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