Analemma
Gallery:
Site Images The obliquity of the Earth's orbit raises and lowers the height of the analemma (i.e., the height of the figure eight) in 40K year cycles (20K rising, 20K falling). Glacial epochs over geologic history have often occurred within a few thousand years after the analemma drops to its lowest height in the Northern Hemisphere (analogous to the one-two month delay in the coldest part of winter after the autumnal equinox). Of course it's never that simple. See here.
