Chet Raymo is simply the best literary naturalist writing today, producing elegantly written, insightful books that open from a seemingly modest premise into a dizzying (and sometimes humbling) view of our place in the universe. Recently retired from teaching astronomy in Massachusetts, Raymo has lately been producing a perfect little book every year or so. His latest, Walking Zero: Discovering Cosmic Space and Time Along the Prime Meridian, is brief, tightly written and told in the irresistible voice that Raymo has established as his trademark: literate, enthusiastic, alternately educational and lyrical. This time around, he begins by walking along much of the Prime Meridian (zero degree of longitude) in England. Raymo's route takes him near Newton's rooms at Cambridge, Darwin's home in Kent, even the area where Piltdown Man was found. He uses these geographical prompts to open up his story. He tells the fascinating tale of how a prime meridian was determined and why it was even necessary. He explores the broader view of the cosmos that emerged from Newton's work, and the greater context for human life that resulted from Darwin's. Raymo can't resist a quirky character or an entertaining anecdote. As he walks near Lyme Regis, for example, he tells the story of pioneer dinosaur researcher Mary Anning. Clad in the long skirts required in the early 19th century, she scoured the chalky cliffs for fossils, the sale of which supported her family. By doing so she helped change our whole view of the past. Some of Raymo's books, such as The Soul of the Night, are more lyrical and personal, emphasizing his way of connecting to the spiritual implications of natural history. However, even such straightforward science and history books as Walking Zero always manage to be more than they seem at first glance. Raymo is always interested in meaning, in the philosophical implications of scientific discovery. He is our apostle of the joy of curiosity, and Walking Zero shows him at his best. Michael Sims is the author of Adam's Navel and editor of The Annotated Archy and Mehitabel.