Why doesn't the Moon get a cool name?

04 February 2020

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Question

Why doesn't the Moon get a cool name like the others?

Answer

We put this space question to astronomer Matt Bothwell...

Matt - I love this question so much. It's such a good question. You're absolutely right, the moon, we're so used to it as a name. It feels very boring, right? Compared to the lovely and evocative names from the rest of solar system. You mentioned Phobos and Deimos and yeah, some moons have Shakespearian names like Oberon, all these kinds of things. The answer really is that we've known about our own moon for a very, very long time. Almost to the point where it's hard to say that the moon was discovered, right? I mean all you have to do is look up and it's, it's there half the time. So we've, we've known about the moon through all of human history really. All the other moons in the solar system are very, very tiny and need telescopes to be able to see them. And telescopes didn't come on until a few hundred years ago. So the moon was named thousands and thousands of years ago. Our word moon actually comes from the name month because the moon takes one month to go on one orbit, one trip around the earth. So that's where the word moon comes from.

Chris - Because the lunar cycle when it goes full moon and then into a waning moon when it goes in three quarters, quarter, back to invisible again.

Matt - Right, exactly. And that was a way that they used to measure time. The reason the word measure and moon sound similar is because the original word that gave the root of moon is the same as the root of the word measure. Because it was the original measurement -

Chris - And menstruation as well, isn't it? Because they actually said that's the 28 day cycle, which is roughly the same. Just by chance, I understand. Nothing to do with the moon, but that was also a 28 day cycle. So people said, "well, it's something to do with the moon. Must be, right? It's the same length of time." And so it got the same name.

Matt - Other languages also have very nice and evocative names for the moon as well. So we say moon in English, but in Latin they say luna for example.

Sam - So Matt, you've reminded me of a question I've had about the moon for a long time. And I'm sorry if I put you on the spot here. Is it just coincidence that the same side of the moon always faces us or is there some funky physics at play?

Matt - The answer is very much funky physics. The reason the same side of the moon faces us all the time, it's not actually because the moon doesn't rotate, cause it does. It's that the moon's, how long it takes the moon to spin on its axis is exactly the same as how long it takes for the moon to go on one orbit around the earth. That's a process called tidal locking. So when you have two bodies that are quite close to each other in space, uh, the, the rotation periods and the orbital periods get synced up in this way.

Chris - One other question - Sam's got me thinking now - someone asked me the other day, "when we have an eclipse and you have a total eclipse, is it just fluke that the moon is just the right size to completely cover the sun the way that it does in our particular neck of the solar system?

Matt - So the answer to that one is just fluke. Yes. In fact, in the future, that won't be true. The moon is actually traveling away from the earth by about a centimeter per year. And so if you go to, maybe 500 million years or a billion years in the future, the moon will be too small, and actually we won't get eclipses anymore.

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