The EJS Equinox Precession model illustrates the Copernican theory of Earth's orbit around the sun. The top window shows a view from outside the celestial sphere. The simulation shows the moving Earth along with its axis or rotation and the line of sight from Earth, through Sun, to the Celestial Sphere. The end of the arrow indicates where, on the Celestial Sphere, Sun appears to be located as seen from Earth. The tilt of Earth's rotational axis (relative to the ecliptic plane) is adjustable. The bottom window shows the view of a portion of the sky (near the ecliptic) as seen by an observer on Earth. You can modify this simulation if you have EJS installed by right-clicking within the plot and selecting "Open Ejs Model" from the pop-up menu item.
Quelle: Open Source Physics