Cardinal Points, Culmination, Meridian, Zenith and Circumpolarity

Cardinal Points

Cardinal Points are the four main points on the compass: North, South, East, and West.
These points are essential for navigation and understanding in what direction celestial bodies rise and set.

Culmination, in celestial terms, refers to when an object reaches its highest point in the sky.
It usually reaches this point due to the rotation of the Earth.
There is an Upper Culmination when the celestial body is visible and a Lower Culmination when it’s not visible.
Culmination occurs when the celestial bodies cross the observer’s meridian.

The Meridian is an imaginary line that is drawn from the North Point, through the zenith, to the South Point.
It divides the sky into the Eastern and Western halves.
Celestial bodies culminate when they cross this meridian, indicating their highest or lowest point in the sky.

The Zenith is the point in the sky directly above the observer.
It is the extreme opposite of the nadir, which is the direction pointing directly below the observer.
The horizon’s plane is perpendicular to the line from the nadir to zenith.

Circumpolarity refers to stars and constellations that, as observed from a given latitude on Earth, never set below the horizon due to their proximity to one of the celestial poles.
Whether a star is circumpolar or not depends on its declination and the observer’s latitude.
Stars that are closer to the North or South celestial pole are more likely to be circumpolar.
For example, from the UK, the northern polar star Polaris, and constellations like Ursa Major and Ursa Minor are circumpolar.