Striking star chart showing the Constellation Hercules, from Bayer's Uranometria, one of the most important of all Celestial Atlases.
Bayer's Uranometria was one of the most important early Celestial works. The Atlas contained 51 star charts, of which 48 were Ptolemaic constellations. Each plate has a carefully engraved grid, so that star positions can be read off to fractions of a degree. These positions were taken from the catalog of Tycho Brahe, which had circulated in manuscript in the 1590s, but which was only printed in 1602.
Another important feature of the atlas was the introduction of a new system of stellar nomenclature. Bayer assigned Greek letters to the brighter stars, generally in the order of magnitude, so that the bright star in the Bull's eye became alpha Tauri, the brightest star in the Centaur became our familiar alpha Centauri, etc. These letters were placed on the charts themselves, and also in a table that accompanied each chart.