The Terrestrial Sphere & The Celestial Sphere

The shape of Earth is spheroid like an orange, a bit flat on the poles. The sphere of Earth is called The Terrestrial Sphere.

The celestial sphere is an imaginary sphere with the earth at its center. 

 

Terrestrial and Celestial Equators

Terrestrial Equator is an imaginary great circle on the surface of earth, which divides the earth into two equal halves (Hemispheres), and its poles are at the centre of both the flat portions.

The Celestial Equator is an imaginary line around the middle of the Celestial Sphere

The Celestial Equator is like earth's equator, but at a much greater radius.

Celestial Pole

    The celestial poles are imaginary lines that trace the Earth’s rotation axis in space. The Earth has two celestial poles – the Northern Celestial Pole and the Southern Celestial Pole. At the moment, these poles correspond to the geographical North and South Pole. Because of this, objects that lie on the celestial pole do not seem to move at all for observers on Earth, while all other objects, mostly stars, seem to move in a circle around the pole.

Celestial Sphere

    The celestial sphere is an imaginary sphere that extends infinitely into space with the Earth at its center.