A depection of Apollo 8’s insertion into lunar orbit, by artist Mark Karvon.

Humanity has staged, to date, nine manned missions to the moon. On six of these missions, people walked on the lunar surface. December 21 is the anniversary of the first trans-lunar launch, and the first manned mission to another celestial body, Apollo 8. Her crew was Frank F. Borman, James A. Lovell, and William A. Anders.

Apollo 8 was, in many ways, a hardware test. Even as late as 1969, the nature of the lunar surface wasn’t totally understood. The moon was by then known to be covered with a very dusty soil that we now call regolith. There were still doubts about the possibility of landing a human on the moon, the fear being that any lander would sink into the regolith and become trapped as if in quicksand. This was one of the many questions that Apollo 8 was sent to answer. Was the hardware of the Apollo program suitable for the task of sending humans to the moon and back? Observations from the three astronauts, the first humans to get a good, clear view of the lunar surface, concluded that the existing lander design would work.

But as big a question as the lunar surface was, an even bigger question was the navigation of a trans-lunar flight path. Navigating in outer space is very difficult, even when you’re only in Earth orbit. But when you need to deal with not one celestial body, but two, the potential for problems gets very high, very fast. The flight calculations for Apollo 8 were extensive, and needed constant adjustment. But the crew of the spacecraft, and the ground support crew, handled everything in stride. It took Apollo 8 three days to reach the moon. The craft orbited the moon ten times over a roughly eighteen-hour period, then broke orbit for the three day journey home. The return flight began early on Christmas morning, shortly after 6 AM UTC. The craft splashed down on December 27.

The flight of Apollo 8 has been largely overshadowed by the later flight of Apollo 11. But it still had great historical significance. Some of the most famous photographs from the early space program, including the iconic Earthrise, were taken by Apollo 8. It was also the first time that humans had traveled beyond the gravitational influence of Earth. The year 1968 had been riddled with tragedies and turmoil all over the world, but many in the press felt that the success of Apollo 8 allowed the year to end on a relatively high note.

The mission also created some controversy when, during their final television broadcast before leaving lunar orbit, the three astronauts took turns reading the creation story from Genesis. This prompted atheist activist Madalyn Murray O’Hair to sue NASA for having astronauts – government employees – pray on the job. This struck her as violating the separation of church and state. (O’Hair was notorious for doing stuff like that.) The suit was eventually thrown out of court, but NASA did tone down such actions on later flights, wanting to avoid more negative publicity.

The information gathered during the flight of Apollo 8, especially the computation of a trans-lunar round trip, proved vital in the success of the successive manned missions to the moon, including Apollo 11. The command module of Apollo 8 is on display at the Museum of Science and Industry in Chicago, Illinois. Other artifacts from the flight are in museums and science centers around the world.