As my state (Indiana) has removed Astronomy from the curriculum, my school no longer offers it. I have taken AP Physics B and that is my best knowledge provided by the modern school system, so I apologize ahead of time for any low-level or simple questions. I am wanting to know the equations for determining: 1. The velocity of an entity orbiting another (i.e. a planet around a star) 2. The two axis (major and minor) I'm wanting to build a rudimentary PHP program for creating a basic planetary system, so this will help me become one step closer, thank you!