Imagine getting to sit down with Columbus and ask him what he thought and felt as he first set eyes on the New World. That's pretty much how it was for me when I interviewed Frank Borman, Jim Lovell, and Bill Anders, the crew of Apollo 8, who made the first manned voyage around the moon in December 1968. The stories I heard from Borman, Lovell and Anders about their historic voyage were postcards from the edge of human experience. Before Apollo 8, "space travel" was just a figure of speech; they were the first astronauts to actually go somewhere. But as they fired the third stage of their Saturn 5 booster and headed out of Earth orbit, it was the leaving that had the greatest impact.

Speeding onto a course for the moon, the men looked back and saw their world not as a landscape but as a planet: a vivid, deep-blue ball wrapped in brilliant white clouds. Bill Anders found the sight breathtaking—and, for a little while, confusing. As a schoolboy he'd prided himself as being something of a geography expert, but the real Earth looked nothing like the schoolroom globe, and as he said years later, it took him several minutes to figure out which part of the world he was looking at. At first, it appeared about the size of a basketball held at arm's length, but as Apollo 8 sped moonward it dwindled rapidly; 11 hours into the mission it looked no bigger than a baseball.

For Jim Lovell, veteran of two Earth-orbit space missions, the change in perspective was profound. Circling Earth, his frame of reference had been continents and oceans; through Apollo 8's windows he saw celestial bodies. Our world was a little ball off in one direction, the brilliant sun was off in another, and near it, all but lost in its glare, was their goal. Barreling along in its orbit at 2,300 miles (3,700 kilometers) per hour, the moon was a moving target, some 234,000 miles (376,585 kilometers) from Earth at the time of the astronauts' departure. In an extraordinary feat of marksmanship, they would have to fly just ahead of its leading edge and then, firing the Apollo spacecraft's rocket engine, go into orbit just 69 miles (111 kilometers) above its surface. All three men knew there was precious little room for error, and for Frank Borman the most amazing moment of the flight came when Apollo 8 lost radio contact with Earth as it flew behind the moon—at the precise time mission control had predicted; it meant they were right on target.

And then, after a perfect engine firing, Borman, Lovell and Anders were looking down at a sight no human eyes had ever seen: the far side of the moon, a bleached and desolate landscape pockmarked by craters of all sizes. From 69 miles up, looking down at this barren expanse, Borman was reminded of a battlefield; Anders thought of a deserted beach that had been churned by footprints during a volleyball game. Years later, Anders confessed that he had expected a more dramatic scene, thanks mostly to the spectacular moonscapes depicted in the film 2001: A Space Odyssey, which he'd seen before the flight. In comparison, the pummeled terrain he saw through Apollo 8's windows was a disappointment.

But there was nothing disappointing about what the astronauts saw as the spacecraft coasted around from the lunar far side on its fourth orbit: Earth, rising beyond the battered horizon, so tiny that the men could hide it behind an outstretched thumb. But the distance, and the contrast with the moon's lifeless desolation, only magnified its beauty as well as its preciousness as an oasis of life in the endless void. On a flight in which every event had been planned to the second and practiced until it was second nature, here was an unveiling the astronauts had never anticipated. Anders, whose photograph of Earthrise would become an icon of the 20th century, would later find in that image a paradox: NASA had sent him and his crewmates all that way to explore the moon, he would say, but the most important thing they had discovered was Earth. The "Earthrise" photo came to symbolize the leap humans had taken with the first voyage to another world.

Even before the astronauts had returned to their home world, the impact of that leap was being felt. The day they spent circling the moon was Christmas Eve, and for many, that added to the wonder of the event, especially when the astronauts read the first 10 verses of Genesis during a live telecast from lunar orbit that night. For the first time in the history of exploration, millions of people witnessed the event as it unfolded. And for NASA, Apollo 8 turned out to be the mission that won the space race with the Soviet Union: Although seven months remained before Neil Armstrong and Buzz Aldrin would walk on its surface, Apollo 8 had cleared the way for that next "giant leap for mankind."