Earthrise over the moon as photographed by the crew of Apollo 8 on December 24, 1968.
On Christmas Eve 1968, my family gathered around the television set as usual to watch the classic Alastair Sim version of A Christmas Carol. But this was no ordinary Christmas, for the movie was interrupted for a special broadcast from lunar orbit. The three astronauts of Apollo 8 showed views of the bleak surface of the moon, and taking account of the occasion, they wrapped up their broadcast by reading the first verses of Genesis.
While the first Moon landing on Apollo 11 is the best remembered moment of the 1960s space race, the flight of Apollo 8 on that Christmas 45 years ago is just as memorable. This was the first space flight to carry humans away from low Earth orbit and the first to take humans into orbit around the moon. The astronauts saw and photographed many unforgettable sights - most famously the whole Earth in the blackness of space.
Apollo 8 was originally planned to be the first test flight of the full Apollo spacecraft, but delays in production of the lunar module meant that the flight as planned would face lengthy delays. NASA officials were also informed from intelligence sources that the Soviet Union was pushing hard to send cosmonauts around the moon and steal a march on the Americans in the race to our closest celestial neighbour.
The solution to both problems was to launch Apollo 8 into lunar orbit with a command and service module but no lunar module, preserving Apollo's schedule and protecting the American lead over the Russians in the space race. The decision was controversial inside NASA, but Apollo 8's commander, Frank Borman, agreed to the plan on behalf of his crewmates, James Lovell and Bill Anders. The flight would be highly dangerous - it would be the first crewed flight launched by a powerful Saturn V rocket, and the crew's flight around the moon would lack the extra margin of safety provided by the lunar module, a margin that would later save the lives of the Apollo 13 crew.
Apollo 8 lifted off on schedule on December 21, 1968, from the Kennedy Space Center. Two hours later on its second orbit of the Earth, the Saturn's third stage engine lit up and sent Borman, Lovell, and Anders to speeds and altitudes never reached before by humans.
After the astronauts tried but failed to show the whole Earth as part of their first television broadcast the next day, their broadcast on December 23 featured views of Earth as a distant planet. As the astronauts neared the Moon, each realized that they could hide the Earth - including everyone and every place they knew and loved - behind their thumb.
On December 24, Apollo 8 passed behind the moon and fired its engine to put the spacecraft into lunar orbit. For the next 20 hours, Borman, Lovell and Anders made ten orbits of the moon during which they scouted out landing sites for future Apollo spacecraft, beamed two television shows back to Earth, the second one capped by the famous Genesis reading, and photographed the moon's bleak surface. And in an unplanned initiative, the astronauts also photographed the Earth rising over the lunar surface.
In the early hours of Christmas Day, Apollo 8 passed behind the moon for a final time. Its engine sent the spacecraft on its way back to Earth, although anxious controllers in Houston had to wait about a half hour to get the news until Apollo 8 came out from behind the moon. On their way back home, the astronauts broadcast more images of their home planet, but it was only after they splashed down in the Pacific Ocean on December 27 that the splendid colour photos of the Earth, the stark shots of moon, and the iconic image of an Earthrise were developed and published.
Seven months later, Neil Armstrong and Buzz Aldrin followed the trail blazed by Apollo 8 and traversed the final 100 kilometres to the lunar surface. Four years after Apollo 8, the Apollo program was over, and humans have been confined to Earth and low Earth orbit ever since. Although the moon has been quiet in the four decades since the last Apollo headed home, the landing of China's Yutu lunar rover on December 14 recalled past lunar exploits and holds the promise of new ones.
It has often been said that the flights of Apollo were planned to explore the moon, but they helped humans better appreciate the Earth. That idea is especially true in relation to Apollo 8.
Regardless of what the future of space exploration has in store, it will be difficult to duplicate that week 45 years ago that married the joy of Christmas with the mystery of humanity's first closeup view of another celestial body.