Basic Therminology of Astrology

Astrology is one of the part of primbon. Astrology deals with projective geometry, meaning distances to celestial bodies are inconsequential. Only their relative positions on the celestial sphere are important. In other words, only the angular differences from the Earth matter. We need to define certain key terms to obtain a graphical idea of the celestial sphere.

1. Celestial Sphere
The celestial sphere is an imaginary dome around an observer on Earth. The observer is at the centre of the dome, with all the visible celestial bodies on its surface. It is a model of how the sky appears to us. In reality, the various celestial bodies are not the same distance from the Earth.
2. Celestial Poles
The celestial poles are the centres of rotation of the celestial sphere. They are called the north and south celestial poles (NCP and SCP).

3. Zenith
The zenith is the point on the celestial sphere straight overhead of an observer on the Earth.

4. Nadir
The nadir is the point on the celestial sphere that is directly opposite the zenith.