Seconds to go: Aldrin aboard the Apollo 11 lunar module, Eagle, preparing to land. Image: NASA

Nothing prepared me for the starkness of the terrain. It was barren and rolling, and the horizon was much closer than I was used to. Earth's diameter is such that its inhabitants have no personal awareness of the curvature; it's easy to understand why, for centuries, it was believed to be flat … but on the smaller Moon, my impression was that we were on a ball; or on the knoll of a hill that extended more than 2 km, and was neatly rounded off. I even felt a bit disoriented because of the nearness of the horizon.

In every direction, the surface was pocked with thousands of little craters and many larger ones, 2 to 15 metres across, and littered with angular rocks. It looked like a collection of just about every variety of shape, angularity and granularity of rock. At first, I couldn't see much colour.

I was particularly struck by the contrast between the starkness of the shadows and the desert-like barrenness of the rest of the surface. It ranged from dusty grey to light tan, and it was unchanging except for one startling sight - our lunar module, with its black, silver and bright orange-yellow thermal coating shining brightly in the otherwise colourless landscape.

The colour of the ground depended on the angle of the Sun. It could be shades of grey, or it could be quite bright if the Sun was at my back. If I looked around my shadow, it gave off a whitish colour. But if I looked towards the Sun, it appeared as a dark as charcoal.

I could look around and see the Earth, which seemed small - a beckoning oasis shining far away in the sky. It was almost straight up and was hard to see because of the stiffness of our spacesuits. I couldn't look directly at the Sun. It was too brilliant - almost like a floodlight of pure white light. The amount of light that reflected off the lunar surface was so high, it was as if we were standing in brilliantly lit snow. The sky was utter blackness - I could see no planets or stars.

I remarked to Houston, "Beautiful, beautiful. Magnificent desolation."

I was full of goosebumps when I stepped down onto the surface. I immediately looked down at my feet and became intrigued with the properties of the lunar dust. On Earth, if you kick sand in the desert, clouds build up as it scatters in all directions, with some grains travelling farther than others. The Moon dust did not cloud at all. Every grain travelled on a precise path from where it was kicked and fell, uniformly, 10 to 12 cm away in a sort of ring. Our boots sank in only a few millimetres in most places, but on the edges of small craters they sank up to 15 cm.

There was about every type of rock imaginable, all covered with a very light powder. The rocks themselves actually had no colour - until you looked closely at the crystals on their surface. The thought briefly occurred to me that these rocks had been sitting there for hundreds of millions of billions of years, and that we were the first living beings to see them.

But we were too busy to be philosophical for long or to study them closely, so we just grabbed what looked like an interesting assortment. I felt them crunch beneath my feet as we walked around.

It felt buoyant on the surface. My Earth weight with backpack and suit was 163 kilos; on the Moon I weighed only 27 kg.

Our suits were marvels of engineering that worked like thermal bottles, but they hampered our activities. When pressurised, they were as hard as a football and made even bending over extremely difficult. The backpack shifted my centre of gravity - I felt balanced only when I was tilted slightly forward.

As planned, I jogged around a bit to test my manoeuvrability. The exercise gave an odd sensation - I felt like I was moving in slow motion. I noticed immediately that my inertia seemed much greater on the Moon than on the Earth. Earthbound, I would have stopped my run in just one step - an abrupt halt. I immediately sensed that if I tried this on the Moon, I'd be face down in the lunar dust. I had to use two or three steps and sort of wind down. The same applied to turning around - on Earth it's simple, but on the Moon, it's done in stages. And the ground gave the impression of being rather slippery, particularly near the craters, where we tended to slip sideways.

I experimented moving around, trying two-legged kangaroo jumps, but it was too tiring. We eventually hit on a lazy lope that covered about a metre with each stride, floating with both feet in the air most of the time. It looked like fun, and it was. But it was also exhausting.

We had a number of experiments to conduct and precious little time to do them. A solar wind experiment had to be assembled and then taken down; experiments to test the seismic characteristics of the Moon had to be set up; a laser reflector had to be deployed; and after all this was done, rock samples had to be gathered. Because of the large variety of unknowns on this first trip, our surface activity was limited to two hours and forty minutes, and every minute was busy.

I've often been asked about fear: when you're that far from home and a million things could go wrong, aren't you afraid? Well, we weren't afraid. True fear is the fear of the unknown, and all our training had been geared towards eliminating the unknown as much as possible. For a month before the flight we'd worked 12 hours a day, at times on a simulated lunar surface, tromping around in a sand-filled 'litter box' that took up slightly less room than a tennis court, with heavy equipment on our backs. As combat pilots and in flight-testing aircraft, we learned to either cope or get out.

I did feel a tinge of stage fright. I think we both did. Perhaps the worst moment was when Houston announced that the President wanted to talk to us. My heart rate, which had been low during the entire flight, suddenly jumped. One quarter of the Earth's people were listening on radio or watching on TV.

We were alone, but the immense feeling of being watched probably hampered our operation slightly. But it also gave us the adrenalin to keep functioning.

My strongest memory of those few hours on the lunar surface was the constant worry that we'd never accomplish all the experiments we were scheduled to do. There wasn't time to savour the moment. It seemed as though what we were doing was so significant that to pause for a moment and reflect metaphysically was really contrary to our mission.

We weren't trained to smell the roses. We weren't hired to utter philosophical truisms on the spur of the moment. We had a job to do.

I do remember that one realisation wafted through my mind when I was up there. I noted that here were two guys farther away from anything than two guys had ever been before. That's what I thought about. And yet, at the same time, I was very conscious that everything we did was being closely scrutinised more than four hundred thousand kilometres away.

As we left the surface to re-enter the spacecraft, we performed a brief ceremony. I reached into my shoulder pocket, pulled out a packet, and tossed it out onto the surface. It contained a patch commemorating the three American astronauts who had perished when their spacecraft was engulfed in an explosive fire during the simulation test for the first Apollo flight. Next there were two medallions in memory of Russian cosmonauts who had also died. And then there was a disc containing messages from the heads of state of 72 countries.

We had thought long and hard to come up with what was - to me - the most important symbol of our flight: the olive branch of peace, carried to the Moon by our spacecraft, the Eagle (named after the American bald eagle). I had four olive branches made of gold pins. We left one on the Moon, and the three of us - myself, Neil Armstrong and Michael Collins (who had been orbiting above on our craft Columbia) - kept one each for our wives on our return.

I thought it would convey a lot more of the significance of our first flight: that the mission was more than just a culmination of a long national effort to reach the Moon by the end of the decade. It carried greater meaning than that.

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