Human shadows of Hiroshima: The haunting legacy of the atomic bomb

Exactly 79 years ago, on August 6, 1945, the United States dropped an atomic bomb on Hiroshima. A few days later, the same fate befell Nagasaki. After the atomic bombs were dropped on these Japanese cities, human shadows appeared on stairs, buildings, and sidewalks. The scientific service Live Science explains in detail how this phenomenon occurred.

One of the most recognizable examples is the outline of a human figure on the steps in front of the Sumitomo Bank branch in Hiroshima. The fragment of the steps with the visible outline, called the "human shadow of death," is currently located in the city's Peace Museum. The institution purchased this fragment in January 1971 when the shadow began to fade due to weather conditions.

Michael Hartshorne, a retired professor of radiology from the University of New Mexico, whom Live Science references, explains that after the atomic bomb exploded, intense light and heat spread from the point of implosion. People and objects encountered along the way absorbed the light and energy, causing the areas around them to be highly illuminated. This contrast made the shadows very visible.

In practice, this means that the "atomic shadows" reveal the actual colors of buildings and sidewalks before the explosion. Live Science highlights that the enormous amounts of energy released during the bomb's detonation result from the fission reaction of an atomic nucleus. The reaction occurs when a neutron strikes the heavy nucleus of an atom, such as the isotope Uranium-235 or Plutonium-239, causing it to split. This initial collision triggers a chain reaction until the fuel is depleted.

The United States dropped the atomic bomb on Hiroshima on August 6, 1945. The "Little Boy" bomb, weighing 8,800 lbs, killed an estimated 90,000 people, about 30% of the city's then-population.

Three days later, the "Fat Man" bomb was detonated over Nagasaki. Although it was more potent than its predecessor, it caused fewer casualties, killing between 40,000 to 70,000 people. The shockwave was partially weakened by a hill that surrounded one of Nagasaki's districts.

Interestingly, the second atomic bomb was initially intended to be dropped on the city of Kokura. The pilots were ordered to carry out the attack only with good visibility. Heavy cloud cover over Kokura made Nagasaki the target instead.

Additionally, Kokura was to be the backup target on August 6, 1945, in case of poor visibility over Hiroshima. In Japan, the terms "Kokura’s luck" and "Kokura’s lucky man" are used to describe situations where someone unknowingly avoids a great tragedy.