Saturn – William Sheehan ****

This book marks something of a milestone in my reviewing career: it’s the first time I’ve seen an excerpt from one of my reviews printed on the back cover. It comes from my review of Sheehan’s previous book, on Mercury, which I said ‘easily convinced me the Solar System’s 'least interesting' planet is still a pretty fascinating place.’ That wasn’t an easy task for the author, given Mercury’s unspectacular appearance and reputation – but Saturn is a different matter. With its iconic rings, easily visible through a small telescope, it’s the favourite planet of many amateur astronomers. For space scientists, too, it’s a prime target – given that two of its moons, Titan and Enceladus, look like the kind of places we might find alien life. So Sheehan’s challenge this time wasn’t to find enough material to fill 200 pages, but to distil a potentially huge subject down to that size.

He meets this challenge just as successfully as the previous one – but not quite in the way I was expecting. Instead of diving straight into the latest discoveries, the first third of the book – chapters 1 and 2 – consists of a leisurely stroll through the pre-space-age history of the subject, from ancient times to the middle of the 20th century. I enjoyed this more than I expected to, because it brought out just how slowly and painstakingly our understanding has been built up. One surprising revelation comes right at the start. For thousands of years, throughout the pre-telescopic era, it was Saturn – not Mercury – that had the reputation of ‘least interesting planet’. It’s the faintest of the ones that have been known since ancient times, and the one that changes position most sluggishly relative to the background stars. In fact Saturn’s reputation as the Solar System’s most spectacular planet is a hard-earned one. Even after its rings and moons were revealed by early telescopes, it was a long and laborious process to uncover their true nature, as astronomers’ instruments – and their understanding of physical laws – slowly improved over the course of centuries.

What I was really expecting to find in a book like this comes in the next two chapters – the middle third – with an in-depth look at the current scientific understanding of the planet and its rings. This perspective continues in the final third, with three shorter chapters on the Cassini mission, Saturn’s moons and the Saturn system as seen by amateur astronomers. The whole book is profusely illustrated – there must be at least a hundred images altogether, many in colour – and some of them are truly breathtaking.

All in all, I can recommend this book just as heartily as the Mercury one. This time, I didn’t need convincing that the subject was an interesting one – but I was still impressed by the way Sheehan manages to lay out all the important facts in such a methodical and unrushed way.

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Review by Andrew May