AS a service to his fellow comet hunters, Charles Messier compiled a list of heavenly bodies that they might otherwise mistake for the fuzzy splodge of a comet. Messier discovered 15 comets (12 of them bear his name) and was so successful that Louis XV called him the 鈥渇erret of comets鈥�. But the ferret had his failures: he wasn鈥檛 the first to spot Halley鈥檚 Comet on its return in 1758.
Enter Stephen O鈥橫eara, one of today鈥檚 best visual observers. He succeeded where Messier failed: in 1985 he was the first to see Halley鈥檚 Comet since 1911. O鈥橫eara is uniquely qualified to pay tribute to his illustrious forebear.
The 110 Messier objects make up the meat of O鈥橫eara鈥檚 Deep Sky Companion (CUP, 拢19.95, ISBN 0521553326). All the essentials are here: how to find an object, how big it is, how far away and so on. Even Messier鈥檚 original entry is reproduced. His catalogue numbered 39 galaxies, 57 star clusters, 9 nebulae, a supernova remnant (the famous Crab Nebula, which is M1), a swathe of the Milky Way, a tiny grouping of stars, a double star and a duplication. This gives us a total of 109 (there鈥檚 that duplication, remember).
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What is fascinating is why Messier missed obvious objects yet included others so decidedly uncomet-like. A practical exercise ends the book: 鈥淓ach spring,鈥� says O鈥橫eara, 鈥渁mateur astronomers around the world run a marathon-not the gruelling 26-mile-long race, but a visual race through the night sky to glimpse all 109 Messier objects in a single night.鈥� No doubt these masochists know the Messier objects by heart. For anyone else, O鈥橫eara鈥檚 book will be an invaluable guide to some of the finest showpieces in the heavens.