A tight-knit, high-powered group of scientists and engineers spent eight years building a satellite designed, in effect, to take a fingerprint of the universe. Launched in 2001, the Wilkinson Microwave Anisotropy Probe (WMAP) reported its first results two years later with a set of brilliant observations that added focus, detail, and insight to our formerly fuzzy view of the cosmos. Michael Lemonick, who had exclusive access to the researchers as WMAP gathered its data on the microwave afterglow of the Big Bang, here tells the full story of WMAP and describes its revelations. This book is both a personal and a scientific tale of discovery. In its pages, readers will come to know the science of cosmology and the people who, seventy-five years after we first learned that the universe is expanding, deciphered some of its deepest mysteries in the patterns of its oldest light.