CHAPTER 7
After about 0.1 millisecond (one ten-thousandth part of a second) has elapsed, the radius of the ball of fire is some 45 feet, and the temperature is then in the vicinity of 300,000 degrees Centigrade. At this instant, the luminosity, as observed at a distance of 100,000 yards (5.7 miles), is approximately 100 times that of the sun as seen at the earth's surface ... the ball of fire expands very rapidly to its maximum radius of 450 feet within less than a second from the explosion.
—Los Alamos