Tonight, shortly after midnight, the sun may be said to stop on its northward travel, hesitate a moment (hence the meaning of solstice – “sun stop”) and start its return journey south, where it will be headed for the next six months. Well, that’s the way it looks from here. But if you believe, as Copernicus did, that the sun rather than the earth is at the center of the universe, you might think the earth is wobbling back and forth causing the apparent back and forth travel of the sun. Happily for us, it is not wobbling much. (By the way, though I don’t fault him, Copernicus was wrong. There is no center. Wherever you are, nearly all of the universe, excepting only nearby stuff, is rushing away from you in the aftermath of the big bang, so you are as much at the center of the universe and anyone else.)
When the earth was formed, its axis was perpendicular to the plane of the sun’s orbit (and the plane of the sun’s equator) and was without seasons. The earth then famously collided with a Mars-like object only a few million years after the solar system was formed, knocking us sideways, giving us seasons, and forming our critically important moon.
The earth spins pretty consistently, although slowing gradually over time, and to our great good fortune, it spins around an at an angle of approximately 23.4 degree relative to the plane of the sun’s equator. Thanks to the moon’s stabilizing effect (unique in this solar system) this angle is pretty steady. If there were no such angle, there would be no solstice, no seasons, and much larger parts of the earth would be far too hot or too cold to be habitable. Also, without the stabilizing effect of the moon, the angle of the earth’s axis would not be consistent, and the sun would shine all over the place, appearing to move from time to time almost directly above the north and south poles, variously scalding and freezing most of the earth and making it unlikely that large life forms would have developed on this planet.
A final note — the earth does wobble a little, up to about 1.3 degrees; it is one of the reasons for ice ages and extended periods of warming. But these wobbles are slow and are not related to the climate changes created by the billions of us turning long buried plants and animals into gasses that our oceans and plants are not able to metabolize at a rate sufficient to keep things the way they were.
Yours from the field,