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"51 unfolded engraved plates of celestial constellations by Alexander Mair. The very rare fourth edition of Bayer's Uranometria (first published in 1603), the first atlas to cover the entire celestial sphere, in fifty-one star charts, including one containing twelve new constellations unknown to Ptolemy. The illustrations are based on Jacob de Gheyn's designs for the Grotius edition of Aratus, published in Leiden in 1600. Johann Bayer (1572-1625) practised as a lawyer in Augsburg, but his principal interest was in the rapidly developing field of astronomy. His most important innovation was a new system of identifying all stars (prior to the invention of the telescope) by Greek and Roman letters, known today as the Bayer designation. The 1655 edition is much rarer than the 1661 edition" (Milestones of Science Books). "Bayer's was the first accurate star atlas. Earlier star catalogues followed Ptolemy's Almagest in using verbal descriptions to describe the location of stars within the 48 northern constellations of classical astronomy, an awkward system that occasioned constant errors and misapprehensions. Bayer, a lawyer and amateur astronomer, was the first to identify the location of stars within a constellation by the use of Greek letters (with the addition of the Latin alphabet for constellations with more than 24 stars). This simple innovation greatly facilitated the identification of stars with the naked eye, just five or six years before the invention of the telescope, and Bayer's stellar nomenclature is still in use today. Bayer used Brahe's recent observations for the northern sky, and included, in chart 49, twelve new southern constellations observed by the Dutch navigator Pieter Dirckzoon Keyzer and reported by Pedro de Medina. To simplify identification of the stars Bayer included in his typographic descriptions both the traditional star numerations within each constellation and the many names for the constellations employed since Ptolemy (Christies). The Uranometria was reprinted in 1639, 1648, 1655 (this copy) and 1661. Constellations largely identified by cataloger.

Deborah Warner, The sky explored: celestial cartography 1500-1800 pp. 18-19