Translation guide
The semi-major axis is a technical term from geometry and astronomy. In Japanese, it is expressed using the standard mathematical term 半長軸 (はんちょうじく). This guide covers the primary term and related expressions.
The half of the longest diameter of an ellipse, or the average orbital distance in astronomy.
The semi-major axis of a planet's orbit is related to its orbital period.
The orbital semi-major axis is an important parameter that indicates the size of the orbit.