Intricate tour of heaven

Maps have always been a vital part of the documentation of civilisation. Travellers, explorers, traders, hunters, warriors and holidaymakers all recorded their journeys using maps. These helped them pass on knowledge, and hopefully enabled other people to replicate those journeys without getting lost.

Celestial journeying is similar. Without sky maps our ancestors would have found it very difficult to teach others about the sky. Charting the risings, settings and circling that enabled the time to be told at night would have been difficult without a map. The speedy establishment of north, south, east and west and the calculation of the progressions of the seasons are also greatly helped by the availability of sky maps.

The shape of the sky above our horizon is similar to the shape of the Earth beneath our feet. Both are spherical and large and replete with diverse things. Earth is enlivened with villages, towns and cities, rivers, mountains and seas. Other aids to navigation are the boundaries between countries. The sky is full of stars, and astronomers have dragooned these into easily recognisable country-like constellations. Stars also have a range of brightnesses and are fortunately few in number; within the limitations of our naked eyes and environment we can usually see only a few hundred at any one time.

Luckily, the brighter stars appear to form strange, fixed and easily memorable patterns. Those stars reminded our ancestors of familiar things and they soon populated the celestial sphere with a menagerie of animals and a Valhalla of assorted gods and goddesses. Their imaginations even blossomed to include rivers, dragons, boats, crowns and astronomical instruments.

This is where the art came in. If a certain constellation was deemed to look like a great bear, then that bear needed to be drawn on the star map. As time passed, astronomical maps progressed from the mere functional and became objects of considerable beauty.

Nick Kanas is a collector of star maps and a cartographic connoisseur. His enthusiasm leaps from every page of this detailed investigation of the development of celestial prints and star atlases.

Star Maps starts with the earliest hand-drawn images, and then progresses through the ages of wood blocks, intaglios, engravings, lithography and modern printing. Potted biographies are provided for each map maker, and the relationship between the mapping techniques and the general advances of astronomical understanding is stressed.

Star Maps is an engaging and informative romp through the development of celestial cartography. But two things slightly worried me. The first is the format. The monotone and coloured images are much smaller than the maps as produced, and thus gave little indication of the breathtaking beauty and intricacy of the originals. Other recent books, such as Celestial Charts by Carole Stott (1991) and Maps of the Heavens by George Sergeant Snyder (1984), are much better in this respect.

The second is that Kanas conveys little of the purpose behind the original cartography. I did not pick up the urgency behind, say, John Flamsteed's Atlas Coelestis (1729) in the quest for a mechanism to find longitude at sea, or the excitement of Giuseppe Piazzi in realising that a "star" he had mapped in 1801 was actually racing across the sky, and so not a star at all but a dwarf planet orbiting between Mars and Jupiter, or Cambridge University's disappointment in overlooking the new planet Neptune in the 1840s, simply because its star maps were much inferior to the new German ones at the time.

Kanas clearly loves star maps, but I was not convinced that he had been forced to actually use them.

David W. Hughes is professor of astronomy, Sheffield University.