere, a unifying expression of vulnerability, something that as Pope Paul VI would say, recalled "the dumbfounding proportions of the universe in relation to our infinite smallness."

Turns out the military pilots turned astronauts were artists as well.

"Earthrise" soon replaced another dominant image from the time, the mushroom cloud.

"Its iconic power went away, at least in representing modern times," Brand said. "In the course of a couple years, you had a universal icon based on fear give way to a universal icon based on what people thought of as hope and excitement."

"Earthrise" also helped fuel the environmental movement. Which was ironic since so many environmentalists in the 1960s were steadfastly against the Apollo program. Why spend all this money going to space when there are real problems here on Earth?

The first Earth Day was held some 16 months later, and today the image endures as a uniting symbol.

"As I looked down at the Earth, which is about the size of your fist at arm’s length, I’m thinking, ‘This is not a very big place. Why can’t we get along?’ " Anders said during a video played recently during a ceremony at Washington National Cathedral celebrating the 50th anniversary of the mission. “To me it was strange that we had worked and had come all the way to the moon to study the moon, and what we really discovered was the Earth.”