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Fine example of the map of the Constellation Libra, from Bayer's Uranometria.
Perhaps the most illustrious of all celestial atlases is Bayer's Uranometria, the forerunner of all star atlases which contained 51 star charts, of which 48 were Ptolomeic 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 (and the brightest star in the Centaur became our familiar alpha Centauri.) These letters were placed on the charts themselves, and also in a table that accompanied each chart.
Libra has a rich and evolving history. While in modern times, it is illustrated as a balanced set of scales, Libra has been symbolized in varied ways over the past several thousand years. The ancient Greeks did not recognize Libra. Instead they saw it as part of Scorpius. Libra made up the two claws of the scorpion.
The Romans invented Libra and gave it importance as a constellation of the Zodiac. Libra was "the Scales of Justice" held by Julius Caesar. Later the scales became associated with Virgo, the Goddess of Justice. The Romans choose a scale because when the zodiac was still in its infancy, some four thousand years ago, the sun passed through this constellation at the autumnal equinox (September 21). As a symbol for equality, the constellation came to represent Justice in several middle Eastern cultures. The Egyptians also saw Libra as a set of scales, one in which the human heart was to be weighted after death, "the Scales of Justice."
