Fireball

A primary means by which the energy is delivered from a nuclear explosion to an object is by thermal radiation.

Within less than one millionth of one second from the detonation of the weapon, a fireball is formed. This fireball is an extremely hot and highly luminous spherical mass of air and gaseous weapon residues. Temperatures of a nuclear explosion are equal to the interior of the sun, about 100,000,000° Celsius.