If I've done this right, this post will appear at 20 July at 20:17 UTC -- 40 years to the moment from when a manned spacecraft from Earth first touched down on the surface of another world.
I was 12 years old and my family was on vacation, camping at Rocky Mountain National Park in Colorado, right up by the continental divide. We had been into town for something -- I don't recall what, maybe a restaurant dinner; I don't even recall which town -- and on our return in the evening, stopped at a little country store to pick up whatever. I stayed in the car while my parents went inside.
A few moments later my Dad re-emerged, beckoning frantically at me to come inside. In the store, I found a crowd of people gathered around a dutch door at the back that gave into the owner's living quarters. The upper half was open, and everyone was watching a small black-and-white TV perched on the kitchen counter. On that screen was Neil Armstrong taking his first few steps on the moon. Not that I could see much: by the time the low-bandwidth lunar signal had been received, converted to broadcast format (by pointing a TV camera at the slow-scan monitor in Mission Control!), been broadcast by the networks, filtered through the local weather (as I recall it was raining, maybe even thundering) and made its way to the rabbit ears of this little receiver way up in the Rockies, all that was left was a bunch of monochrome blobs that moved every so often.
Back at camp, I fell asleep in our tent trailer that night listening to the radio coverage. Before turning in I made a last visit to the washroom. At our altitude it was pretty cold for July; but the weather had cleared and the sky was crystal clear as only a high mountain sky, far from any city, can be. The moon was full and dazzlingly bright in my memory.
And a 12 year old boy looked up and realized: that's not just a light in the sky. It's a world -- and there is a man walking on it!