Tsar Bomba (Russian: Царь-бомба; “Tsar Bomb”) is the nickname for the AN602 hydrogen bomb, the most powerful nuclear weapon ever detonated.

Its October 30, 1961 test remains the most powerful artificial explosion in human history.

The Tsar Bomba detonated at 11:32 on October 30, 1961, over the Mityushikha Bay nuclear testing range (Sukhoy Nos Zone C), north of the Arctic Circle over the Novaya Zemlya archipelago in the Arctic Sea.

The Tsar Bomba was a three-stage Teller–Ulam design hydrogen bomb with a yield of 50 to 58 megatons of TNT (210 to 240 PJ).

This is equivalent to 1,400 times the combined power of the bombs that destroyed Hiroshima and Nagasaki, 10 times the combined power of all the conventional explosives used in World War II, or one quarter of the estimated yield of the 1883 eruption of Krakatoa, and 10% of the combined yield of all nuclear tests to date.

So how big was the resulting mushroom cloud, anyways?

Answer: 64 kilometers (40 miles) high. That’s seven times the height of Mount Everest.

Ultimately, Tsar Bomba was never deployed into the Soviet Union’s arsenal for the simple reason that properly armed and detonated it would create fallout as much as 25 percent of all fallout emitted “since the invention of nuclear weapons”. Also, any bomber and crew delivering it would have no chance to escape the blast.

Why so big a bomb in the first place, though?

Other than the obvious reason (Russians have never been known to half-ass anything), there was the practical reason that due to the imprecision of delivery mechanisms and the uncertainty of the precise location of enemy installations, making a bomb this big meant a much higher chance of destroying the target.

There was, as well, a teensy additional problem – the blast was so monstrous that most of the explosion went up rather than out, meaning there was real risk of the fallout ultimately doing more harm to the country firing it.

(For the curious, the modern solution to this is to utilize multiple smaller warheads to essentially carpet an area with detonations.)

Via Wikipedia.