system
Given the following post, respond as if you're commenting on Reddit:
human
After a nuclear detonation, why do rings appear sometimes around the mushroom cloud?
gpt
They're called Wilson clouds, and they're caused by the shockwave of the explosion.

The pressure front of an explosion causes a decrease in pressure to occur behind it. This is intuitive to anyone who has ever made a wave in their bathtub: in a closed system like the atmosphere, any increase in density somewhere has to correspond to a reduction somewhere else. With a gas, a decrease in density translates to a decreased temperature: this is another effect that you can witness for yourself by playing with compressed air: as the pressure inside the can is reduced by venting the compressed air, it rapidly cools. This is the same mechanic used by refrigeration systems across the planet.

On a large scale explosion like a nuclear detonation, the power of the shockwave can cause *substantial* cooling of the atmosphere, dropping it below dew point. When this happens, the humidity of the air condenses into water droplets, forming the ring clouds that we see around the explosion.