[Apollo 8]

A PHOTOGRAPH OF THE MOON FROM HUMANITY’S FIRST LUNAR VOYAGE, TAKEN CHRISTMAS DAY 1968 

Apollo 8 was the first crewed spacecraft to successfully orbit the Moon and return to Earth. The service propulsion system (SPS) engine was ignited 69 hours, 8 minutes, and 16 seconds after launch, and burned for 4 minutes and 7 seconds, placing the Apollo 8 spacecraft in orbit around the Moon. The length of the burn was essential: if it failed to last long enough, the spacecraft might have been flung off into space; if it had lasted too long, the crew would have risked hitting the Moon.

The Transearth Coast (TEC) was the final phase of the mission. Apollo 8 orbited the Moon ten times before executing an engine burn needed to reach trans-Earth injection orbit. They completed this maneuver out of communication range with Earth due to their trajectory behind the Moon. When the spacecraft returned within range of communication on their Transearth coast, it was Christmas Day in Houston, Texas.