Celestia Forums

just wondering if anyone know if the earth's tilt has anything to do with the wobble.

Frosita

The Earth doesn't really "wobble" in the conventional sense. It does, over very long periods of time, change its tilt angle. This is called "precession" but it is a long term process.

And that woble has another profound effect. It changes our pole star. Polaris the north star insn't going to be our pole star for much longer in the sceme of earth's history. I can't remember how long it takes but its several thousand years and the north pole will the be pointing at another star instead. The woble is really nothing in the big picture. Now what I am waiting for is the polar magnetic reversal. If it were to start in lets say the next couple of years all hell could break loose. Many of out satalites won't have the protection of the magnetic field and they don't have that kind of shielding built in and of course niether do we. We would probably loose power grids all over the earth. Telecomunications would go down, hence say goodby to the internet and many geopolitical upheavals would shurly follow. I just love doomsday. There are just so many diferent kinds of doomsdays. Anyone up for sub-atomic particle sanbathing. We will defenetly need the 1000 power sunblock to outside in the daytime. One plus will be there will beautiful auroras all night long. Just something for everybody to ponder.

Frosita wrote:just wondering if anyone know if the earth's tilt has anything to do with the wobble.

The "wobble" you've been talking about on another thread is called precession, and it does occur because the Earth's rotation axis is tilted relative to the plane of its orbit. It arises from the same mechanism as the twirling of a tilted gyroscope. In the case of a gyroscope, its tilt relative to the floor stays the same, but its axis of rotation twists parallel to the floor in the same direction as the gyroscope is spinning. In the case of the Earth, the tilt relative to the plane of its orbit stays the same, but the axis twists in the opposite direction to the Earth's rotation - taking about 26 000 years to go around once. The difference in precession direction between a gyroscope and the Earth is because gravity is trying to increase the tilt of the gyroscope (ie: it's falling over ), whereas the gravity of the Sun (and Moon) is trying to decrease the tilt of the Earth - pulling its equator into line with its orbital plane.
Superimposed on the grand slow turning of precession there are other motions that might better be called "wobbles" - a complex 19-year oscillation due to the varying positions of the Moon, called nutation; a fourteen-month oscillation called the Chandler wobble, arising because the Earth is not a perfectly uniform shape and density; and a yearly wobble induced by the seasonal shifts of atmosphere and water.

Grant

Thanks for the info. now I know we have 2 axis one for the tilt and one for the long term wobble. oh and probably some more for the other wobbles. Does this mean that if our moon went caput we would just start flipping over and over or is it mainly the sun that is pulling us back into line.

cheers

frosita not logged in wrote:Does this mean that if our moon went caput we would just start flipping over and over or is it mainly the sun that is pulling us back into line.

In the short term (<1 000 year), the precession rate would slow and most of the nutation would disappear, because the force of the Moon's gravity is making a very significant contribution to both of those effects. In the longer term (>1 000 000 years), my understanding is that the Moon actually has a stabilizing effect on the more chaotic motions of the Earth's axis - so we would see more climatic extremes as the Earth's tilt varied between wider limits.

Grant