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.