Celestial Navigation · Celestial Sphere — Definitions
The point on the celestial sphere directly overhead the observer is the:
- AZenith✓ Correct
- BNadir
- CCelestial pole
- DVernal equinox
Explanation
The zenith is the point directly above the observer; the nadir is directly below. The celestial poles are the projections of the Earth's poles, and the vernal equinox (First Point of Aries) is the reference for sidereal hour angle.
Authority: Bowditch (Pub. No. 9), The Celestial Sphere
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