Zenith

The zenith is the point on the celestial sphere directly overhead the observer, where the upward vertical from the observer’s position pierces the sphere, 90 degrees from every point on the celestial horizon. Its opposite below is the nadir. The zenith is one of the three vertices of the astronomical triangle, joined to the body by the zenith distance (the co-altitude) and to the pole by the co-latitude. A body at the zenith has an altitude of 90 degrees and a zenith distance of 0; the geographical position of any body is the point on Earth where that body is in the zenith.