Title: Coelum stellatum in quo asterismi I. Boreales, II. Zodiacales, III. Australes ... exhibentur / Opera M. Christophori Semleri...
Author: Semler, Christoph, 1669-1740.
Imprint: Halae Magdeburgicae ; [s.n.] , 1731.
Description: [2] p., [35] leaves of plates : ill. ; 21 cm.
Book location: QB65 .S45 1731 Rare Book Room

Celestial cartographer Christoph Semler is unknown except through his atlas. The Semler atlas is immediately distinguishable from all its predecessors by the black background on the plates. Each plate was printed from a woodblock, on which the outline of the constellation was cut, as well as a symbol for each star.  The rest of the block was uncut, which means it retained ink and printed black.  Each of the 35 woodcuts has a different oriention, which can sometimes be disconcerting, although celestial north is indicated by an arrow on each plate. Some of the illustrations are quite attractive, such as the one that depicts Centaurus, standing over the Southern Cross, engaging Lupus the Wolf.  Semler derived all of his constellations and star positions from the atlas of Hevelius, even including all nine of the new constellation figures that Hevelius introduced.  Hevelius, however, had depicted each  constellation as it would appear if viewed from outside, as on a globe.  Semler showed the constellations as they appear in the sky, from an observer on earth.  So all of Semler’s constellation figures are reversed from those of Hevelius.

• Adapted by William B. Ashworth from Out of This World: The Golden Age of the Celestial Atlas.