Cherenkov Radiation
The characteristic blue optical shockwave radiation emitted when a charged particle travels through a dielectric medium faster than the phase velocity of light in that medium.
Governing formula
cos θ = c / (n v) = 1 / (n β)
SI unit
Blue Light Photons (~400 nm)
In depth
The electromagnetic analogue of a sonic boom. As a relativistic electron moves faster than c/n in water, it polarizes medium molecules along its path, generating a coherent shockwave cone of blue light at angle θ.
Examples in the real world
The eerie glowing blue light observed surrounding submerged nuclear reactor cores in water pools.