Warning: the performance of this simulation may vary from one system to another. Please see the "Use Transparency While Running" option in the Display Options Menu of the Globe Frame below for information on how to achieve the best performance on your computer.


EquinoxPrecession


General Description

This program illustrates Copernicus' theory of the precession of the equinoxes. As Earth orbits Sun, Earth's rotational axis precesses about the axis of its orbit (the ecliptic axis). This simulation shows three different views of this effect. One view is from outside of the Celestial Sphere, showing the motion of Earth along its orbit as well as the precession of its rotational axis. This view also shows the celestial equator and the ecliptic. The intersection points of these two circles are the equinoxes, and the program illustrates how these points move through the stars as Earth's rotational axis changes direction. The second view shows the sky seen by an observer at a location near Earth (but not ON Earth) and with one of the ecliptic poles at the zenith. This view shows the rotation of the celestial poles and the equinox/solstice points about the ecliptic poles. The third view shows a strip of sky in the vicinity of the ecliptic as seen by an observer on Earth. This shows the motion of the sun along the ecliptic as well as the motion of the equinox/solstice points due to precession.

Note: in all three views the daily rotation of Earth has been neglected. One good way to think about this simulation is to imagine that the animation is shown in steps of one sidereal day (so that Earth has undergone a complete rotation and returned to its original rotational position after each step).


Globe Frame