The moon orbits the earth once every 29.5 days. That is why there are about 29 days between full moons. About once a month, the moon’s phase shifts from full to waning to new to waxing and back again. In fact, that’s where the word “month” comes from, from an Old English word mena, meaning “moon.”
What’s also interesting is that the moon also takes 29.5 days to rotate on its axis. It takes the exact same amount of time to rotate as it does to revolve around the earth. This means that the same side of the moon is always facing the earth. This phenomenon is known as tidal lock or synchronous rotation. This is the reason that the full moon always appears exactly the same, the reason why the “Man in the Moon” is always there doing his thing. This is not uncommon among planets and their satellites, but it’s a good thing that the earth and the sun aren’t tidally locked, or there wouldn’t be day and night — one half of the earth would always face the sun, and be baked to a crisp, while the other side would always face away, and be frozen solid!
This is why people talk about the “dark side of the moon.” There is a side of the moon that nobody on earth has ever, ever seen. (Except for a few astronauts who have orbited the moon.) But interestingly, it’s not actually any darker than the rest of the moon. That side of the moon sees the sun just as often as the “light side.” When we look up at the moon and see only a crescent or a half moon, that means that part of the “dark side” is actually facing the sun. So the so-called dark side of the moon is more accurately called the “far side of the moon,” because it really is always on the side facing away from the earth. Any moon-beings who might live on that side of the moon would never, ever see the earth in their sky; as far as they’re concerned, the earth might not even exist. Weird!
And that makes China’s recent moon landing very intriguing and important. Every landing that the United States made on the moon back in the 1960s and ’70s was made on the near side of the moon, the side facing the earth. This was just common-sense, because you can’t send messages from earth to the far side. (There’s something really big and massive that blocks them — the moon itself.) There would be no way to be in contact with Houston if they landed over there. But technology has moved on a bit since then, and China put a satellite in orbit around the moon a few months ago, which acts as a relay between their lander craft and earth. So we’re right now getting our very first pictures of the surface of the far side of the moon — ever. (NASA had done some photography and mapping during the Apollo program, from orbit, but this is from the surface. Quite different!)
It’s so exciting that China is working so hard at space right now. They’re trying to overtake us, and I think that’s awesome, because the Chang’e lander that landed a few weeks ago is the first craft to land on the moon in my 43-year lifetime. (Well, not exactly. There have been a few Chang’e landings in the past few years. But this is the one that got all the publicity, because of the “far side”.) I guess this is what happens when a nation enters into a rivalry with the United States. The last rival we had was the Soviet Union, and the Cold War was pretty much the whole reason behind all the money put into NASA, and into the USSR’s space program. Now China has something to prove, and they’re heading to space to do it. I think that’s great — if it takes a global pissing contest to get us some more space travel, then bring it on. The more space, the better.