The Cosmic Background Explorer (COBE) satellite was launched 25 years ago on 18 September, 1989. It showed that the cosmic microwave background, the cold afterglow of the Big Bang, was not completely uniform. Tiny temperature fluctuations visible in this “map” have grown into enormous galactic structures in the intervening 14 billion years.
COBE made this “map of the early universe” showing tiny variations in the cosmic microwave background. NASA/GSFC