Space and time on earth are regulated by the prime meridian, 0°, which is, by convention, based at the Royal Observatory, Greenwich. But the meridian’s location in southeast London is not a simple legacy of Britain’s imperial past. Before the nineteenth century, more than twenty-five different prime meridians were in use around the world, including Paris, Beijing, Greenwich, Washington, and the location traditional in Europe since Ptolemy, the Canary Islands. Charles Withers explains how the choice of Greenwich to mark 0° longitude solved complex problems of global measurement that had engaged geographers, astronomers, and mariners since ancient times.

Withers guides readers through the navigation and astronomy associated with diverse meridians and explains the problems that these cartographic lines both solved and created. He shows that as science and commerce became more global and as railway and telegraph networks tied the world closer together, the multiplicity of prime meridians led to ever greater confusion in the coordination of time and the geographical division of space. After a series of international scientific meetings, notably the 1884 International Meridian Conference in Washington, DC, Greenwich emerged as the most pragmatic choice for a global prime meridian, though not unanimously or without acrimony. Even after 1884, other prime meridians remained in use for decades.

As Zero Degrees shows, geographies of the prime meridian are a testament to the power of maps, the challenges of accurate measurement on a global scale, and the role of scientific authority in creating the modern world.

"[A] wonderful new book on the long and uneven history of the Prime Meridian…The book is deeply and impeccably researched, and immensely detailed, but it is always a fascinating and compelling read…It is hard to imagine a better, fuller or more coherent account of how modern time came to be." - Journal of British Studies

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[A] compelling book…Withers manages to turn what might have been an obscure, rather technical topic into a fascinating account of international rivalry and a meditation on what the whole business of measuring the world around us can reveal about broader
cultural patterns.

"An extremely well researched book that ties together various disciplines and fills in details absent from previous single works on the subject…[Zero Degrees] will serve libraries, scholars, and researchers well for a longtime to come." - Journal of Historical Geography

"This is a delightful and thoughtful book…As an artifact, it is also beautifully produced by its publisher." - Bulletin of the Pacific Circle