Definition:Nadir

Definition
Consider the celestial sphere $C$ with an observer $O$ at the center.

Let $Z$ be the zenith of $C$

Let the straight line $ZO$ be produced from $O$ to meet $C$ at $R$.

The point $R$ is known as the nadir of $C$.


 * Celestial-Sphere.png

In the above diagram, the nadir is indicated by $R$.

Also see

 * Definition:Zenith