Definition:Zenith

Definition
Let an observer $O$ on the surface of Earth be assumed to be the center of the celestial sphere $C$.

The zenith $Z$ is the point on $C$ which is vertically overhead. This can be determined by use of a plumb line.


 * Celestial-Sphere.png

In the above diagram, the zenith is indicated by $Z$.

Also see

 * Definition:Nadir