Cysat, Johann Baptist

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Cysat, Johann Baptist

(b. Lucerne, Switzerland, ca. 1586; d. Lucerne, 3 March 1657)


Cysat’s father, Renward Cysat., was a man of letters and civic leader in Lucerne, and a vigorous sponsor of the Jesuit college there. Johann Baptist entered the Jesuit order in 1604; and in 1611 he was at the Jesuit college in Ingolstadt as a pupil of Christoph Scheiner, whom he assisted in the observation of sunspots. In 1618 Cysat become professor of mathematics at Ingolstadt. where he made the observations on the comet of 1618–1619 for which he is mainly known. He reports and analyzes these observations in an eighty–page booklet, Mathemata astronomica… (1619).

The observations cover the interval from 1 December 1618 to 22 January 1619, and form the most nearly continuous series of observations on this much argued–about comet. For each determination of position, Cysat measured the distance of the comet from two fixed stars, using a wooden sextant of six–foot radius. Calculating from Tycho’s star catalog, he found that the comet had moved from 9° 24´M,11° 37´ N. lat. on 1 December, to 21° 20´ , 56° 22´N. lat. on 22 January at a gradually decreasing rate. He also measured the dimensions of the head and tail and studied the appearance of the comet telescopically.

A major aim of Cysat’s analysis was to how to show that the comet was supralunary. He attempted to determine the true motion from observations on consecutive days when the comet had the same zenith distance; by comparison of the observed apparent motion in the course of a few hours with the calculated true motion he arrived at a figure for the difference in parallax. His procedure lacked mathematical rigor and was later sharply criticized in Riccioli’s Almagestum novum (I, 102–109). From the horizontal parallaxes Cysat derived earth–comet distances and then (assuming Tycho’s erroneous solar parallax) sun–comet distances. On the basis of these results he proposed two different theories for the comet: a Tychonic–style circular orbit about the sun, located between Venus and Mars, and a straight–line trajectory that fits the observations of 1, 20, and 29 December. The latter theory differs from the rectilinear trajectories espoused by Kepler because Cysat assumed that the earth was immobile.

His telescopic observation led Cysat to picture the nucleus of the comet as breaking into discrete stellulae from 8 December on—a phenomenon doubted by Robert Hooke and more recent astronomers. Cysat compared this appearance with that of nebulae in Cancer, Sigittarius, and the sword of Orion; he was once credited with the first reference to the Orin nebula, but this had already been observed in 1610 by Peiresc.

Cysat’s astronomical observations continued in later years but apparently did not appear in another published work. He described a lunar eclipse of 1620 in a letter to Kepler; Remus Quietanus and Kepler in 1628–1629 discussed his determinations of apparent planetary diameters; he observed the transit of Mercury of 1631; Riccioli referred critically to his excessive figures for apparent solar diameters, pointing out that they failed to take account of the diffraction of light discovered in the 1650’s by Grimaldi (Astronomia reformata, pp. 39–41). Meanwhile, Cysat served in many administrative capacities; he was rector of the Lucerne Jesuit college from 1623 to 1627; architect of the Jesuit college church built in Innsbruck in the 1630’s; rector of the Innsbruck Jesuit college from 1637 to 1641; and rector of the Eichstadt Jesuit college from 1646 to 1650.


Orginal Works. Cysat’s cometary work is Mathemata astronomica de loco, motu, magnitudine, et causis cometae qui sub finem anni 1618 et initium anni 1619 in coelo fulsit… (Ingolstadt, 1619). A Tabula cosmographica versatilis by Cysat is listed in Philippe Alegambe, Bibliotheca scriptorum societatis lesu(Antwerp, 1643), p.223. A “Clavis mathematica,” approved by the censors in 1634, apparently was never printed; and a work intended to show the providence of God in the arrangement of the world, mentioned by Cysat as being in preparation in 1636, also failed to appear in print. A letter of Cysat to Keplar and several letters referring to Cysat’s observations are published in Max Caspar, ed., Johannes Keplers gesammelte Werke,, XVII (Munich, 1955), nos. 838, 840; and XVIII(1959), nos. 910, 1095, and 1103. A collection of Cysat manuscripts at the Universitätsbibliothek in Munich is mentioned by Braunmuhl in Jahrbuch für Münchener Geschichte (Munich, 1894), pp. 53 ff.

II. Secondary Liturature. For details of Cysat’s life and work see Bernard Duhr, S. J., Geschichte der Jesuiten in den Ländern deutsche Zunge (Freiburg im Breisgau, 1907–1913), passim; Rudolf Wolf, Biographien zur kulturgeschichte der Schweiz, I (Zurich, 1858), 105–118; and Geschichte der Astronomie (Munich, 1877), pp. 319–320, 409,419; J. H. von Mädler, Geschichte der Himmelskunde, I (Brunswick, 1873), 295, 312; and M. W. Burke–Gaffney, S. J., Kepler and the Jesuits (Milwaukee, Wis., 1944), pp. 113–119. On the arguments over the 1618 comet, see Stillman Drake and C. D O’Malley, The Controversy on the Comets of 1618 (Philadelphia, 1960). On the problems of cometry astronomy before Newton, see James Alan Ruffner, The Background and Early Development of Newton’s Theory of Comets, Ph.D. dissertation (indian University, 1966).

Curtis Wilson