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For millennia people have looked up at the stars in the night sky and seen patterns. Throughout the ages they have attributed various stories or myths to these groups of stars or asterisms. Over time many of the groupings gained names common to large groups of people and these were the first constellations.


Ancient Constellations

Originally pretty much any asterism would be a constellation. Any group of stars that could be easily recognizable would be named. Eventually over time, tradition and mythology began to fix the names of these constellations to particular asterisms. These names were passed on orally for generations until Ptolemy wrote them down around 150 CE. In his book the Almagest, Ptolemy described 48 constellations covering the night sky visible from Ancient Greece. Ptolemy's constellations dominated astronomical thought for the next 1500 years. Even the Arabian astronomer Al-Sufi used Ptolemy's constellations in his Ktab suwar al-kawakib (Book of the Fixed Stars).

In the 16th century, explorers were starting to bring back tales of the southern sky so new constellations needed to be created. Many different stellar cartographers came up with various new constellations and over the next 400 years various constellations came into existence when one noted cartographer placed in in his book, only to be changed when a later cartographer wrote yet another book. By the early 20th century there were generally agreed upon names for the constellations, but no definitive boundaries between what were still essentially asterisms[1] .

IAU Constellations

With no defined boundaries between constellations and with the telescope generating more and more astrometric data, there came a need to fix the boundaries between constellations. To this end the International Astronomical Union (IAU) commissioned Eugene Delporte to create these boundaries. Delporte did this and published the result in his book Delimination sientifique des constellations in 1930 [2].

What Delporte did was fix the sky into 88 constellations each with boundary lines that ran north-south and east-west. These boundaries generally encompassed the traditional asterisms of the constellations, but turned the constellation into a region of sky as opposed to merely a named asterism. This has allowed for more precise naming of stars and other objects as the constellation name is associated with a region and not just a grouping of stars.

See Also

List of Constellations


  1. Ridpath, Ian, Star Tales Web version at Accessed 11 June 2009
  2. IAU website, Constellations, Accessed 11 Jun 2009)
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