Celestial Sphere

6.7 - Understand the meaning of the terms:
a) celestial sphere
b) celestial poles
c) celestial equator

5.6 - Understand the terms First Point of Aries and First Point of Libra

The Celestial Sphere is an imaginary sphere around Earth. We can imagine that all natural objects in the sky can be plotted on this so we can measure and understand their apparent positions.

Our poles are projected outwards to the sky and known as celestial poles. Likewise our equator is projected outwards and known as the celestial equator.

There are two coordinate systems we use in astronomy: