Figure 4-17: Early Observations of Jupiter’s Moons In 1610 Galileo discovered four “stars” that move back and forth across Jupiter from one night to the next. He concluded that these are four moons that orbit Jupiter, much as our Moon orbits Earth. The circle represents Jupiter and the dots its moons. Compare the drawing numbered 7 with the photograph in Figure 4-16.
(Royal Astronomical Society/Science Source)