Forty years ago, on 20 July 1969, Neil Armstrong and Buzz Aldrin became the first human beings to walk on the Moon. Here are 10 things you might not have known about Apollo 11, humanity's "one priceless moment".
1. All three crew members - Neil Armstrong, Buzz Aldrin and Mike Collins - were born in the same year: 1930. All three were pilots (Collins and Aldrin in the USAF, Armstrong in the Navy). But there the similarities ended. Collins and Aldrin were from military "blue blood" families, Armstrong from small town Ohio. Collins dubbed the crew "the amiable strangers".
2. It was never a foregone conclusion that Apollo 11 would make the first lunar landing. Each Apollo mission had to fulfil various objectives. But if, for instance, Apollo 10 had failed in its mission, testing the lander (called the LM) in lunar orbit, then the task would have passed to Apollo 11. That would have given the first lunar landing attempt to Apollo 12 and made another, very different, astronaut, Pete Conrad, the first man on the Moon.
3. Neil Armstrong might never have been the one to take that historic "one small step". It might have been his lunar module pilot, Buzz Aldrin. During the Gemini missions, the mission commander stayed in the capsule while the pilot carried out the spacewalks. Initially Nasa - and Aldrin - thought the same would happen on Apollo. But Nasa managers were worried about the image of the first man on the Moon, a man who would become the next Christopher Columbus or Orville Wright. Aldrin had not won many friends at Nasa because of his forthright style - "he was a burr in the saddle", said one senior manager. But Armstrong - the strong, quiet, courageous all-American hero - was a natural choice. Nasa changed the rules and told Armstrong he would be first out of the lunar module. (Aldrin was furious and later drew up plans for a lunar lander with two doors that would allow the astronauts to get out at the same time.)
4. Armstrong was almost killed in the weeks leading up to the mission. The commander practised for the lunar landing in a contraption called the lunar landing training vehicle (LLTV), dubbed the Flying Bedstead. Using jets, it mimicked the Moon's gravity to give the Commander a realistic experience of what a lunar landing would be like. Armstrong practised on it tirelessly. But in May 1968, the machine went berserk. He tried in vain to bring it under control but failed. At just 100ft, he hit the eject button a second or so before the LLTV crashed to the ground and was destroyed in a fireball.
5. Each crew member was allowed to take personal items on board. Some of these could be sold later in lieu of the life insurance policies which, unsurprisingly, were hard to come by for Apollo astronauts. Armstrong took with him some pieces of wood from the Wright Flyer, which had made the first powered flight in 1903. There were also commemorative medals for the crew of Apollo 1, who had died in a fire on board their Command Module during a routine ground test, and the dead Soviet cosmonauts, Vladimir Komarov and Yuri Gagarin. (In fact, Valentin Bondarenko was the first man to die in the space race, but it wasn't until 1980 that the world learned of his grisly death in a fire in an oxygen-filled pressure chamber during an endurance experiment.)
6. The Apollo 11 mission could have ended in failure because of a series of relatively harmless computer programme alarms that went off as the lunar module was descending to the surface. It was saved thanks to a rehearsal weeks before the mission. Mission controllers were put through their paces in a series of practice runs, simulating a lunar landing. On the final day, one of the controllers called an abort because of a simulated computer program alarm. It had been the wrong call. But it meant that when there were similar alarms during the actual Apollo 11 landing, the same controller knew he could ignore them and allow the landing to continue.
7. When the lunar module Eagle was still 20ft above the surface, Armstrong and Aldrin were told they had only 30 seconds of fuel left. If they still hadn't landed by then, Mission Control would have ordered Armstrong to abort the landing. But would he have? Back on Earth, Armstrong revealed: "If I'd run out of fuel, why, I would have put down right there. I could fall from a fairly good height, perhaps maybe 40ft or more in the low lunar gravity, the gear would absorb that much fall. So I was perhaps probably less concerned about it than a lot of people watching on Earth." (As it turned out, after the mission Nasa calculated that Eagle could have flown for at least another minute.)
8. When Armstrong made his famous announcement that the landing had been "one small step for man, one giant leap for mankind", he had actually meant to say "one small step for a man" but it had come out wrong. Considering it is one of the most famous quotations in human history, Armstrong has always been typically sanguine about it. "I thought about it after landing," said Armstrong afterwards, "and because we had a lot of other things to do, it was not something that I really concentrated on but just something that was kind of passing around subliminally or in the background. But it, you know, was a pretty simple statement, talking about stepping off something. Why, it wasn't a very complex thing. It was what it was."
9. There were many firsts about the Apollo 11 mission, but two of the most notable were the responsibility of Buzz Aldrin. He became the first human being to celebrate Holy Communion away from the Earth, and the first to urinate on another world.
10. Just in case the mission had ended in disaster, President Richard Nixon had prepared a suitable valedictory speech. It spoke of how "fate has ordained that the men who went to the Moon to explore in peace will stay on the Moon to rest in peace". It would have meant Mike Collins, the command module pilot, would have had to make the loneliest journey home; but from that time onwards "every human being who looks up at the Moon in the nights to come will know that there is some corner of another world that is forever mankind".