天てん底てい

noun

nadir

Astronomical term for the point directly opposite the zenith, i.e., the lowest point in the sky relative to the observer.

• 天てん底ていは観かん測そく者しゃの真ま下したにあたる天てん球きゅう上じょうの点てんです。

  The nadir is the point on the celestial sphere directly below the observer.