Wilkinson Microwave Anisotropy Probe

https://map.gsfc.nasa.gov/news/5yr_release.html
NASA/WMAP Science Team
The cosmic microwave temperature fluctuations from the 5-year WMAP data seen over the full sky. The average temperature is 2.725 Kelvin (degrees above absolute zero; equivalent to -270 C or -455 F), and the colors represent the tiny temperature fluctuations, as in a weather map. Red regions are warmer and blue regions are colder by about 0.0002 degrees.
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