zenith

The zenith is the point in the celestial sphere directly above you (or expressions like "the zenith at some place, at some time" indicate the above-defined zenith if you were at that place, at that time). In the horizontal coordinate system, any coordinate with altitude 90° indicates the zenith. Its equatorial coordinates constantly change, in a daily cycle of constantly changing right ascensions (diurnal motion), with additional very slow coordinate changes due to the precession of the equinoxes. The nadir (of the celestial sphere) is the direction opposite the zenith, i.e., straight down through the Earth.

The word zenith is also used for the highest point a celestial body reaches in the sky, e.g., on a particular day, such as the Sun reaching its zenith.