[astronomy] In astronomy, the point on the celestial sphere directly above an observer. Both the zenith and nadir lie on the observer’s meridian; the zenith lies 180 degrees from the nadir, and is observable.
[astronomy] In astronomy, the point on the celestial sphere directly above an observer. Both the zenith and nadir lie on the observer’s meridian; the zenith lies 180 degrees from the nadir, and is observable.