On July 9, 1962, crowds gathered on the beaches of Honolulu, Hawaii, and watched as the US detonated a nuclear bomb in outer space. 

Known as Starfish Prime, the explosion was part of a series of high-altitude nuclear tests known somewhat innocuously as "Operation Fishbowl". Five nuclear devices were set off during the tests, with Starfish being the largest at approximately 1.4 megatons (the equivalent in terms of energy discharge of 1.4 million tons of TNT being detonated all at once).

After the bomb was detonated some 400 kilometers (249 miles) above Johnston Island in the Pacific Ocean, and auroras were seen across the sky as electronics began to fail.

"At Kwaialein, 1400 miles to the west, a dense overcast extended the length of the eastern horizon to a height of 5 or 8 degrees," one eyewitness of the event said, as recorded in a military report. 

"At 0900 RC a brilliant white flash burned through the clouds rapidly changing to an expanding green ball of irradiance extending into the clear sky above the overcast. From its surface extruded great white fingers, resembling cirro-stratus clouds, which rose to 40 degrees above the horizon in sweeping arcs turning downward toward the poles and disappearing in seconds to be replaced by spectacular concentric cirrus like rings moving out from the blast at tremendous initial velocity, finally stopping when the outermost ring was 50 degrees overhead. "

"They did not disappear but persisted in a state of frozen stillness."

"As the greenish light turned to purple and began to fade at the point of burst, a bright red glow began to develop on the horizon at a direction 50 degrees north of east and simultaneously 50 degrees south of east expanding inward and upward until the whole eastern sky was a dull burning red semicircle 100 degrees north to south and halfway to the zenith obliterating some of the lesser stars. This condition, interspersed with tremendous white rainbows, persisted no less than seven minutes."

The test – almost certainly a response to similar Soviet tests – were designed in part to test the effect on the Earth's magnetic field, and whether nuclear explosions in space could be weaponized against the Soviets. They found, to their surprise, that it was effective at shutting down several satellites, including one launched the day after the test that were hit with higher than expected levels of radiation.

"Some electronic and electrical systems in the Hawaiian Islands, 1400 kilometers distant, were affected, causing the failure of street-lighting systems, tripping of circuit breakers, triggering of burglar alarms, and damage to a telecommunications relay facility," a report in 2012 noted. 

"What is significant about an EMP attack is that one or a few high-altitude nuclear detonations can produce EMP effects that can potentially disrupt or damage electronic and electrical systems over much of the United States, virtually simultaneously, at a time determined by an adversary."

The effects of the test – viewed in "rainbow parties" below – lasted longer than the pretty aurora. An artificial radiation belt was created by the blast, with levels higher than the naturally-occurring Van Allen belts, that lasted for several years.