If the moon did not exist

Ulysees

There's a documentary with this title, haven't seen it yet but would like to see it. The premise of the film is, among others, that the earth's axis would wobble (therefore unstable seasons) causing many other things to happen if the moon did not exist, but it does not seem obvious to me at all.

Why would the axis wobble? It wobbles already for sure, giving rise to the Age of the pisces and the Age of aquarius etc as the axis passes through constellations. But why would the moon make a difference?

Any dynamic simulation of this effect? Any youtube video or software to demonstrate it?

D H

If that is an effect, it is a minor one. From http://www.astrosociety.org/educatio...tnl/33/33.html (third page), the primary effects of an Earth sans the Moon would be

1. The day would be eight hours long.
2. The winds would be much stronger.
3. Complex life might not exist yet.
4. When life did arrive, it would have a different biology.

Ulysees

So no mention of the axis changing? The claim that the axis is kept fixed by the moon is false?

mgb_phys

It's a difficult thing to be sure about - surprisingly it's very hard to model what looks like very simple classical mechanics!
The moon will definately have an effect on the Earth's rotation but quite how much the precession would be without it I'm not sure.

There are also theories that it swept up elements from the early atmosphere and sheilds the earth from meteors which would also have a big effect on life.

Noone

didnt the earth effect the rotation of the moon as it slowly got farther away,then finaly the moon no longer has a rotation?

Noone

so if it did, couldnt you say that the moon effected the rotation of the earth in some way? maybe a slower rotational speed? but began faster as the moon moved away in after time?

Noone

Yes it would, there are alot of effects that would take place that would range from mild to extreme, Make's me wonder what would happen if somthing big hit the moon and alterd its path and tilt.

Ulysees

Is it possible that something else also slows down the earth's self-rotation? Like the solar wind?

mgb_phys

Nope - you need something that can transfer momentum ( and quite a lot of it)
Tidal friction with the sun would eventually slow the Earht's rotation (as it has for mercury) but the effect is smaller because of the distance to the sun and so it would take longer to slow us down.

gtrmaster2000

well if the moon did not exist the tides would be very minimal do to the fact that the sun still has its affects. the lunar bulge affect on the earth would no longer exists therefore there would be 2 bulges left instead of the standard 4 that we are used to.

gtrmaster2000

there should be no inflictions of the rotation velocity. well not that i can see. the moon does not add momentum but i understand the bobbling affect. can u explain its momentum given off please? i am in the dark on the subject of momentum

Ulysees

How much do you think? In other words, how much torque is required to slow the self-rotation of the earth from an 8-hour day to a 24-hour day over 4.000.000.000 years?

That's a change of about 1 second per 70000 years. Maybe the necessary torque for this is comparable to the torque exerted by the solar wind as it is diverted by the Van Allen belts!

Ulysees

In fact I suspect they have forced the moon's tidal effect to match the observed change in the self-rotation of the earth. In other words, if the corral reefs showed a day duration of 12 hours instead of 8 hours at a given time, then they would still say the change from then to now was caused by the moon.