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.

EJS Equinox Precession model was created using the Easy Java Simulations (EJS) modeling tool.  It is distributed as a ready-to-run (compiled) Java archive.   Double clicking the ejs_astronomy_EquinoxPrecession.jar file will run the program if  Java is installed.  EJS is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models.  Additional EJS models for astronomy are available.  They can be found by searching ComPADRE for  Open Source Physics, OSP, or EJS.

Please note that this resource requires at least version 1.5 of Java (JRE).