There is no single accepted definition of "fireball" like the Kármán line where outer space begins, and even that is just a convention. The "artificial sun" cr

There is no single accepted definition of "fireball" like the Kármán line where outer space begins, and even that is just a convention. The "artificial sun" created at Hiroshima, the early-stage plasma fireball at 1 ms, is estimated to have been 5 to 10 meters across.