Hey, so I have a question about motions of planets and their energy basically. When we have a circular orbit, why is it that the kinetic energy is just the opposite of potential energy? (Assuming it's a closed orbit) Like if we have U = something, than the kinetic energy T = -1/2U? This would be saying the kinetic energy doesn't change for a circular orbit but the potential energy does, and than I would think this would be a parabolic orbit as energy would then equal to 0 and epsilon (eccentricity) is equal to 1. I hope that made sense, I'm having trouble understanding such motion.