I don't think I've ever written a joint book review here, but since the two under discussion came out right around the same time and cover pretty much the same ground, I'm going to make an exception. Mark Anderson's The Day the World Discovered the Sun: An Extraordinary Story of Scientific Adventure and the Race to Track the Transit of Venus (Da Capo Press, 2012) and Andrea Wulf's Chasing Venus: The Race to Measure the Heavens (Knopf, 2012) both take as their subject what Wulf calls "the most ambitious scientific project that had ever been planned" (xxv): the international efforts to observe the 1761 and 1769 transits of Venus.
Both books are written with a popular audience in mind, and both succeed at explaining the importance of the transit observations and profiling some of the many observers who made the attempts. Both cover a great deal of ground in not a lot of space, so they tend to get a bit choppy in parts. That said, both also make for pleasurable reading, but in the end I found myself preferring Wulf's narrative to Anderson's.
Wulf's book is structured a bit more clearly, and she manages to profile a few more observers than Anderson, including those in what would become the United States and Canada (her anecdote about David Rittenhouse getting so excited just as the 1769 transit started that he fainted may be the best one of all of them). Anderson has a bit more on the French expedition to Baja California and Maxmilian Hell's trek to the far north of Norway, on the other hand. Both do quite well on Cook's journey to Tahiti, and in general on the organizational efforts that went into planning the various expeditions.
Wulf integrates illustrations into the text, which is a nice touch (though the reproduced maps are printed a bit too small and some of the illustrations are fairly tangential). She also provies good overview maps of the various observation points, comprehensive lists of the observers, and a very extensive bibliography/notes section. She recommends (and I've just spent way too much time enjoying) Rob van Gent's amazing bibliographic list of known original reports of the 1761 and 1769 transits (often with links out to the texts themselves).
I read Anderson's book last weekend, but knowing that I was going to spend yesterday afternoon (5 June 2012) on a train from New York to Charlottesville, during which the last transit of Venus would occur, I reserved Wulf's book to read then, and was really glad that I had. Sadly, the transit was obscured by clouds for me, so I've missed my chance now to see the spectacle (barring any fantastical medical advances which would keep me around until 2117, which seems an unpleasant idea). But as I watched the clouds, hoping they'd break briefly, I was reading of the French observer Le Gentil. In 1761 he never made it to a stable observation point and watched the transit from the deck of a ship in the Indian Ocean, unable to get reliable data. Spending the next eight years making preparations, in 1769 he was in Pondicherry, India ... where the transit was completely obscured by clouds.
I'd recommend either book without reservation to anyone interested in the topic. Wulf's came out a bit higher on my own reading scale, but your mileage may vary. Both tell a fascinating story well worth reading and exploring further.