Johann Baptist Cysat

Johann Baptist Cysat, Latinised as Cysatus, born at Lucerne around 1587 and dead on 17 March 1657, was a Swiss Jesuit mathematician and astronomer after whom the lunar crater Cysatus is named. 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 March 1611, where he met Christoph Scheiner and assisted him in his observation of sunspots. 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 and showed that the orbit of the comet was parabolic, not circular.