Figure 2-9:

The Celestial Sphere The celestial sphere is the apparent sphere of the sky. The view in this figure is from the outside of this (wholly imaginary) sphere. Earth is at the center of the celestial sphere, so our view is always of the inside of the sphere. The celestial equator and poles are the projections of Earth’s equator and axis of rotation out into space. The celestial poles are therefore located directly over Earth’s poles.