On this day in history - July 9th, 1962 - Starfish Prime detonates above Johnston Island.
Starfish Prime was a 1.4 megaton thermonuclear weapon, one of only five the United States tested in outer space. As part of operation Dominic, the United States wanted more information on exoatmospheric nuclear activity.
The Atomic Energy Commission knew the test would cause an electromagnetic pulse or EMP, but it didn't know how large it would be. Starfish Prime's EMP knocked out electrical equipment as far south as Honolulu, Hawaii.
The shot also caused auroras similar in color to the naturally occurring Auroras Borealis and Australis in the Northern and Southern Hemispheres.