Starfish Prime was successful. The Thor missile carried the test instrumentation and the W-49 warhead/Mk-4 RV payload to 248 miles. The test appeared quite spectacular from Hawaii (800 miles away) and at Kwajalein (1600 miles away), with impressive light displays from an artifical aurora lasting up to seven minutes. The electromagnetic pulse (EMP) from this test sent power line surges throughout Oahu, knocking out street lighting, blowing fuzes and circuit breakers, and triggering burglar alarms.

Source: nuclearweaponarchive.org

And for a story of what _not_ to do when testing a nuclear weapon, see:

en.wikipedia.org