Fifty years ago, two men first set foot upon the surface of the Moon. That's a very simple sentence to write, but getting to grips with what is almost certainly one of the top five events in the whole of human history – perhaps even for life on Earth – is not so easy. The Apollo 11 Moon landing on July 20, 1969 has become an integral part of our history, our folklore, and even our popular culture, but it's still hard for those who didn't witness it live to appreciate what a pivotal, world-changing thing the conquest of the Moon was. Even that momentous phrase said by Neil Armstrong has, over the past half century, become a cliché, a catch phrase, and even a punchline. On its fiftieth anniversary, let's relive this momentous event.

Watching history

On July 20, 1969, a 10-year old boy was sitting in his pajamas in front of the flickering screen of a black and white Pye television set, where he would sit until well into the early hours of the morning. Too tired to stay awake and far too excited to sleep, I'd already missed watching the momentous launch of the Apollo 11 mission four days earlier due to grandparents who gave a higher priority to a fishing trip than one of history's greatest events. I was determined not to miss the first footsteps on the Moon.

Surrounded by the plastic models that I'd assembled of the Command Service Module (CSM), the Lunar Module (LM) and even a frighteningly large and rickety one of the Saturn V rocket, I strained hard as I watched the first blurry television pictures from the Moon and tried to understand the calm, monotone American accents distorted by radio transmission. I failed half the time and was very thankful the BBC commentators translated NASA English into British English.

Even at that age, I, along with the billion or so other people who watched Neil Armstrong step off the Lunar Module or listened to it on the radio, knew that this was something momentous. This was something that never, in any way had happened before. Columbus has counter claimants to the discovery of the New World. There were even those who argued that Sir Edmund Hillary and Tenzing Norgay weren't the first to conquer Everest. But this was a true first. This was the proverbial Giant Leap. The human species had left its home.

Journey to the Moon

Apollo 11 began its journey on July 16, 1969 at 13:32 GMT as the two spacecraft and their crew of three NASA astronauts lifted off on the fiery tail of a skyscraper-sized Saturn V rocket from Launch Complex 39A at the Kennedy Space Center in Florida. About one million people were present to see the launch in person, including US Vice President Spiro Agnew, former US President Lyndon B. Johnson and his wife Lady Bird Johnson, Chief of Staff of the United States Army General William Westmoreland, members of the US cabinet, 19 state governors, 40 mayors, 60 ambassadors, 200 congressmen, and 3,500 reporters from around the world.

Strapped in their couches inside the Command Module were Mission Commander Neil A. Armstrong, Command Module Pilot Michael Collins, and Lunar Module Pilot Edwin "Buzz" E. Aldrin, Jr. All were veteran astronauts with one flight under their belts, though their choice as crew for Apollo 11 was due strictly to NASA's complicated astronaut rotation system.

Why go to the Moon?

According to NASA's official press materials for the mission, the mission's prime objective was very simple. It was to "perform a manned lunar landing and return." Indeed that was the objective, but those seven words covered a lot more. Apollo 11 was the final push in a bloodless battle of the Cold War, a decades long competition between the United States and its allies versus the Soviet Union for dominance of the Earth.

For years, the Space Race to put the first man on the Moon had been a close-run thing with the Soviets often scoring many spaceflight firsts over the Americans, but NASA now seemed certain to succeed. However, the space agency had little knowledge of what was going on behind the Iron Curtain or the status of the Soviet Moon effort, so the race was very much on.

Landing on the Moon

The outward voyage of Apollo 11 had been uneventful. Thanks to the previous Apollo missions that had rigorously flight tested all of the spacecraft and procedures as well as making two pathfinding orbital visits to the Moon, there were no unpleasant surprises. Everything worked as advertised and Apollo 11 entered lunar orbit on July 19, 1969 at 17:21 GMT.

The undocking

After a day of course corrections and preflight checks, the Lunar Module (LM) separated from the Command Service Module on July 20, 1969 at 17:44 GMT. The former was now known by its radio call sign of "Eagle" and the latter by "Columbia." Aboard Eagle were Armstrong and Aldrin, while Collins was left behind in Columbia to tend to the ship, make observations, and act as a communications backup relay. As the two craft parted, Armstrong radioed to Mission Control, "The Eagle has wings."

Descent

So far, Apollo 11 seemed almost routine, but that changed as Eagle, partly under control of the onboard computer and partly by Armstrong, fired its Descent Engine and killed the forward speed of the vehicle, sending the LM moonward. Unfortunately, for reasons that still aren't completely clear, they were flying slightly faster than they should, meaning that they'd overshoot the planned landing site.

Meanwhile, the television viewers back on Earth listened to the radio chatter between the astronauts and Mission Control. Because there was no live video feed, many television news services provided some surprisingly good model and animation simulations for the time.

Computer error 1202

The biggest problem during the landing was with the onboard computer that controlled flight almost until landing. Five minutes after starting the engines, the computer flashed 1202 and 1201 error alarms, meaning that the computer was getting too much data and was dumping all but the highest priority information. This was later found to be due to the rendezvous radar being left on, but, at the time, Mission Control was more worried that the computer itself might be at fault and a split-second decision was needed for whether to continue with the landing or not.

Landing

Then the final decision was made, each man at each console in Mission Control answering "Go" to the request for the GO/NO GO decision. The message was sent by the Capsule Communicator (CAPCOM), "Eagle, you are go for landing."

The Eagle was now four miles (6.4 km) downrange of the landing site, but ahead of schedule. This was a problem, but overshooting wasn't too much of a hazard, since the landing site was more of an ellipse than "X Marks the Spot."

The LM was now in pure powered flight. No gliding, just simple ballistics countered by the engine thrust. Once the rocket was exhausted, Eagle would plummet. Traveling at feet per second, the lander became the slowest flying manned spacecraft in history. But when Armstrong looked out the window, he saw that the computer was sending Eagle into a boulder-strewn area just next to the rim of a 300-ft (91-m) crater.

The low-fuel warning light came on and Armstrong had to find somewhere flat to set down. With the Descent Stage now almost out of propellants, the LM was top-heavy and landing on a rock or a slope might cause it to tip over. At an altitude of 250 ft (76 m), Armstrong guided the LM over another crater. With 90 seconds of flight time left, the engine exhaust was throwing up dust from the surface and Mission Control and the Eagle's crew talked back and forth.

CAPCOM: 60 seconds.

EAGLE: Lights on. Down 2-1/2. Forward. Forward. Good. 40 feet, down 2-1/2. Picking up some dust. 30 feet, 2-1/2 down. Faint shadow. 4 forward. 4 forward, drifting to the right a little. 6 (garbled) down a half.

CAPCOM: 30 seconds.

EAGLE: (garbled) forward. Drifting right. (garbled) Contact light. Okay, engine stop. ACA out of detent. Modes control both auto, descent engine command override, off. Engine arm, off. 413 is in.

CAPCOM: We copy you down, Eagle.

EAGLE: Houston, Tranquility Base here. The Eagle has landed.

CAPCOM: Roger, Tranquility, we copy you on the ground. You've got a bunch of guys about to turn blue. We're breathing again. Thanks a lot.

It was July 20, 1969, 20:17 GMT.

Eagle was on the Moon.

Tranquility Base

Tranquility Base was now the call sign for that unbelievably small, fragile, and lonely craft sitting on the vast, flat lava plain of the lunar mare. The name was Armstrong's idea, which he sprang on Mission Control without warning, catching the CAPCOM by surprise, who stammered over the words.

It got its name from the landing site, Mare Tranquillitatis (Sea of Tranquility) at latitude 0.67408°N and longitude 23.47297°E. It had been chosen because the great sea of hardened lava was flat, with few craters, hills, crevices, or boulders – though not few enough. Being on the equator, it required the least amount of fuel to visit. It had good visibility and the landing was timed for the lunar early morning, so the angles would be good for photography and the surface wouldn't be too hot for the astronauts' plastic overshoes to handle.

But no one aboard Eagle, Columbia, or at Mission Control was relaxing or celebrating just yet. Eagle may have landed, but the decision had to be made to stay or to order the crew to abort the mission immediately. After a quick instrument check and consultation with the experts, Armstrong and Aldrin were cleared to stay and they began the next checklist for shutting down the flight systems until needed again.

One Small Step for Man

The original plan was for the astronauts to rest a few hours before leaving the spacecraft, but both men were far too excited to wait and couldn't relax if they tried. So, about three and a half hours after landing, they began preparations for ExtraVehicular Activities (EVA).

Based on their training, this was supposed to take only two hours, but it was more like three and a half because the LM's cabin was cluttered with checklists, food packets, tools, and other miscellaneous items that needed stowing away. Until then, they couldn't move around properly to suit up.

Who goes first?

So how did NASA decide who would be the first to set foot on the Moon? On previous spacewalks, the commander had stayed inside the ship while the pilot went outside. When Apollo 11 was planned, it first seemed that Aldrin would go first, but the honor was eventually given to Armstrong. Why is still not entirely clear and there are many versions of the story. Some say that Aldrin had heard that Armstrong was chosen and started lobbying for himself, only to have astronaut chief Deke Slayton select Armstrong to quell any rivalry.

Other stories claim that it was easier for Armstrong to get out first due to the LM's cabin layout. Still others say that NASA preferred Armstrong's Lindbergh-like temperament as more suited to being the first man on the Moon.

On the ladder

Perhaps the most maddening part of the mission for the public, especially the under-11s, was Neil Armstrong climbing down the ladder. He opened the EVA hatch at 02:39 GMT and took 16 minutes to get down. This was because no one had ever done such a thing in a bulky space suit at on-sixth Earth gravity, so Armstrong was taking things very slowly and deliberately.

Actually, he was lucky to have a ladder. Originally, the LM didn't have one and the astronauts were expected to shinny down a rope. Fortunately, this turned out to be impractical, so Armstrong had a more dignified descent.

As he climbed down, he paused to pull a D-ring that unlatched the Modular Equipment Stowage Area (MESA), a swing-down bay with exploration equipment and a black and white camera that was already plugged in, turned on, and pointing at Armstrong. The camera was (almost) state of the art for its time, but it was a slow-scan system that wasn't compatible with conventional television formats, so those of us watching were actually seeing low-definition video that was being viewed off an Earthside monitor screen by a second TV camera for broadcast.

It was like watching the whole thing through an aquarium badly in need of a good clean, but it could have been worse if it weren't for the Australian connection. During the first nine minutes of the Moonwalk, the television transmissions from Eagle were received by three NASA ground stations, but when they switched to the Parkes Radio Telescope and the Honeysuckle Creek tracking station near Canberra, the picture quality was so good that NASA decided to stick with it for the remainder of the EVA.

What's even more impressive is that the radio dish that day was fighting with a violent squall and high winds of 70 mph (110 km/h) hitting it as it sat pointing at the horizon Moon like a great sail. This taxed the integrity of the station's supports and caused gears to slip as wind alarms sounded in the control room, but the US and Australian technicians kept their heads until the winds died down.

At 02:55 GMT, Armstrong stepped off the ladder and landed on the pad of one of the legs of the Decent Module's undercarriage. Describing the surface as "almost like a powder," he examined the lunar surface for a minute.

ARMSTRONG: I'm at the foot of the ladder. The LM foot pads are only depressed in the surface about 1 or 2 inches. Although the surface appears to be very, very fine-grained, as you get close to it. It's almost like a powder. Now and then, it's very fine.

ARMSTRONG: I'm going to step off the LM now.

ARMSTRONG: That's one small step for a man. One giant leap for mankind.

It was July 21, 1969. The time was 02:56 GMT.

But hang on, the transcript says, "That's one small step for a man," not "That's one small step for man." That's been a bone of contention for half a century. NASA and Armstrong claim that he said "a man" and not "man," while the accepted version leaves out the "a". Some have argued that Armstrong misspoke, but others claim that there was a transmission error that garbled the "a" and blanked it out. What really happened? We may never know.

But there was so much to do and very little time to do it. Armstrong quickly gathered up a small bag of soil and tucked it into a pocket of his suit in case they had to abandon the EVA. Then the television camera had to be moved to provide a view of the astronauts as they worked.

The first tasks were slow and deliberate, taking several minutes as mission control constantly and closely monitored Armstrong's health and suit condition. Meanwhile, Armstrong became the first person to learn how to move in low gravity outside of a simulator. He started taking pictures with the Hasselblad camera mounted on his spacesuit to provide a detailed record of the day.

Aldrin follows

At 03:11 GMT, Aldrin left the LM, saying that he'd be careful not to lock it behind him. He stepped off the ladder and then easily hopped the three feet back up in the low gravity. Then he looked around and said, "Magnificent desolation."

With both men on the surface, a plaque attached to one of the lander legs was unveiled. It had images of the two hemispheres of the Earth and the inscription, "Here men from the planet Earth first set foot upon the Moon, July 1969 A.D. We came in peace for all mankind."

This was followed by planting the US flag and the two Moonwalkers, along with Collins in the Command Module, taking the longest-distance-ever Presidential phone call as Richard Nixon congratulated them from the White House with a 159-word speech.

The preliminaries done with, Armstrong and Aldrin deployed a raft of scientific experiments, including a seismometer and a laser reflector that would allow Earth scientists to precisely measure the distance to the Moon. They also made a visual inspection of the LM, practiced how to move in low gravity, and observed how well their suits worked in the harsh lunar sun.

In addition, the astronauts collected 47.51 lb (21.55 kg) of geological samples – the first of the famous Moon rocks. They are literally as common as dirt, yet are priceless in their cost to procure and their significance.

To the viewers back on Earth, there was something mysterious, almost arcane about the astronauts as they wandered about their various tasks and set up bits of scientific apparatus that were meaningless to most people. It was almost as if they were as alien as the world they were exploring.

Return to the LM

It's hard to believe, but the first and only Moonwalk of Apollo 11 lasted only two hours, 31 minutes, and 40 seconds. Of this, Aldrin only spent one hour and 33 minutes on the surface before climbing back into the LM, followed by Armstrong 41 minutes later after he loaded samples and unloaded surplus gear, including a camera, their boots and backpacks, and other items. Neither had gone more than 300 ft from their ship. The hatch was sealed and the LM repressurized at 05:01 GMT.

The two astronauts then settled down as best they could in the cramped cabin for a meal and seven hours of sleep.

The most dangerous moment

For the public, what came next was an anti-climax, but for the astronauts, their families, and NASA it was the most frightening because their chances of coming home had been calculated at even odds.

To leave the Moon, the Ascent Stage would fire its single engine, leaving the Descent Stage behind as it climbed into orbit. The only problem was that the Ascent Engine was the only part of the LM that had never been tested fully – this could only be done on the Moon itself.

This meant that there was a real chance that the engine might malfunction and fail to ignite. If that happened, Armstrong and Aldrin would be trapped on the Moon without any hope of rescue. The US government was so aware of this that the President had a speech ready and a special memorial service was already written. If the worst happened, NASA would shut down all communications, a clergyman would "commend their souls to the deepest of the deep," and the men would be left to their own devices.

One myth that later sprang up was that Armstrong and Aldrin were given suicide pills just in case. The astronauts denied this, saying that there were far too many ways to die quickly and painlessly on a spacecraft without resorting to cyanide capsules.

Oddly, there almost was a problem when Aldrin accidentally damaged the arming circuit breaker for the Ascent Engine. A bit of ingenuity and a felt-tip pen managed to work the switch and at 17:54 GMT, Eagle lifted off after 21 hours, 31 minutes on the Moon.

As they ascended, Aldrin saw the flag flap wildly and topple over. It had been planted too close in too hard a spot and fell over in the rocket blast. There have been arguments about whether some future visitor should set it back up or leave it where it lies, but that's academic. After half a century, the UV radiation from the Sun long ago reduced it to a thin layer of bleached nylon dust.

Coming Home

What was left of Eagle redocked with Columbia on July 21 at 21:35 GMT. The next day, at 04:55 GMT, the CSM fired its main engine and Apollo 11 was on its way home. It splashed down in the Pacific Ocean on July 24 and the Columbia and its crew were recovered by the aircraft carrier USS Hornet.

Armstrong, Aldrin, and Collins looked like Martians as they returned. Fearing contamination by some unknown lunar germs, the astronauts were dressed in special bio-isolation suits and were herded directly from their helicopter to a huge metal caravan that acted as an isolation chamber while they were in quarantine as they, their spacecraft, and their samples were transported to the Lunar Receiving Laboratory (LRL) in Texas.

Not exactly the most dignified homecoming, but perhaps suitable for the end of such an epic adventure.

One Giant Leap For Mankind

So, what was Apollo 11? A great adventure? A Cold War victory? A huge step in aerospace engineering? A new chapter in exploration and discovery? The first step that will one day see human civilization sweep across the stars? Or was it, as its detractors said, a vainglorious bit of superpower posturing and a vast waste of money and talent as tacky as a Roman triumph and as pointless as the Great White Fleet?

Perhaps it was all of these and more. To one small boy who watched those fuzzy images live, it was the rarest of privileges – bearing witness to history. An event that, whatever the motivations of some, showed just how remarkable the human race can be, and what we can achieve when we put our collective mind to something. For so much of our history people looked at the Moon in wonder as something beyond our reach, but after that fateful day 50 years ago, our reach was extended further into the universe forever more.

Perhaps Apollo 11 is best summed up by that strange mixture of madness and courage in the human heart that faces the unknown with the determination "To strive, to seek, to find, and not to yield."

The video below recaps that historic day.

Read about the fascinating story of the Apollo missions that led up to the first Moon landing.