semimajor axis

semimajor axis

Half the longest distance (major axis) across an ellipse.
The semimajor axis is one of the orbital
elements – a standard parameter used to describe an elliptical
orbit. The semimajor axis is also the average distance of an orbiting object
from its primary. The periapsis and apoapsis
distances, r_{p} and r_{a}, can be calculated
from the semimajor axis, a, and the eccentricity, e, by the
formula
r_{p} = a(1  e) and r_{a}
= a(1 + e)
Related category
• CELESTIAL
MECHANICS 