Depth perception fails us for the distant objects we see in the sky.
This creates the appearance that all of the stars have the same distance.
Only a few centuries ago astronomers came to realize that the stars are actually very far away, scattered throughout the Milky Way Galaxy, rather than attached to the inside of a vast sphere. The concept of the celestial sphere provides a simple way of thinking about the appearance of the stars from Earth without the complication of a more realistic model of the universe.
Working with the celestial sphere offers a convenient way of describing what we see from Earth.
When we refer to the celestial sphere, we are imagining that everything we see on the sky is set on the inside of a huge spherical shell that surrounds the Earth.
A woman walking home late at night is attacked by an unknown assailant who knocks her out with chloroform.
When she regains consciousness, she finds herself tied to a bed in a blood- ... our origin..." and proceeds to depict the first violent formation of matter from nothingness.