Semi-Major Axis - Ellipse


In geometry, the major axis of an ellipse is the longest diameter: a line (line segment) that runs through the center and both foci, with ends at the widest points of the shape. The semi-major axis is one half of the major axis, and thus runs from the centre, through a focus, and to the edge of the ellipse; essentially, it is the radius of an orbit at the orbit’s two most distant points. For the special case of a circle, the semi-major axis is the radius. One can think of the semi-major axis as an ellipse’s long radius.

Related formulas


asemi-major axis (m)
lsemi-latus rectum (m)
ϵeccentricity (dimensionless)