Total Orbital Energy
The total orbital energy in a gravitational bound system is a constant. It will be the same calculated at aphelio as well as perihelium. The total energy will be equal to 1/2 <U> the time-average potential energy of the system. The symbol < > is an indication for the average over one orbital period. It is a result of the Virial Theorem. I will be glad to include in the lectures a demonstration for the Virial Theorem if there is a student interested in it. Contact me, and I will be glad to include a demonstration of the Virial Theorem.
The following video is the lecture for the Total Orbital Energy.
http://www.showme.com/sh?h=zvGW4Fk
AstroDidactics 