Is Earth's axis really tilted?

Strange Question? Of course, it is. Well, umm, actually it depends on your point of view. Usually, we think of the ecliptic (earth's orbital) plane as the horizontal plane. If we do so, earth is actually tilted towards it. This view can be seen in the animation below.

However, we may change our point of view. If we think of the earth's equatorial plane as the horizontal plane, then things look a bit different. In that case, the sun is tilted against earth. An orbit plot looks a bit different now:

The underlying physics is all the same - just the angle we are looking at it is different. No matter how we look at it, the fact remains that there is a tilt of (currently 23.44 degrees) between earth rotational axis and the ecliptical plane. And this tilt is quite important, as it causes seasons on earth.

Just a remark to the animations: these were created with the astronomy software RedShift 6. The animations are not to scale. I have greatly zoomed earth, so that some details can be seen. If you look closely, you can also see that the equator and the ecliptical plane cross each other only twice a year - at the equinoxes.

Copyright © 2007 Rainer Gerhards
Animation: Rainer Gerhards
Last Update: 2007-06-21