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Earth is at an angle to the sun which gives our seasons and is an easy one to observe in action.

But whey is it there?

Why is the wobble due to precession there?

Why does the moon orbit the earth on its plane?

Does the angle the moon orbit change with precession? or is that in a fixed plane?

Is there an interrelation between all these?

Edited by Earl
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I thought the Earth's tilt was thought to be due to early collisions with other objects as it formed. Maybe even the collision with the large object that is thought to have produced the Moon itself.

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I think you will find that most (all) spinning objects precess.

Try a simple wind up kids spinning top or one of those gyroscopes you could/can buy.

Recall at O-level physics it was a question that you had to work out, in effect there is always precession and you had to work out how much. If it were not a constant property then you could not work out how much is present as there could be anything between lots and none and indeterminate.

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humm does this say the the circle of precession over the duration of a full rotation is a bit larger after the period of one rotation?

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There's an idealized situation and a real situation. In a real one things get a bit knocked about.

The sun formed from a collapsing cloud of gas and dusty bits and bobs.

The conservation of angular momentum wound up the collapsing cloud into a spinning ball (the sun) and a spinning disk of stuff around it which would form the present solar system. The angles of spin would be in close agreement between sun and disk. There's a difference between close and perfect. WIthin the disk things began to self-gravitate together, colliding and combining to form spinning blobs with a fair memory of their original plane of ratation but, hey, they are colliding! They get a bit kicked out of kilter and pick up a bit of tilt here and there.

A perfectly balanced spinning object would, you might think, spin without precessing or nutating. If you thought that then you would also think that it would be possible to balance a pencil on its point. But you know full well that a pencil cannot be balanced on its point and never will be. I've read that chaos theory can give a proof of this but that would be way outside my competence to discuss further. Read Gleick's book on Chaos Theory if you're intrigued. 

So given all the banging about that was going on during the formation of the solar system (as demonstrated by the less than glossy smooth surface of the moon) I think that the spinning bodies we now see have done a remarkably good job of retainaing a memory of that protoplanetary disk... Hey, c'mon, how neat and tidy is Saturn??

Olly

Edited by ollypenrice
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Earth is at an angle to the sun which gives our seasons and is an easy one to observe in action.

But why is it there?

One could ask what is the chance that there would be no orbital tilt? Random changes in the early solar system will have moved everything away from an ideallised situation.

Why is the wobble due to precession there?

Observe a spinning top in action. It will be inherently stable because of it's spin but that axis about which it spins will move. The Earth (and all planets) just do the same on a grander scale. In detail it comes down to mechanics. Objects are only stabilised by spinning but there is more than one axis around which stabilisation is required. The major component is the planetary spin (left over from the collapse of the spinning protoplanetary disk), the minor component is the precession (left over from the collapse transverse to that which is a much smaller angular momentum)

Why does the moon orbit the earth on its plane?

As the early solar system collapsed it would have formed into a disk. That is a positive feedback process once started so most solar system objects orbit within the same plane.

Does the angle the moon orbit change with precession? or is that in a fixed plane?

No. Precession affects the orientation of a spinning objects axis but not the inclination of that axis.

Is there an interrelation between all these?

Most of these effects arise from the early solar system collapsing as a disk which means that everything is align in a plane so yes there is an interrelation, or more accurately a common cause. Of course the universe is a messy place so that's not exact and things deviate slightly from that.

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