Definition:Cardinal Directions
Definition
The $4$ cardinal directions:
are the basis of navigation and geographical coordinates.
Cardinal Directions (Terrestrial)
The $4$ cardinal directions are the directions on (or near) Earth's surface defined as follows:
East
East is the direction on (or near) Earth's surface along the small circle in the direction of Earth's rotation in space about its axis.
West
West is the direction on (or near) Earth's surface along the small circle in the opposite direction from Earth's rotation in space about its axis.
North
North is the direction on (or near) Earth's surface along the meridian directly towards the North Pole.
South
South is the direction on (or near) Earth's surface along the meridian directly towards the South Pole.
Cardinal Points (Celestial)
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 known as
The (terrestrial) cardinal directions are often referred to as the cardinal points, despite the fact that they are not actually points.
The (celestial) cardinal points are also seen referred to as the cardinal directions when the context refers to the direction towards those cardinal points.