Because as the Earth rotates on its axis, it is the sky which APPEARS to revolve around the Earth each day.
(the Earth; rotates; L:on its axis) (it; is; the sky which APPEARS to revolve around the Earth each day) (the sky; APPEARS; to revolve around the Earth each day) (the sky; to revolve; around the Earth; T:each day)
the Earth it the sky the sky
rotates is APPEARS to revolve
L:on its axis
the sky which APPEARS to revolve around the Earth each day
to revolve around the Earth each day
around the Earth T:each day