Z

zenith

in general, the point directly overhead on the celestial sphere.

zenith, astronomical

the extension to infinity of a plumb line from an observer’s location.

zenith, geocentric

The point projected onto the celestial sphere by a line that passes through the geocenter and an observer.

zenith, geodetic

the point projected onto the celestial sphere by the line normal to the Earth’s geodetic ellipsoid at an observer’s location.

zenith distance

angular distance on the celestial sphere measured along the great circle from the zenith to the celestial object. Zenith distance is 90° minus altitude.