The dull blue light glowing in the water might remind you of the tesseract when Howard Stark finds it underwater. But it’s actually just electromagnetic radiation. A special kind at that one. This kind of electromagnetic radiation is known as Cherenkov’s radiation.

What causes Cherenkov radiation?

Every charged particle has an electric field. The electric field travels at a speed of light. In water, for example, if the particle (mostly an electron) is accelerated to a speed that is more than the speed of light in water (cuz light gets a little bit slow in water), then the particle can, in a way, leave its electric field behind. And in doing so they disturb the electromagnetic fields. Or simply put, this speeding charged electron excites the electrons of water.

What causes the blue light in Cherenkov radiation?

In Cherenkov radiation, this electric field manifests as a shock front in the form of light. It excites atoms in the water as it tries to catch up with the particle. When these atoms are de-excited, they emit blue light. Simple and mind-blowing!

Is Cherenkov radiation harmful to humans?

Yes. These radiations are emitted near nuclear fission reactors. How many sci-fi movies do you have to see to realize that it’s really not safe to stand around a nuclear reactor? In all seriousness though, if you are safely enclosed and are observing the lights from a respectable distance and with safety precautions. You’ll be just fine.