From Cornell University Library: Tsar Bomba ("King Bomb" in Russian) is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detected. Developed by the Soviet Union, the bomb was originally designed to have a yield of about 100 megatons of TNT. However, the bomb yield was reduced to 50 megatons to reduce nuclear fallout. The attempt was successful, as it was one of the cleanest nuclear bombs ever detonated. Only one bomb of this type was ever built and it was tested on October 30, 1961, in the Novaya Zemlya archipeloago. Weighing 27 tons, the bomb was so large (26 ft long and 6.6 ft in diameter) that the bomber that carried it had to have its bomb bay doors and fuselage fuel tanks removed. The bomb was attached to a 1,760-lb. fall-retardation parachute, which gave the release and observer planes time to fly about 28 miles from ground zero. The fireball, about 5 miles in diameter, was prevented from touching the ground by the shockwave, but nearly reached the 6.5 mile altitude of the deploying bomber.
* Summary (from wired.com): @
* Summary and videos (from nuclearweaponarchive.org): @
* "Moscow's Biggest Bomb" (from Cold War International History Project, page 3): @
* Map of blast site (from Corbis Images): @