Puolipääakson

Puolipääakson, often translated as the "half-axis" or "semi-axis," is a term used in mathematics and physics, particularly in the context of ellipses and ellipsoids. It refers to half of the length of the major or minor axis of such a geometric shape. The major axis is the longest diameter of an ellipse, and the minor axis is the shortest diameter. The puolipääakson related to the major axis is called the semi-major axis, and the one related to the minor axis is called the semi-minor axis.

In the equation of an ellipse centered at the origin, the standard form is often written as (x^2/a^2) + (y^2/b^2) = 1. Here, 'a' represents the length of the semi-major axis if a > b, and 'b' represents the length of the semi-minor axis. Conversely, if b > a, then 'b' is the semi-major axis and 'a' is the semi-minor axis. The semi-major axis is crucial in defining the size and shape of an ellipse and is fundamental in orbital mechanics, where it determines the size of an orbit. For example, in Kepler's laws of planetary motion, the semi-major axis is a key parameter. The term is also applied in three dimensions to ellipsoids, where there are three semi-axes of different lengths.