Originally Posted by mib
I was just pointing out that while nearly everyone knows that the seasons are switched between the hemispheres, the actual physical explanation of that is not that trivial.
For instance, why does the axis of the rotation not change with respect to the orbital plane? I think this is a result of some gyroscopic effect, but I am not sure.
Take the Moon, for example. It is phase-locked with the Earth -- we never see "the dark side" (it is not really always dark, of course). Why does not the same thing happen with the Earth with respect to the sun?
Originally Posted by PeteD
What on earth would change it?
actually it does change a bit... you've got 2 variations:
(rotation of the earth's rotation axis around another axis, perpendicular to the ecliptic plane, with a period of ~26000 years)
(short-term 'oscillations' of the earth's rotation axis, the largest component having a period of ~18.6 years)
PS: please note that it might work differently in the flat earth theory.