Final answer:
The zenith is the point in the sky directly above an observer's head. It is part of the celestial sphere concept, where it represents the top of the dome of the sky.
Step-by-step explanation:
The point in the sky directly above your head at any given time is known as the zenith. This concept is a part of the celestial sphere model, where the sky is perceived as a dome enclosing the Earth. The zenith is at the top of this dome, while the horizon represents where the dome meets the ground. On this celestial sphere, the celestial poles are located 90° from the celestial equator, and are at the north and south points on the horizon if you are at the Earth's equator. As Earth rotates, all stars appear to move in paths across the sky, half of the time above and half below the horizon, except for those near the celestial poles which circle around the pole and do not rise or set.