On December 21, 1968, Apollo 8, the first manned mission to the moon, blasted off from present-day Cape Canaveral in Florida. The plan called for the three astronauts onboard to come within about 70 miles of the moon, circle it several times and return safely home, all while broadcasting their feats to the world below. By gaining operational experience, testing equipment and checking out potential landing sites, they also hoped to pave the way for a moonwalk the following year, just in time to meet former President John F. Kennedy’s challenge to do so before the end of the decade.

Up until then, the United States had undergone an extremely turbulent and polarizing year: Martin Luther King Jr. and Robert F. Kennedy had been assassinated, the war in Vietnam had escalated and race riots had broken out in cities across the country. Yet citizens of all stripes united in support of Apollo 8. Tens of thousands of spectators turned out the morning of the launch, including two Supreme Court justices and aviation pioneer Charles Lindbergh, and newspapers went giddy over humankind’s potential. The New York Times, for instance, called Apollo 8 “the most fantastic voyage of all times.”

Minutes after a straightforward departure, Air Force Col. Frank Borman, the mission commander; Navy Capt. James A. Lovell Jr., the command module pilot; and Air Force Major William A. Anders, the lunar module pilot, eased into Earth’s orbit in order to check for spacecraft damage. Finding no problems, they then propelled themselves into uncharted territory, voyaging for three days through the vastness of space. No previous manned flight, either U.S. or Soviet, had ever left Earth’s gravitational field. On December 24, the astronauts became the first humans to see the dark side of the moon and the first to enter lunar orbit, circling the celestial body 10 times. By then, they had also become the first to see the Earth from afar as a whole planet, a viewpoint Anders famously captured in his “Earthrise” photo.

Under the insistence of NASA administrators and public-relations specialists, the Apollo 8 crew hauled a TV camera up into space with it, doing six live broadcasts over the course of the mission. The first two took place on the way to the moon, including one in which Lovell wished his mother a happy birthday. Two more took place on the way home, and another was televised from lunar orbit early on Christmas Eve morning (when many Americans were still sleeping). All essentially served as undercards for the fourth of the six broadcasts, which aired on Christmas Eve from about 9:30 to 10 p.m. EST, right in prime time. According to TV Guide, this showing attracted an audience of about a billion—or roughly one of out of every four people on the planet.

As Apollo 8 rounded the moon for a ninth time, Borman got the prime-time Christmas Eve broadcast started by saying the crew would take the audience with it through a lunar sunset. He described the moon as “vast,” “lonely” and “forbidding,” and added that it “would not appear to be a very inviting place to live or work.” Lovell chimed in that the “vast loneliness of the moon is awe-inspiring, and it makes you realize just what you have back there on Earth.” Anders, meanwhile, declared himself quite impressed with lunar sunrises and sunsets.

Pointing their camera out the window, the astronauts next began a running diary of what they could see, from the pitch-black sky to the moon’s various mountains, craters and seas. To conclude the broadcast, they took turns reading the opening verses of the Bible. Borman then signed off, saying, “Good night, good luck, a Merry Christmas and God bless all of you, all of you on this good Earth.” As Borman and Lovell later explained, they got no instructions from NASA except to do something “appropriate.” They said they selected this particular passage from the Book of Genesis because it was the foundation of “many of the world’s religions,” not just Christianity. (Not everyone agreed with the choice; a well-known atheist filed a lawsuit over the reading.)

Shortly past midnight on Christmas morning, the crew ignited an engine burn to leave lunar orbit and start for home. Lovell announced the burn’s success, telling an anxious mission control, “Please be informed there is a Santa Claus.” The astronauts then settled down to a Christmas dinner of real—not freeze-dried—turkey and stuffing, plus miniature bottles of brandy. On December 27, they reentered Earth’s atmosphere at speeds of more than 24,000 miles per hour and splashed into the Pacific Ocean, where an aircraft carrier picked them up. As intended, the mission begot even greater successes. Fewer than seven months later, on July 20, 1969, Neil Armstrong and Buzz Aldrin stepped out onto the lunar surface.