So a year or so ago I had a different blog which occasionally tackled science-type topics, it was… not a success. But, one of those posts was this one, which I thought I might as well share so there’s something here over the long weekend.
This post isn’t really Mars related – but it is about the Moon, and us being on it, and how the Moon is trying to kill us by escaping.
That’s right… The Moon is escaping, and we’re all gonna die!
Over-reaction? Possibly. But is it true? Well, to a certain extent, yes.
When Apollo 11 said goodbye to the Moon in July of 1969, they left something behind. Well, they left a number of things behind, but among the things they left behind were some corner-reflectors, which is what we’ll focus on.
There’s a picture of a corner-reflector on the Moon. Suck it, nerds. Moving along…
These corner-reflectors are special apparatus which allow laser beams on Earth to be aimed at the Moon’s surface. Those beams are then reflected precisely within the reflectors and return precisely back to their original source. Why? Well, first off it proves that mankind did walk on the Moon – so it shuts up conspiracy theorists, but also – it allows us to carefully measure the movement of the Moon.
That’s how we confirmed that the Moon is, in fact, getting farther and farther away from the Earth.
Yes, that’s right. The Moon is running away. And the Earth is to blame.
At a rate of about 3.8 cm a year – the Moon is moving away from the Earth, and it’s been doing that since day one, which in the Moon’s case was around 2.3 billion years ago (give or take a billion). That’s about the time we got our moon – and we’ve been losing it ever since. Like a horribly co-dependant high-school romance, the Earth and the Moon have been inexorably joined and inevitably breaking up since the day they got together – and it’s all because of the Tides.
Now then, in order to explain why the Moon is escaping, we’re going to be getting into some rather complicated physics and science and whatever. Let me be clear that I am horrible at math, I hate equations, and I’m not at all good at physics in general – but I like to understand things, so we’ll work through this together.
There are three bodies in this tale of abandonment; the Earth, the Moon, and the Tides. I know the Tides (capitalized to foreshadow their importance) are technically a part of the Earth, and in truth the Moon is part of the Earth as well – and that’s the point sort of – the Earth, the Moon, and the Tides are all part of the same rotational system. You can think of them as being linked, joined in a partnership, in a careful balance that always has to even out. That balance is part of something called ‘angular momentum’ – which I’m going to try to avoid talking about.
Back to why the Moon is escaping.
As the Moon orbits the Earth, it pulls on the Tides and the Earth as well – this we know… seas rise and a bulge forms along the surface of the Earth. This happens because of gravity – because the Moon is close enough and massive enough to have a profound effect on our planet. But, just as the Moon affects the Tides, the Tides affect the Moon.
As the Tides bulge on the surface of the Earth, they create friction with the Earth’s surface, which is rotating quickly under the bulge, and dragging it with the Earth. This causes the Earth to slow down fractionally (I’ll come back to this – but let’s stay on track) – but in the tug of war between the Tides and the Earth, the Earth wins – it drags the Tides with it, and out of alignment with the Moon.
Now, the Moon is just as gravitationally attracted to that tidal bulge – so because the friction with the Earth drags the bulge ahead of the Moon, the Moon speeds up – pulled a tiny bit faster by the gravitational mass of the tidal bulge. Rotational energy is in effect drawn out of the Earth and transferred to the Moon. This causes the Moon to speed up just a bit – and as we all should know, when something in rotation speeds up – it moves out (this digs into angular momentum, which I don’t need to get into – because I don’t quite understand it). Think about a weight on a string, as you spin it around faster and faster, it pulls away from the centre of its rotation… right? Either way, we’re moving on – the Moon is speeding up, slowly, and as a result – it’s pulling away.
Here’s a picture I found which might, just might, help you work this crap out.
Probably should have opened with that, I guess.
Anyway – Because we are locked in a rotational system with the Moon, if it speeds up – we must be slowing down… which we are. The Earth is getting slower, slowly. In fact, 620 million years ago a day on Earth was 21 hours long… now we’re at 24, and that number is going up by 1.7 milliseconds every 100 years. So those Victorians can suck it, because I get way more shit done in a day than they did. I also don’t have as much Typhoid.
So okay, the Moon is inching away from us. “Big whoop”, as the kids are so fond of saying in 1989.
Well it is a big whoop, smart ass. We need the Moon, and we have always needed the Moon.
Based on best estimates and guesses and calculations, the Moon has been with us for a few billion years (how it was created is still up for debate) – and from the moment it showed up, life on Earth got a whole lot better. The Moon provides a stabilizing effect on the Earth’s rotation – without it we’d wobble about like that dying top at the end of Inception. It steadies our weather and climate patterns. Tidal influence provides a time table for animal spawning – which gives us coral reefs and the like. It keeps us geologically active. It helps animals navigate. And, most importantly, it’s damn pretty.
So with the Moon giving us all that – won’t we be up shit creek when it finally does escape? Well, not really – for two reasons.
1) It won’t literally escape. Eventually the Moon will slow us down enough that we become synchronous, the moon will just stay in the same spot in the sky, and the tides will stop and our day will be something like 47 hours long (or 47 days… I can’t remember), and the Moon will be so far away that we’ll hardly remember what it looked like. But, and here’s the thing of it, the Moon won’t ever escape – it’ll just get farther and farther away.
2) Oh, and the second reason the Moon won’t escape is that by the time any of this starts to actually matter enough to affect us – the Sun will be dying and expanding out to consume the Earth and burn all life on our planet and murder everything everywhere – including the Moon.
So, you can stop worrying. The Moon isn’t going to kill us – because the Sun will do it first.
Assuming we don’t beat them both to it. SCIENCE!