On June 6, 1761, the world paused to observe a momentous occasion: the first transit of Venus between the Earth and the Sun in more than a century. Through that observation, astronomers could calculate the size of the solar system—but only if they could compile data from many different points of the globe, all recorded during the short period of the transit. Overcoming incredible odds and political strife, astronomers from Britain, France, Russia, Germany, Sweden, and the American colonies set up observatories in the remotest corners of the world, only to be thwarted by unpredictable weather and warring armies. Fortunately, transits of Venus occur in pairs; eight years later, they would have another opportunity to succeed. Thanks to these scientists, neither our conception of the universe nor the nature of scientific research would ever be the same.