First-handand forensicreveal the colossal impact of the biggest man-made blast, detonated by the Soviets some 50 years ago. In theory, the bomb had a maximum yield of 100 megatons if it were to have included a U-238 tamper. The Tsar Bomba mushroom cloud seen from a distance of 161 km (100 miles). The crown of the cloud is 56 km (35 miles) high