Half a century ago today, humans first set foot on another world - our companion, the Moon. For thousands of years we had looked up at the sky and seen the
Moon - the only one, nothing else like it in the sky, except maybe the Sun that seemed to be its partner. We now know that the Sun contains almost all the mass of the whole Solar System. Everything else shares a fraction of 1% of the total mass. But the Moon looks the same size as the Sun from Earth. As it happens, the disk of Sun is about 400 times bigger than that of the Moon, but is 400 times further away.
It was quite a shock when Galileo discovered that Jupiter had four
moons. (It has actually has loads more than that, but you can't see the others with a small telescope.) It took less than three centuries after that to realize everybody had moons except Mercury and Venus. And it didn't take another century after that before 12 people had walked on the Moon and another 12 had orbited it.
I liked Michael Collins's account of Apollo, written without a co-author or ghostwriter.
What was it like to be one-third of the Apollo 11 crew? Michael Collins, the man in the command module that didn't land on the Moon, tells a fascinating story of astronaut training and space travel. Carrying the Fire - Book Review