Moon Mysteries questions....

[vonmazur]

Recently, on Science Channel, there was a program about the moon. The promulgators stated that if there our moon was gone, the Earth would be unstable. OK, what am I missing from this idea?? Venus is the size of Earth and has no moon, does it wobble and flip over, like these guys claimed??

What is the moment or force that would cause this? Water(Oceans) Ice caps??

TIA....

Dale

[dgavin]

Well it's a bit more complicated then just a moon required for stability.

Venus is odd in that it rotates slowly and in opposite direction of all the other planets. It's also odd in that its axis of rotation, doesn't also rotate.

The earth's axis of rotation also rotates, about once every 26000 years. This leads to the precession of the Equinox used in many calculations (including probably being the basis of the Mayan calendar that was on a 26000 year cycle also)

Without the presence of the moon, or without earth being a moon of a larger planet, the double rotation would be unstable.

A Spinning top is a good way to see how a single axis spin in stable, and double axis rotation is unstable.

Hope that explains it a bit better

[grant hutchison]

The suggestion, I think, is that the Moon's gravity is the dominant influence on variations in the Earth's axial tilt. Under the strong but pretty constant influence of the Moon, the Earth's rotation axis precesses quite rapidly, and wobbles in a relatively minor way as a result of cycles in the Moon's orbit. So the Moon effectively "drowns out" lesser gravitational influences, leaving them as no more than a little noise in the precessional behaviour of the Earth.

In contrast, Mars is subjected to just the weaker but highly variable perturbations from its planetary neighbours, and so precesses slowly but with wide and chaotic variability in its axial tilt (anything up to 60&#186.
IIRC, simulations have shown that in the absence of the Moon, the Earth would experience similar slow but major axial wobbles.

So the fast precession induced by the Moon is protecting the Earth from getting into the sort of chaotic behaviour that affects Mars.

Grant Hutchison

[vonmazur]

Thanks, I was wondering why they did not get into the precession, just the statement and then they went on to something else...

Dale