COBE first measured the cosmic microwave background’s tiny temperature variations across the sky.
NASA launched the Cosmic Background Explorer, or COBE, on November 18, 1989. Its instruments measured the spectrum and anisotropies of the cosmic microwave background, the faint radiation left from the early universe.
COBE found that the background radiation has an almost perfect blackbody spectrum at about 2.725 kelvins. Its Differential Microwave Radiometer also detected tiny variations that traced the seeds of later cosmic structure.
George Smoot and John Mather received the 2006 Nobel Prize in Physics for work connected with COBE’s measurements. WMAP and Planck later mapped the background with substantially greater detail and resolution.