Posted on Wednesday 5 October 2005

Mapping the stars has always been an essentially part of astronomy but the 17th and 18th centuries was a golden age of the star atlas in which utility was intertwined with incandescent artistry. Based on ancient constellations as systematised by Ptolemy, the star atlas borrowed many elements from contemporary cartography and merged them observational data of unprecedented accuracy.

The format of the star atlas was essentially established by Johann Bayer in 1603 in his Uranometria which was based on the star catalogue of Tycho Brahe. Bayer established the nomenclature of naming stars with Greek letters according to the order of their brightness (for example, the brightest star in the Centaur constellation is known as Alpha Centauri). Bayer was also the first to include the stars and new constellations of the Southern Hemisphere. Incidentally, the Southern Cross, which is today a popular and defining symbol of the Antipodes (see here and here), was in ancient times been quite visible from the Northern hemisphere and comprised part of the back legs of the Centaur constellation. However, as a function of the Earth's precession it had slipped below the horizon only to be rediscovered by the new breed Christian voyagers. The Italian navigator Andreas Corsalis is said to have described the constellation as being "so fair and beautiful that no other heavenly sign may be compared to it". Bayer depicted the Cross over the legs of the Centaur.

Continuing this trend to reclaim the pagan heavens for the Christian Faith is the divinely inspired silliness of Julius Schiller who in 1627 produced an atlas which replaced the twelve signs of the zodiac with the twelve apostles, Jason's Argo Navis with Noah's Ark and so on. Bayer himself was quite enthusiastic about the project but, though beautifully executed, these new constellations never caught on.

The most influential star atlas after Bayer's was that of Johannes Hevelius in 1690. A great astronomer in his own right, he updated Bayer's star positions from his own observational data. He also completely revolutionised the treatment of the Southern Hemisphere but using the data collected by Edmond Halley in 1676 at St Helena. Hevelius' illustrations are also simply exquisite.

The last of the golden age atlases was by Johannes Bode who nearly exactly two hundred years after Bayer produced a beautiful atlas with over 17,000 stars. At this point it becomes evident that the illustrations are starting to detract from the usefulness of these charts as more and more data is packed into them. Later charts start to use simplified and more stylised representations of the constellations in order to provide more value to working astronomers - despite their considerable reduction in aesthetics.

A really good introduction to star atlases can be found at this online exhibit at the Linda Hall Library which is based on items from their collection. They also have five complete star atlases online, including one by Bayer.