In
astrodynamics or
celestial mechanics an
elliptic orbit is a
Kepler orbit with the
eccentricity less than 1; this includes the special case of a
circular orbit, with eccentricity equal to zero. In a stricter sense, it is a Kepler orbit with the eccentricity greater than 0 and less than 1 (thus excluding the circular orbit). In a wider sense it is a Kepler orbit with negative
energy. This includes the radial elliptic orbit, with eccentricity equal to 1.