Energy determines whether an orbit is bound or not. Circles and ellipses are the only bound orbits; parabolae and hyperbolae are the only unbound ones. Note that orbits (rectilinear or straight-line orbits) may be elliptical, parabolic, or hyperbolic.
Bound Orbits () | Unbound Orbits () | |||
Circle | Ellipse | Parabola | Hyperbola | |
Semimajor Axis: | ||||
Eccentricity: | ||||
Distance: | ||||
Speed: | ||||
( in the limit , i.e., speed at ``infinity'')