# Definition:Cardinal Points (Celestial)

## Definition

The **cardinal points** of the celestial sphere are the **north point**, the **south point**, the **east point** and the **west point**:

### North Point of Horizon

The point on the celestial horizon through which the principal vertical circle passes is called the **north point of the horizon**.

### South Point of Horizon

The point on the celestial horizon exactly opposite the **north point of the horizon** is called the **south point of the horizon**.

### East Point of Horizon

Let an observer $O$ be facing the **north point of the horizon** $N$, facing directly away from the **south point of the horizon** $S$.

Let the celestial equator meet the celestial horizon at the points $E$ and $W$.

Let $E$ be the point on the right of $O$.

This is called the **east point of the horizon**.

### West Point of Horizon

Let an observer $O$ be facing the **north point of the horizon** $N$, facing directly away from the **south point of the horizon** $S$.

Let the celestial equator meet the celestial horizon at the points $E$ and $W$.

Let $W$ be the point on the left of $O$.

This is called the **west point of the horizon**.

## Also see

- Results about
**celestial cardinal points**can be found**here**.

## Sources

- 1976: W.M. Smart:
*Textbook on Spherical Astronomy*(6th ed.) ... (previous) ... (next): Chapter $\text {II}$. The Celestial Sphere: $18$.*Altitude and azimuth.*

- 1998: David Nelson:
*The Penguin Dictionary of Mathematics*(2nd ed.) ... (previous) ... (next):**cardinal points**:**2.** - 1998: David Nelson:
*The Penguin Dictionary of Mathematics*(2nd ed.) ... (previous) ... (next):**celestial sphere** - 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next):**cardinal points**:**2.** - 2008: David Nelson:
*The Penguin Dictionary of Mathematics*(4th ed.) ... (previous) ... (next):**celestial sphere**