William is most notable for his
patronage of the arts and sciences. As a youth he had cultivated close connections with scholars and as a ruler he kept up this connection. His interest in astronomy may have been inspired by
Petrus Apianus's
Astronomicum Caesareum. William was a pioneer in
astronomical research, and perhaps owes his most lasting fame to his discoveries in this branch of study. Most of the mechanical contrivances which made instruments of
Tycho Brahe so superior to those of his contemporaries were adopted in
Kassel about 1584. From then on, the observations made in Hesse-Kassel seem to have been about as accurate as those of Tycho. However, the resulting longitudes were 6' too great in consequence of the adopted solar parallax of 3'.
Hessian star catalogue The principal product of the astronomical observations was the Hessian star catalogue, a catalogue of about a thousand stars. The locations were determined by the methods usually employed in the 16th century, connecting a fundamental star by means of
Venus with the sun, and thus finding its longitude and latitude, while other stars could at any time be referred to the fundamental star. It should be noticed that clocks, on which Tycho depended very little, were used at Kassel for finding the difference of
right ascension between Venus and the sun before sunset. Tycho preferred observing the angular distance between the sun and Venus when the latter was visible in the daytime. The Hessian star catalogue was published in
Historia coelestis (Augsburg, 1666) by
Albert Curtz, and a number of other observations are to be found in
Coeli et siderum in eo errantium observationes Hassiacae (Leiden, 1618), edited by
Willebrord Snell. R. Wolf, in his
Astronomische Mittheilungen, No. 45 (Vierteljahrsschrift der naturforschenden Gesellschaft in Zurich, 1878), has given a resume of the manuscripts still preserved at Kassel, which throw much light on the methods adopted in the observations and reductions. ==Botanical work==