noun
vertical circle
Technical term in astronomy and surveying; a great circle on the celestial sphere passing through the zenith and nadir, perpendicular to the horizon.
天文学では、鉛直圏は天体の高度を測る基準として使われる。
In astronomy, the vertical circle is used as a reference for measuring the altitude of celestial bodies.
Compound of 鉛直 (vertical) + 圏 (circle, sphere). The exact historical derivation is uncertain; the term is a technical calque from Western astronomy.