Uranometria

Uranometria is the short title of a star atlas produced by Johann Bayer. It was published in Augsburg, Germany, in 1603 by Christophorus Mangus under the full title Uranometria : omnium asterismorum continens schemata, nova methodo delineata, aereis laminis expressa. This translates to "Uranometria, containing charts of all the constellations, drawn by a new method and engraved on copper plates". The word "Uranometria" derives from Urania, Muse of the heavens and "uranos" (oυρανός) the Greek word for sky / heavens. A literal translation of "Uranometria" is "Measuring the Sky" (to be compared with "Geometry"-"Geometria" in Greek, literally translated to "Measuring the Earth").

It was the first atlas to cover the entire celestial sphere.

The pages of Uranometria were originally engraved on copper plates by Alexander Mair (ca 1562-1617). It contained 51 star charts. The first 48 pages represent the 48 Ptolemaic constellations. The 49th page introduces 12 new constellations in the deep southern sky which were unknown to Ptolemy. The final two charts are planispheres labeled "Synopsis coeli superioris borea" and "Synopsis coeli inferioris austrina," or (roughly), "Overview of the northern hemisphere" and "Overview of the southern hemisphere."

Each plate includes a grid for accurately determining the position of each star to fractions of a degree. The positions used by Bayer to create the Uranometria were taken from the expanded 1,005 star catalog of Tycho Brahe. Brahe's expanded list had circulated in manuscript since 1598 and was available in graphic form on the celestial globes of Petrus Plancius, Hondius, and Willem Blaeu. It was first published in tabular form in Johannes Kepler's Tabulae Rudolphinae of 1627.

The use of Brahe's catalog allowed for considerably better accuracy than Ptolemy's somewhat limited star listing. The stars listed in Uranometria total over 1,200, indicating that Brahe's catalog was not the only source of information used. Bayer took the southern star positions and constellation names for the 49th plate from the catalog of Dutch navigator Pieter Dirkszoon Keyser, who corrected the older observations of Amerigo Vespucci and Andrea Corsali, as well as the report of Pedro de Medina. Uranometria contains many more stars than did any previous star atlas, though the exact number is disputed as not all stars on the charts are labeled.

Each of the constellations' stars are overlayed on an engraved image of the subject of the constellation. For reasons unknown, many of the human constellations are engraved as figures seen from behind whereas they had traditionally been rendered as facing the Earth. This oddity led to some confusion in the literal meanings of certain star names (e.g. the origins of several named stars refer specifically to "right shoulder" and the like, which would be incorrect given Uranometria's illustrations).

Uranometria introduced the Bayer star designations, which are still used today. It also introduced several of the modern constellations.