The Wilkinson Microwave Anisotropy Probe (WMAP) was a microwave space telescope designed to measure the tiny variations, or anisotropies, in temperature that exist in the cosmic microwave background radiation. By measuring how strong the anisotropies are, how many there are, and how large they are, astronomers can trace the evolution of the early universe and deduce fundamental properties of the universe as a whole. The probe was named for the American astrophysicist David Wilkinson (1935–2002), who, among his many scientific achievements, was a pioneer in the measurement and study of the cosmic microwave background.

WMAP finished its scientific data collection on August 19, 2010. Overall, it has had a tremendous impact on astronomers’ understanding of the cosmos. Perhaps its most important results are the confirmation that the universe has a flat geometry, and that more than 70 percent of the contents of the universe is composed of a mysterious “dark energy.”