Today's interesting fact has to do with light.

Everyone knows that nothing can travel faster than light.

However, this is an incorrect statement of fact when light is in any medium other than a vacuum.

The speed of light in water, in an atmosphere or in glass or plastic is slower than it is in a vacuum.

Neutrinos and electrons are particles and Neutrinos don't slow down when they go through water, glass or even rock or metals.

When a particle does this, it generates Cherenkov radiation, which is an electromagnetic radiation that is emitted when a charged particle passes through a dielectric medium at a speed greater than the velocity of light in that medium.

This radiation has been likened to the sonic boom created by the sound wave produced when an aircraft exceeds the speed of sound.

In this case charged particles polarize the molecules of the medium, which then turn back rapidly to their ground state, which then emit radiation in the process.

The characteristic blue glow often seen in images of nuclear reactors is due to Cherenkov radiation in the dielectric medium of water