The entire sky is now divided into 88 Constellations defined by the IAU in 1922. But their history goes way back to prehistory. The Ancient Greeks combined the legends of Chaldea, Babylon and Egypt with their own and began to formalise a complete iconography of the sky as viewed from the Mediterranean. The stars were associated with mythological characters in a series of popular stories generally related to sex and/or violence. Perhaps the idea was to create a mental map of the sky, or in an age of primarily oral tradition, perhaps to use the stars as an aid in remembering the stories.
One of the first Greek astronomers to compile a catalogue of the visible stars was Eudoxus of Cnidus. Unfortunately his original work has not been preserved, but Aratus (apparently born in Solis in modern Turkey ca. 315 BC/310 BC – 240 BC) used this list to write a didactic poem, the Phaenomena, telling the stories. There's an on-line English translation at:
http://www.theoi.com/Text/AratusPhaenomena.html
By all accounts the poem was tremendously popular. A century later, Hipparchus (whose own star catalogue was used by Ptolomy) criticised its accuracy, but praised it as a literary work. It was translated into Latin by several distinguished Roman authors, including Cicero, and survived as one of the few astronomical texts in Western Europe during the Dark Ages. Early on, the poem was illustrated – and, although the original Greek and Roman examples have been lost, there are apparently more or less faithful later copies dating from the early 9th Century AD which are associated with the church and court of Charlemagne and his son, Louis the Pious.
Three of the best these manuscripts survive respectively at the University Library in Leiden, the British Library in London and the National Library in Madrid.
Hercules from the Leiden Aratus
The Madrid Aratus showing Eridanus, Pisces and Ara
Centaurus from the London Aratus
Although all are based on Aratus, the three are in fact very different, presumably copied from three distinct Late Roman sources. The Leiden Aratus is essentially a picture book in a small format, probably commissioned by a wealthy and important patron for personal enjoyment. The Madrid manuscript on the other hand is a collection of different works intended to aid “computus” or the astronomical calculation of the calendar and was probably produced as a result of a conference of clerics on the theme in Aachen in 809. The London manuscript ingeniously incorporates the pictures of the Constellations into calligrams, images made from words.
The Leiden Aratus was exhibited at the Getty Museum in Malibu. The catalogue with photos of most of the Constellations is available at:
http://www.getty.edu/publications/virtuallibrary/0892361425.html
The London Aratus is available as very detailed zoom-able scans at:
http://www.bl.uk/manuscripts/FullDisplay.aspx?ref=Harley_MS_647
Black and white photos of the Madrid Aratus are available at the Warburg Institute Iconagraphic Database:
http://warburg.sas.ac.uk/vpc/VPC_search/subcats.php?cat_1=9&cat_2=71&cat_3=32&cat_4=39&cat_5=975&cat_6=453&cat_7=245
The complete manuscript is digitally scanned at:
http://bdh-rd.bne.es/viewer.vm?id=0000122617&page=1