# Definition:Celestial Pole

## Definition

Consider the celestial sphere $C$.

The celestial poles of $C$ are the north celestial pole and the south celestial pole:

### North Celestial Pole

Let $O$ be a celestial observer situated at the surface of Earth in the Northern hemisphere.

Let $OP$ be a straight line parallel to Earth's axis.

Let $P$ be the point in the visible hemisphere at which $OP$ meets the celestial sphere.

Then $P$ is the north celestial pole.

That is, the north celestial pole is the pole of the celestial equator which is the zenith of the North Pole.

### South Celestial Pole

Let $O$ be a celestial observer situated at the surface of Earth in the Southern hemisphere.

Let $OQ$ be a straight line parallel to Earth's axis.

Let $Q$ be the point in the visible hemisphere at which $OQ$ meets the celestial sphere.

Then $Q$ is the south celestial pole.

That is, the south celestial pole is the pole of the celestial equator which is the zenith of the South Pole.

In the above diagram, the celestial poles are the points $P$ and $Q$.