The celestial sphere is
a. a spherical galaxy, centered on the Sun.
b. the star-sphere discovered by the Greeks and other ancient civilizations which shows the physical location in space of the nearby stars.
b. the orb of the Sun; a normal star.
d. the central spherical region of the Milky Way Galaxy, dense with stars.
e. a useful illusion used to map the stars and other objects in the sky.