Motion of planet in an ellipse around the sun.

The planet moves in an ellipse, with the sun at one focus.[br]The area swept remains constant.[br][br]Investigate moving the second focus (B) and the point of perihelion to discover the how the planet moves.[br]Look at the code to see how Kepler's equation is solved numerically.

In Euclidean geometry, the angel bisectors of a triangle are concurrent at the INCENTER, which is the center of the inscribed circle. In the sketch below, the same construction is carried out on a spherical triangle. Point Q is the incenter. The green circle is the incircle.[br][br]Drag points A, B, and C around slowly. The construction responds somewhat slowly...there are quite a few great and small circles constructed.