Johann Baptist Cysat

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Johann Baptist Cysat (Latinized as Cysatus; in French, Jean-Baptiste Cysat) (c. 1587 – March 17, 1657) was a Swiss Jesuit mathematician and astronomer, after whom the lunar crater Cysatus is named. He was born in Lucerne, as the eighth of 14 children, to cartographer, historian and folklorist Renward Cysat (1545–1614).

In 1604, Cysat joined the Jesuits and became a theology student in March 1611 in Ingolstadt. There he met Christoph Scheiner, whom he assisted in the latter’s observation of sunspots, whose discovery would later become a matter of dispute between Galileo and Scheiner.

In 1618, Cysat was named professor of mathematics at the University of Ingolstadt, succeeding Scheiner in this position, thereby allowing him to concern himself further with astronomical problems. Cysat became one of the first to make use of the newly developed telescope.