Cosmic and galactic microwave background, whole sky projection from the WMAP (Wilkinson Microwave Anisotropy Probe) satellite. The Milky Way galaxy is the red band crossing the sky, while the cosmic microwave background (CMB) fills the rest of the sky. The colours show tiny temperature variations (plus or minus 200 millionths of a Kelvin) in the background radiation (average is 3 Kelvin). The temperature varies from dark blue (cool) through blue, green and yellow to red (hot). The CMB is radiation from 380,000 years after the universe was created, that has cooled as the universe has expanded. The temperature variation is equivalent to changes in density in the early universe, and denser regions (red and yellow) eventually formed galaxies. Data obtained between 2003 and 2006.