WMAP (Wilkinson Microwave Anisotropy Probe) is a NASA Explorer-Class mission measuring the temperature of the cosmic background radiation over the full sky to spatial accuracy sufficient to significantly improve understanding of the nature of the origin, structure and fate of the Universe. The originally-named MAP probe was launched into a highly elongated orbit on June 30, 2001 aboard a Delta II-7425-10 (no. 286) . It spent several months in a parking orbit being checked out and then employed gravity assist from the Moon to reach a point in space 1.5 million km from Earth in the direction opposite the Sun on October 1. This point is known as the L2 point in space, or a Lagrangian Point, which is a quasi-stable node in the combined gravitational fields of the Earth, Moon and Sun.
In February 2003, the renamed WMAP program issued a "First Data Release" based on the initial full sky scan performed by the probe. Those data are archived and distributed via NASA's new Legacy Archive for Microwave Background Data Analysis (LAMBDA). The WMAP mission reveals conditions as they existed in the early universe by measuring the properties of the cosmic microwave background radiation over the full sky. Confirming and extending the observations of COBE, Boomerang and other cosmic background projects, WMAP identified the "anisotropic" or unequal spatial character of this radiation, and greatly extended our understanding of the nature of this radiation and of many of the fundamental cosmic parameters that are involved in its appearance. This microwave radiation was released approximately 380,000 years after the birth of the universe. WMAP creates a picture of the distribuiton of microwave radiation using temperature differences measured from opposite directions in the sky. The content of this image -- the nature and size distribution of the temperature variations -- tells us much about the fundamental structure of the universe.
[Adapted from the WMAP website maintained at the Goddard Space Flight Center]