Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time is a 1995 best-selling book by Dava Sobel about John Harrison, an 18th-century clockmaker who created the first clock (chronometer) sufficiently accurate to be used to determine longitude at sea—an important development in navigation. The book was made into a television series entitled Longitude. In 1998, The Illustrated Longitude was published, supplementing the earlier text with 180 images of characters, events, instruments, maps and publications.

Dava Sobel is an American writer of popular expositions of scientific topics. Her books include Longitude, about English clockmaker John Harrison; Galileo's Daughter, about Galileo's daughter Maria Celeste; and The Glass Universe: How the Ladies of the Harvard Observatory Took the Measure of the Stars about the Harvard Computers.