This colorful display shows tiny differences (or "anisotropies") in the cosmic microwave background over the entire sky. The average temperature is just 2.73 kelvins (2.73 degrees Celsius above absolute zero), and the temperature differences represented here span mere millionths of a degree. Red represents the warmest locations, while blue reveals the coldest spots. These tiny temperature variations map the structure of the early universe.
NASA / WMAP Science Team