Semi-Major Axis

The Semi-Major Axis of an object's elliptical orbit is the distance from the center of the ellipse to the most distant point in the orbit. In other words, the Semi-Major Axis is half the distance between the pericenter and apocenter of the orbit. Semi-Major Axis is a way to represent the size of an orbit; objects with a smaller Semi-Major Axis will orbit closer to their Orbital Parent than objects with a larger Semi-Major Axis.

The Semi-Major Axis of an object with a hyperbolic trajectory is negative.

Semi-Major Axis is one of the six orbital elements that described an object's orbit.

Location
The Semi-Major Axis property is located in the Orbital Elements section of the Motion tab of an object's properties panel, if that object has an Orbital Parent.

Units
Semi-Major Axis can be viewed and edited using the following units:


 * Milky Way Galaxy radius (milky way) = 5.5×104 light year
 * Parsec (parsec) = 3.08568025×1016 m
 * Light-year (light year) = 9.46073047×1015 m
 * Astronomical Unit (AU) = 1.495978707×1011 m
 * Solar radius (sun) = 6.955×108 m
 * Lunar distance (lunar dist) = 3.844×108 m
 * Light-second (light sec) = 2.99792458×108 m
 * Jupiter radius (jupiter) = 6.9911×107 m
 * Earth radius (earth) = 6.37101×106 m
 * Moon radius (moon) = 1.7371×106 m
 * Kilometer (km) = 1000 m
 * Meter (m) is the SI base unit for length
 * Centimeter (cm) = 0.01 m
 * Millimeter (mm) = 0.001 m