JUNE 8, 2004, VENUS IN TRANSIT

Mathematician Maor (e: The Story of a Number, 1994) turns his attention to astronomy in this enlightening account of the

transits of Venus that have taken place over the past five centuries. A transit of Venus occurs when the planet moves into alignment between Earth and the Sun and crosses the solar disc as an exquisite black circle. Only five transits of Venus have been recorded since the development of telescopes, but knowledge of planetary orbits, periods of revolution, and positions against the fixed stars enable accurate predictions of their occurrence: The last was in 1882, the next will be in 2004. Early on, Edmond Halley proposed using transits of Venus to calculate the distance from Earth to the Sun—the so-called "astronomical unit," which would enable scientists to measure the actual size of the solar system. Maor provides the details of past sightings, beginning in 1639 with an obscure English astronomer named Jeremiah Horrocks (who witnessed the first recorded transit), and continuing to the 19th century, by which time politics, prestige, and international competition led to numerous expeditions to the farthest reaches of the planet. Unfortunately, Halley's dream of calculating the astronomical unit would be daunted by the vagaries of weather, which all too often produced perverse cloud cover at the magic moments. Furthermore, Earth's own atmosphere (as well as that of Venus) would make precise measurements impossible. Nevertheless, some measurements did come reasonably close to the figure of 93 million miles for the astronomical unit—a number now obtained with great accuracy through laser and radar measurements. Maor's book has much of the flavor of Dava Sobel's Longitude (1995), a wonderful reading of human ingenuity in the face of a challenging problem. Instead of a single hero who triumphs, however, Maor’s cast includes amateurs and professionals, clergymen and sea captains, the wrongheaded and the brilliant—with every one of them lucky enough to witness a transit glorying

in their view.