鉛えん直ちょく圏けん

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.

• 天てん文もん学がくでは、鉛えん直ちょく圏けんは天てん体たいの高こう度どを測はかる基き準じゅんとして使つかわれる。

  In astronomy, the vertical circle is used as a reference for measuring the altitude of celestial bodies.