Johann Baptist Cysat

Johann Baptist Cysat (about 1587 to 1657), also Cysatus, was a Swiss Jesuit mathematician and astronomer born in Lucerne, the eighth of fourteen children of the cartographer, historian and folklorist Renward Cysat. He joined the Jesuits in 1604 and became a theology student at Ingolstadt in 1611, where he met Christoph Scheiner and assisted his observations of sunspots, a discovery later disputed between Galileo and Scheiner. In 1618 he succeeded Scheiner as professor of mathematics at the University of Ingolstadt and became one of the first to use the newly developed telescope. His most important work was on comets: he observed the comet of 1618, published a monograph on it in 1619, held that comets circle the sun, showed that the orbit of the comet was parabolic rather than circular, and was the first to describe cometary nuclei. The lunar crater Cysatus is named after him.