noun
argument of periapsis
Technical term in astronomy and orbital mechanics; refers to the angle from the ascending node to the periapsis (closest point) of an orbit.
人工衛星の軌道要素の一つとして、近点引数が計算される。
The argument of periapsis is calculated as one of the orbital elements of the satellite.
Compound of 近点 (periapsis) + 引数 (argument, in the mathematical sense). The exact historical derivation is uncertain; the term is a modern technical coinage.