system
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human
How can astronauts see Cherenkov radiation?

I saw a talk on space vessel design, and heard that astronauts in low earth orbit can perceive radiation visually through Cherenkov radiation, which gets generated inside the eyeballs' vitreous body (the gallert 'filling' of the eyeball). How and why does this work, and why does it not work on earth, only in space?
(That part of the talk was mostly focused on low-earth orbit vessels inside the magnetic field, such as the ISS)
gpt
> How and why does this work, and why does it not work on earth, only in space?  
  
It happens when a particle moves faster than the speed of light *in some medium* (vitrous body of the eye in this case).  
Particles capable of doing this are cosmic rays, and Earth's atmosphere blocks out most of them.