What will happen to Earth as our Moon moves further away?

Question

In a NASA article 'Eclipse Predictions and Earth's Rotation' it states that "The Moon's average distance from Earth is increasing by 3.8 centimetres per year."

I've not heard anything about this before, but knowing a little about how vital our Moon is to our planet it does concern me somewhat, and I'd like to know...

1. Why is the moon moving further away?
2. What effects will this have upon the Earth as our Moon gets further away from us - i.e. on tides, etc?
3. How long will it be before we notice the effects on the Earth of our Moon being further away from the planet?
4. How far away will our Moon go, and what will happen to it/us then?

Thank you.

Just because changes may not happen in my lifetime doesn't mean I still can't be concerned, or curious about this.

DO ANY ASTRONOMERS USE THIS SITE?? WHY ANSWER WHEN YOU HAVE NO CLUE??

Answer 1

1. The moon is moving further away because of a complex gravitational interaction with the earth. Briefly:
* The gravity of the moon creates "bulges" in the earth's oceans. Normally those bulges would point directly toward and away from the moon, BUT...
* The spinning earth "drags" the bulges a little toward the east (due to friction). This means the bulges don't exactly line up with the direction the moon is in.
* This affects gravity. If everything were perfectly symmetrical (no off-center bulges), the moon would feel a pull directed exactly toward the earth's center, which would result in a perfect elliptical orbit. HOWEVER...
* Because the ocean bulges are a little "off-center," the earth's gravity does not pull "straight down" on the moon, but instead pull mostly down and a little sideways (toward the east).
* This small "sideways" tug on the moon causes it to spin out into a wider orbit, kind of like when you smack a tetherball sideways. (Except there's no rope to wind the moon up :-)

Well, that's about as brief as I could make it. :-)

2. Effects on the earth:
* The earth's rotation will slow down (IS slowing down). This is a side effect of the friction that happens as the earth "drags" the tides eastward (see above). It's also predicted by the law of conservation of angular momentum--you can say that this earth/moon interaction is "transferring" angular momentum away from the earth an into the moon.
* ALL ELSE BEING EQUAL, the average height of the tides will gradually diminish. But in fact, the size of the tides is also affected by things like global climate (which affects how much land ice there is, which affects the sea level, which affects the shape of the coastline, etc.). Those things change on a much faster time scale than the receding moon; so THEIR effect on the tides (whether it makes them bigger or smaller) is likely to dwarf any effect caused by the moon receding.

3. This is hard to answer. The most noticeable effect is the slowing of the earth's rotation. Although this is MEASURABLE today, it certainly doesn't affect people's everyday lives. If the earth continues to slow down at its current rate, then in about 50,000 years the length of a day will be about 1 second longer than it is now. So we may decide (in the year 52,000 AD) that we ought to add a "leap second" every day at midnight in order to keep our clocks accurate. That's probably the biggest cultural effect that it'll have.

4. At its current rate of recession, the moon will recede about 100,000 miles over the next 4.5 billion years (making it about 43% farther away than it is now). But in fact the rate of recession will gradually decrease over the years, so it will not really get quite as far away as that. And at that time, it's expected that the earth & moon will be swallowed by the sun as it turns into a red giant--so we'll have other things to worry about!

Answer 2

The Moon is NOT being pulled further away by the Sun's gravity. Think about it: the Moon and the Earth are at about the same distance from the Sun, with tiny monthly variations. The Sun IS pulling the Moon, but it's also pulling the Earth with very nearly the same force per kilogram. That means that the centripetal acceleration of the Moon is the same as the centripetal acceleration of the Earth, and one isn't moving toward the Sun faster than the other. Besides, if that were the explanation, you would expect to see the Moon's orbit becoming more elongated toward the Sun. But the Earth-Moon distance is growing all around the Moon's orbit, so there must be another factor at work. The Moon causes a tidal bulge in Earth's oceans, meaning that water facing toward and away from the Moon is stretched out a bit. The effect isn't much, compared to the diameter of the Earth, but it's real. If the Earth were not rotating, the tidal bulge would line up perfectly with the Earth-Moon line. However, the Earth IS rotating, and it sweeps the tidal bulge forward a tiny bit. Because the mass of the tidal bulge is "ahead" of the Moon, it causes the Moon to accelerate in its orbit. A higher orbital speed means a larger orbit, and so every century the Moon moves a little bit further out due to tide-induced acceleration. Of course, kinetic energy can't just be created like that. As the Moon gains kinetic energy, it robs it from the Earth. Due to the Earth's tidal interaction with the Moon, the Earth's day is also slowly getting longer. We won't see any noticible change in our lifetimes, but in a few million years we'll have to invent new clocks if we're still around as a species.

Answer 3

I read something about this years ago, but because things like this are written in a scientific language only some of it sticks. I just tried to explain it, but on re reading it realised it was crap so deleted it. I may have told you (can't remember) i once saw a documentary called 'The day earth began' it started off with the moon and earth as big rocks colliding and then from then on how the earth evolved to how it is now on computer models over a 24 hour clock, it was in simple engish so really easy to understand and very interesting,. You can't get it on DVD yet I've been looking for 3 years but it is played on the discovery channel now and again. I think i recently read that without a moon we would have severe wind. I am so sorry about crap vague answer. I can tell you it has something to do with the collision of moon and earth 4.5 billion years ago.
Firestarter - that is total Boll0cks.

Answer 4

For the DVD talked about in the answer above. The Program is part of "THE UNIVERSE" on Discovery Channel. There is a whole set available. I own them on dvd, very good series. Explains all the little questions like this one that someone might have on any planet in our Solar System.

Answer 5

Al Gore says that we of the earth have caused the Moon to want to move away it 's the pollution we have left there is causing lunar shifting as scary as global warming and just as much our fault

Answer 6

This distance increase will not cause any noticeable changes for a longer period of time than you can mentally grasp.

Answer 7

Whether you believe me or not I don't care. But you don't have to panic because everything is under control.

Answer 8

Hmm...interesting lol

380cm further away in the average persons lifetime of 100 years - GOOD GOD WE'RE DOOMED, DOOMED I TELLS YA MR. MAINWARING!

How far is that in terms of metres, miles, lightyears? NOT ENOUGH TO BE SHITTING YOURSELF ABOUT REALLY IS IT?

Answer 9

i can't imagine it will move out for ever but perhaps its just reaching an equilibrium distance away.

Answer 10

tides get weaker - gravity gets stronger - we won't live long enough to experience this so stop worrying