To be in an orbit, an object needs to satisfy the orbit equation.

1. To be in an orbit, an object needs to satisfy the orbit equation. In other words, our planet's rotation around the sun, our moon's rotation around earth, and all other countless orbital phenomenons in the galaxy where the bodies are not neither crashing into nor fading from their orbital partner, must perfectly satisfy this equation.




where:
u=reciprocal of the distance between the two objects.
e=the eccentricity of the orbit
a=the semi-major axis of the orbit (taken negative for a hyperbola)
theta=the true anomaly, which is an angular parameter that defines the position of a body moving along a Keplerian orbit