Review of Chasing Venus by Andrea Wulf (2012, William Heinemann)

When observing the transit of Mercury across the sun in the early 16th century, Edward Halley deduced that one could measure the size of the solar system by watching Venus’ transit.  Knowing this would increase the accuracy of the measurement of the heavens and also aid navigation and mapping the Earth.  The problem was that Venus only transits the sun periodically, in a pair of transits separated by eight years once every 105 years, and the full transit could only be observed from a few locations across the planet.  The next transits were due in 1761 and 1769, several years after Halley’s death.  The importance of accurately measuring the time of transit was acknowledged by astronomers and scientific societies.  It would require international cooperation to share the measurements and calculations.  And it would be costly, involving expensive clocks, surveying instruments, and telescopes, as well as transport and labour, and would need political and royal patronage.  An added difficulty was much of Europe was engaged in the seven years’ war preceding and during the first transit.  Despite this scientists agreed to collaborate despite the hostilities.

Chasing Venus tells the tale of the various attempts to measure Venus’ transits in 1761 and 1769, tracking the wider international collaboration, the perilous journeys undertaken to various parts of the globe by astronomers, and the scientific calculations undertaken.  Wulf does a good job at marshalling a lot of interrelated storylines and structuring it into an easy to follow narrative, giving a clear sense of the importance of the scientific task, the science involved, the lives of the main participants, and the wider political landscape.  Several astronomers risked their lives travelling to different sites and in the case of the 1769 expeditions five lost their lives, and all put up with various hardships without any guarantee of being able to observe the transit (and a number didn’t because of clouds).  In addition, the expeditions provided new knowledge about the South Seas and remote parts of Russia (Captain Cook’s first Endeavour voyage was to observe the transit in Tahiti).  While the book is well researched and written, the ending is a little abrupt and it would have been useful and interesting to find about a bit more about the significance of the science and expeditions, and the subsequent lives of the astronomers, even as just short potted biographies.  Overall, an interesting read.