Those bombs, the only nukes that have ever been used in war, helped bring an end to World War II, with Japan surrendering on Aug. 15. They also allowed U.S. troops to avoid what would have likely been a deadly ground invasion of Japan. But that victory came at a great toll to humanity.
Alex Wellerstein, a nuclear historian at the Stevens Institute of Technology, created a NukeMap that allows you to visualize what the Hiroshima and Nagasaki explosions would look like in your hometown. Kuang Keng Kuek Ser at Public Radio International has also developed a version, using slightly different estimates.
Here is what Little Boy, the Hiroshima bomb, would look like on Wellerstein's map if detonated in Washington, D.C. An explanation of what the colors mean is below.
The effects of a nuclear bomb depend a lot on the height of the detonation. Little Boy, a 15 kiloton bomb, was detonated higher in the air, increasing the size of its effects.
As the key below shows, the area within the central yellow ring would be the maximum size of the nuclear fireball. The red ring shows the air blast radius, in which the pressure from the bomb is intense enough to severely damage or demolish heavily built concrete buildings, and fatalities approach 100 percent.
The green ring shows the radiation radius. Without medical treatment, 50 to 90 percent of people within that circle will die from the acute affects of radiationalone, either within several hours or several weeks. The gray circle shows the air blast radius, in which pressure is high enough to knock over most residential buildings. Injuries are universal and fatalities are widespread, says Wellerstein.
Finally, the yellow circle shows the thermal radiation radius. People within this circle would sustain third degree burns, which can cause severe scarring or disablement, and can require amputation.
Wellerstein says those who are out in the open would fare far worse than those inside buildings. But either way, the resulting scene would be absolutely horrific.
Here's what the Hiroshima explosion would look like if it hit New York City, using the same key as above. Most of lower Manhattan would likely be devastated.
As Wellerstein's map shows, the bomb that hit Nagasaki, Fat Man, was actually even more destructive. That bomb was 20 kilotons, compared with 15 kilotons in Hiroshima. Here's what that would look like over New York City:
If as if that's not scary enough, weapons technologies have progressed a lot in the past 70 years.
The World War II weapons used fission, the process of splitting an atom. By the 1950s, the U.S. had figured out how to harness the power of fusion in bombs as well, making them much more powerful, Wellerstein says.
In more recent decades, we've focused on developing smaller weapons that are much more precise, but still destructive. "The idea here is that these bombs are maybe 20 times the power of Hiroshima, but are only the size of a trashcan," says Wellerstein.
Here's what a W-87, a 300-kiloton weapon that is currently in the U.S. arsenal, would look like if detonated over D.C.
Again, the green area is the radiation radius, and the yellow area is the nuclear fireball. The grey area is the air blast radius, which knocks down most residential buildings, and the yellow area is the thermal radiation radius, which results in third-degree burns as far as Mt. Rainer, Md., and Arlington, Va.
And here's what a 60-kiloton bomb, the size of the largest nuclear bomb that India claims to have tested in 1998, could do to New York. This time, the damage spreads well beyond Manhattan into Brooklyn and New Jersey.
These maps bring home the absolute horror of nuclear war, and the experience of hundreds of thousands of people in Hiroshima and Nagasaki 70 years ago.
In Wellerstein's description, the most terrifying aspect of Hiroshima was the chaos and confusion. People didn't realize at first that their city had been hit by a nuclear weapon. Most thought their house had been struck by a conventional bomb, and then gradually realized the devastation extended to the whole city.
Many people died due to secondary fires that started when bomb destroyed houses and knocked over stoves. Others started feeling sick, vomiting, having miscarriages and eventually dying due to radiation poisoning, without really understanding what was happening to them.
Japanese soldiers were slow to arrive, and couldn't do much once they got there. Many people made their way to hospitals, only to find the building destroyed or the doctors sick or dead.
“It truly was a vision of hell,” a woman who saw the bombing as a little girl recalled.