The Event at 8:16am on August 6th 1945 in Hiroshima, Japan
On August 6, 1945, the United States dropped an atomic bomb on the city of Hiroshima. The bomb was known as "Little Boy", a uranium gun-type bomb that exploded with about thirteen kilotons of force. At the time of the bombing, Hiroshima was home to 280,000-290,000 civilians as well as 43,000 soldiers. Between 90,000 and 166,000 people are believed to have died from the bomb in the four-month period following the explosion. The U.S. Department of Energy has estimated that after five years there were perhaps 200,000 or more fatalities as a result of the bombing, while the city of Hiroshima has estimated that 237,000 people were killed directly or indirectly by the bomb's effects, including burns, radiation sickness, and cancer.


0916:02 (8:16:02 AM Hiroshima time): After falling nearly six miles in forty-three seconds, Little Boy explodes 1,968 feet above the Dr. Shima’s Clinic, 550 feet away from the aiming point of the Aioi Bridge. Nuclear fission begins in 0.15 microseconds with a single neutron, initiating a supercritical chain reaction that increases the temperature to several million degrees Fahrenheit hotter than the surface of the sun at the time the bomb casing blows apart. The yield is 12.5-18 Kt (best estimate is 15 Kt). 
It is the peak of the morning rush hour in Hiroshima. Above the city, the fireball is rapidly expanding. 

.1 seconds: The fireball has expanded to one hundred feet in diameter combined with a temperature of 500,000°F. Neutrons and gamma rays reach the ground. The ionizing radiation is responsible for causing the majority of the radiological damage to all exposed humans, animals and other biological organisms.
.15 seconds: The superheated air above the ground glows. A woman sitting on steps on the bank of the Ota river, a half a mile away from ground zero, instantly vaporizes.
0.2-0.3 seconds: Intense infrared energy is released and instantly burns exposed skin for miles in every direction. Building roofing tiles fuse together. A bronze Buddha statue melts, and even granite stones. Roof tiles fuse together, wooden telephone poles carbonize and become charcoal-like. The soft internal organs (viscera) of humans and animals are evaporated. The blast wave propagates outward at two miles per second or 7,200 miles per hour.
1.0 second and beyond: The fireball reaches its maximum size, approximately 900 feet in diameter. The blast wave slows to approximately the speed of sound (768 miles per hour). The temperature at ground level directly beneath the blast (hypocenter) is at 7,000° F. The mushroom cloud begins to form.
The blast wave spreads fire outward in all directions at 984 miles per hour and tears and scorches the clothing off every person in its path. The blast wave hits the mountains surrounding Hiroshima and rebounds back. Approximately 60,000 out of the city's 90,000 buildings are demolished by the intense wind and firestorm.
Approximately 525 feet southwest from the hypocenter, the copper cladding covering the dome of the Industrial Products Display Hall is gone, exposing the skeleton-like girder structure of the dome. However, most of the brick and stonework of the building remains in place.
The ground within the hypocenter cools to 5,400°F. The mushroom cloud reaches a height of approximately 2,500 feet. Shards of glass from shattered windows are imbedded everywhere, even in concrete walls. The fireball begins to dim but still retains a luminosity equivalent to ten times that of the sun at a distance of 5.5 miles.
Nuclear shadows appear for the first time as a result of the extreme thermal radiation. These shadows are outlines of humans and objects that blocked the thermal radiation. Examples are the woman who was sitting on the stairs near the bank of the Ota River. Only the shadow of where she sat remains in the concrete. The shadow of a man pulling a cart across the street is all that remains in the asphalt. The shadow of a steel valve wheel appears on a concrete wall directly behind it because the thermal radiation was blocked by the outline of the wheel.
Russell Gackenbach, the navigator aboard Necessary Evil, at a distance of 15 miles from the atomic blast, is illuminated by light so bright that, even with his protective goggles on, he could have read the fine print of his pocket Bible.
On the ground, the firestorm continues to rage within an area which had now grown to over a mile wide. A gruesome, raging red and purple mass begins to rise in the sky. The mushroom column sucks superheated air, which sets fire to everything combustible. Bob Caron likens the sight to "a peep into Hell.”
A coded message drafted by Parsons is sent to General Thomas Farrell at Tinian. It stated: “Clear cut, successful in all aspects. Visible effects greater than Alamogordo. Conditions normal in airplane following delivery. Proceeding to base."
Enola Gay circles Hiroshima a total of three times beginning at 29,200 feet and climbing towards 60,000 feet before heading for home. It was 368 miles from Hiroshima before Caron reported that the mushroom cloud was no longer visible. 

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