ZENITH

(From the Arabic.) In Astronomy, the top of the heaven, or vertical point; the point directly over head. The zenith is that point of the celestial sphere which would be intersected by the plumb line, supposed to be indefinitely extended. It may also be defined as the pole of the horizon, from which it is 90° distant. All vertical circles or azimuths nece arily pa through the zenith. [s. 1362]