It seems I am constantly been offended with some mention of the dark side of the Moon. This isn’t an attack on Pink Floyd, because at any given time, there is, in fact, a dark side of the Moon. But in Space: 1999, Moonbase Alpha was located on the dark side of the Moon. Now I understand, Space: 1999 was not in love with science. It was 1 part science and 1999 parts fiction. But it isn’t alone. I see this all the time.

There are many things that lead people to think that there is a dark side of Moon. I think that people mistake the outer side of the Moon with the dark side. But anyone who thinks about it for an instant will realize half the Moon is lit up when we are at the quarter Moon. That means the outer side of the Moon must be similarly half-lit. Just the same, the mistake is easy enough to make with our foggy brains.

The Other Side of the Moon

The Moon is tidally locked with the Earth. That means that the same side of it always faces the earth. Until we started sending rockets out into space, we had no idea what the outer side of the moon looked like. Well, we knew it looked a lot like the inner side. It turns out that because of Moon wobbles, we can actually see 59% of the Moon’s surface. That’s not all at once, of course. We have to watch it for a long time. But it’s easiest to say that half of the Moon can’t be seen from the Earth.

Thus, in a sense, the outer side of the Moon is the “dark side of the Moon.” And it is what we people are getting at when they talk about putting Moonbase Alpha on the dark side of the Moon. But it actually doesn’t make any concrete sense. The Moon is between the the Earth and the sun. Compare this to the new Moon (when the Moon is right between the Earth and the sun). That is: when the Moon is “new” — meaning that the dark side of the Moon is facing the earth. The time when the outer Moon is dark is when the Earth is between the sun and the Moon.

The Dark Side of the Moon Is Constantly Changing

Regardless, the outer side of the Moon has a day just like every other part of the moon (unless you want to get technical and talk about the lunar poles): 27.3 Earth days. I think, however, that Pink Floyd is responsible for this error of thought in the song “Brain Damage.” That’s not to say that they were thinking wrong. Waters is a great lover of metaphor. And the song doesn’t even imply that the dark side of the Moon is any particular place.

But people have picked up on it. And “dark side of the Moon” sounds better than “outer side of the Moon.” Although actually, from a metaphorical standpoint “outer” is probably better than “dark” given that we can actually see a great deal of detail in the dark side of the Moon. It is the outer side that we can’t connect with.

The Moon Is Fascinating — We Should Understand It

Regardless, I bristle every time I hear the term used because I know that it is a sign that people are not understanding how the Earth and Moon interact with each other. And this is important to me because learning what caused the phases of the Moon was really important to me. Plus, as I learned when I taught planetary astronomy at college, people really don’t understand this stuff. And it’s so easy and so cool. If there really were a dark side of the Moon, that would be hard to understand.