Rocking all over the world.

[prso1982]

So I have read a few articles and watched a couple of documentary's about our moon and how it keeps the Earth from rocking. Can any one tell me about the other planets in our solar system? Do any of there moons help stabilize them? What about Venus? It's about the same size as earth and as I know doesn't have any moons. Thoughts please.

 

[yevaud]

I *think* I know what you're asking...

Every large body in our solar system spins. Have you ever whirled around something heavy on a rope, around your head? If you did, did you try to make it change the plane it was revolving in? This is Centripetal Force and Inertia operating together. The body has a natural tendency to remain in that plane, unless some serious force operates to overcome it.

Now this IS a bit superficial, as many planets do indeed "rock," in a regular and predictable fashion. For example, Earth has an axial tilt that runs between 22.1 - 24.5 degrees, each and every year, back and forth.

Here's some reference material for you:

Reference Centripetal Force: http://en.wikipedia.org/wiki/Centripetal
Reference Axial Tilt: http://en.wikipedia.org/wiki/Earth_wobble

Does this help?

(Sorry that's all a bit superficial...kinda on the run today)

 

[MeteorWayne]

Probably because Yev was on the run, he misstated one thing. The earth's obliquity (axial tilt) varies from ~ 22.1 to 24.5 degrees with a period of about 41,000 years. Over the period of a year the change is imperceptable. It is currently 23.44 degrees and decreasing.

It is the top (blue) trace on this chart.

http://en.wikipedia.org/wiki/File:Milan ... dCores.png

Mars on the other hand has a very chaotic obliquity. in the recent past (hundreds of missions of years) from 11 to 49 degrees, but there are hints the range may be even higher than those limits in the more distant past.

MW

 

[prso1982]

Cheers for the info. In one of the documentary's I watched. It says if it were not for our moon that the Earth would rock back and forth violently. Is this true? And if so, does this happen to Venus seeing as it's around the same size as Earth but with no moon?

 

[MeteorWayne]

Yes, the large mass of the moon relative to the earth keeps our system more stable than most.

Regarding Venus, I read a paper about 2 years ago (I think I have it printed out somewhere, the other copy is on my old hard drive, the one smoking over in the corner) that suggests it's current slow backwards rotation is an example of this same process. It's orbitil axis changed so much, that it rolled completely over!

Wayne

 

[yevaud]

Probably because Yev was on the run, he misstated one thing.

Hi. Yeah, I am just getting bavk, and must go right back out again. I did neglect to mention that, true.

Ah, the horror - trying to answer science questions whilst watching the clock.

 

[neilsox]

Rocking all over violently is a serious exaggeration. Without a moon Earth would change inclination perhaps one second of arc per year instead of the present perhaps 8 seconds second of arc per century. Very long term, no moon would be a problem, as the inclination might be as little as zero or as much as 90 degrees, over a period of a billion years or so. Neil