These 3 broadsides, issued approximately 2 weeks apart, contain the first detailed illustrations of Mars. Although the patches do not correspond to actual features discernible today, Cassini used them to determine that Mars rotates on its own axis, inclined to the ecliptic, with a period of 24 hours, 40 minutes (only 3 minutes off the present value). At this time, Cassini was a professor of astronomy at the University of Bologna, using a 17-foot telescope crafted by Giuseppe Campani. In 1671, he became the founding director of the Paris observatory. In addition to discovering 4 additional moons of Saturn, he discerned the major break in Saturn’s ring now known as the Cassini gap.