Figure 4-1:

A Merry-Go-Round Analogy (a) Two children walk at different speeds around a rotating merry-go-round with its wooden horses. (b) In an analogous way, the ancient Greeks imagined that the Sun and Moon move around the rotating celestial sphere with its fixed stars. Thus, the Sun and Moon move from east to west across the sky every day and also move slowly eastward from one night to the next relative to the background of stars.