Figure 9-14 RIVUXG Tracking the Sun’s Rotation with Sunspots This series of photographs taken in 2001 by SOHO shows the rotation of the Sun. For comparison, a dot the size of Earth is added, showing how large sunspots can be—this sunspot group is more than 13 times larger than Earth. By observing the same group of sunspots from one day to the next, Galileo found 400 years ago that the Sun rotates once in about four weeks. (The equatorial regions of the Sun actually rotate somewhat faster than the polar regions.) Notice how the sunspot group shown here changed its shape.
(SOHO/ESA/NASA)