In an ellipse
, the major axis
is the longest line running
through its center and two foci
passing through the widest part of the shape
The minor axis is the line through the center of the ellipse perpendicular to the major axis.
It follows then that the semimajor and semiminor axes are half the major and minor ones, each running from the center of the ellipse to their respective points on the edge.
OK, you may say. So what's it good for?
They are useful in calculating the area and the perimeter of an ellipse. See? Look.
Area = pi(semimajor axis * semiminor axis)
and where a equals the semimajor axis and b equals the semiminor axis a simple approximate value for the perimeter is
Perimeter = (2 * pi) (sqrt(a² + b² / 2))
Which, if you are a geometry geek
, is plenty.