A new documentary by Russia’s state atomic agency offers newly declassified footage of the biggest thermonuclear bomb of all time. ‘Tsar Bomba,’ which the Soviet Union tested in 1961, was so powerful that people saw the flash from up to 630 miles away, reported popular mechanics. The Soviets only tested the bomb once, a symbol of their technology and military power before an international treaty prohibited further tests. Although tens of thousands of nuclear weapons still exist, none is even remotely as powerful as the great and terrible Tsar Bomba, reported popular mechanics. Watch the video to know more.