The Ejs Celestial Globe model simulates the Two Sphere Universe theory of the Ancient Greeks. This theory supposes the stars to be fixed on the surface of a Celestial Sphere, with the spherical Earth at the center of this sphere. The simulation shows the motion of Sun and stars in this model, as well as the horizon plane for an observer on the spherical Earth. Two views are shown: one from outside the Celestial Sphere, and the other from the point of view of an observer on Earth looking up. Most of the characteristics of the simulation can be adjusted, including the period of Sun's motion, the tilt of the ecliptic relative to the equator, the latitude of the observer, the time of day and the time of year.
Quelle: Open Source Physics