© NASA, WMAP Science Team.
This map shows the pattern of temperature variations in the cosmic microwave background (CMB) measured with the WMAP satellite. WMAP made a differential measurement of the CMB temperature with two sensitive radio antennae mounted with a fixed displacement between them. As the satellite rotated, the radio antennae traced out temperature variations in the entire sky. The largest temperature differences (between the red and dark blue regions) are about 0.0004 K, and the characteristic angular size of the temperature variations is around 1 degree. By analyzing the detailed pattern in this map, WMAP scientists infer that less than 4 percent of the universe is ordinary matter, and 23 percent is dark matter. (Unit: 4)