They set their alarm — metaphorically speaking — for sometime around 10 PM Eastern. Originally the plan had been for them to sleep first, to rest after the landing, and then conduct the moonwalk. But Armstrong and Aldrin — quite reasonably, I think — said they were too keyed up to sleep. Who could sleep? You just landed on the Moon. So Mission Control moved the EVA up.

It took a long time to get ready. Suit up, check everything, depressurize the cabin, open the hatch. The depressurization took a while. We sat in front of the television — my family — watching the coverage. Walter Cronkite in the studio. Scientists and commentators explaining what was happening, what to expect. The picture from the Moon’s surface — black and white, from a camera mounted on the side of the descent stage — was already remarkable. The stark landscape. The shadow of the lunar module. The stillness of a world with no wind, no water, no weather.

At 10:39 PM, the hatch opened. You could see it on the television. The white figure of Neil Armstrong, in his spacesuit, beginning to back out through the hatch and descend the ladder. He moved carefully. There are handholds — specific places to grab — and the ladder itself. He descended, slowly. I counted the rungs, which was silly, but I counted them.

At the bottom: a small platform, and then the footpad of the landing leg, and then the surface. He paused at the bottom of the ladder. He reported what he saw. He tugged on a cord that deployed a camera so the world could watch what came next. And then:

“I’m going to step off the LM now.”

At 10:56:15 PM Eastern time, on July 20th, 1969, Neil Armstrong stepped off the landing pad and placed his left foot in the dust of the Sea of Tranquility. His boot pressed into the fine gray regolith of the Moon. The first human footprint on another world.

He said: “That’s one small step for man, one giant leap for mankind.”

There has been much debate since — even in the days since the landing — about whether he said “a man” or just “man.” The audio has him saying “man,” but Armstrong insists he said “a man,” which makes the sentence grammatically parallel. “One small step for a man, one giant leap for mankind.” I believe him. I think in the most important sentence anyone has said in human history, he said what he meant to say and the radio ate one word. It happens. His meaning is clear regardless.

He spent a few minutes alone on the surface before Aldrin joined him. He described what he saw: fine-grained, somewhat compacted soil. He could kick it loose. His boots sank in only slightly — the surface was solid, just as the Surveyor probes had promised. The footprint held its shape in the vacuum, perfectly crisp. There is no wind on the Moon to erode it. That footprint, or something very like it, is still there tonight and will be there for thousands of years.

Aldrin descended twenty minutes later. He looked around and said something I found very beautiful: “Beautiful view. Magnificent desolation.” That’s exactly right, I think. Magnificent desolation. Majestic in its blankness, spectacular in its emptiness. A world with everything stripped away except the rock and the light.

They planted the flag — an American flag, though Armstrong was careful in his remarks to say this was for all of humanity, and I believe the intent was indeed for all of humanity even if the flag on the pole is ours. They set up science experiments: a seismometer to measure moonquakes, a corner reflector so Earth-based lasers can measure the Moon’s exact distance. They collected samples — forty-seven and a half pounds of rock, bagged and labeled. Every pound of that rock will be worth more to science than its weight in gold.

President Nixon called them from the Oval Office. He said something about this being the greatest week in the history of the world since the Creation. I found this a bit much. But I understand the impulse. How do you describe this? What language is adequate?

The moonwalk lasted two and a half hours. They came back inside. Sealed the hatch. Repressurized the cabin. They would rest — actually rest this time — before the ascent in the morning.

I sat in my living room after the television coverage wound down. The kids had gone to bed. Betty was dozing. I sat alone for a while.

Two people walked on the Moon tonight. They stood on its surface and looked at Earth hanging in the sky and came back inside and are sleeping now, 240,000 miles from where I’m sitting. The footprints are there in the dust. The flag is there. The equipment is there. Something permanent has happened tonight, something that cannot be undone.

Tomorrow they come home. Tonight, for a few hours, two men are sleeping on the Moon.

I keep thinking that and I can’t quite make it real. Two men are sleeping on the Moon tonight.