AstrometricJ2000 is a utility function for computing astrometric coordinates.

Length1 returns Ramanujan's approximation for the length of an elliptical orbit.

Length2 returns an alternate approximation for the length of an elliptical orbit.

Length4 returns the length of an elliptical orbit.

Position returns observed equatorial coordinates of a planet at a given time.

Velocity returns the velocity of a body at aphelion.

Velocity returns instantaneous velocity of a body in elliptical orbit around the Sun.

Velocity returns the velocity of a body at perihelion.

Elements holds keplerian elements.