Named for the Russian physicist Pavel Alekseyevich Cherenkov, Cherenkov radiation is emitted by any particle travelling faster than the speed of light in the medium in which it is travelling. As it collides with particles, it slows down and the lost kinetic energy is released in the form of photons. When the particle slows down enough to be travelling at exactly the speed of light in the medium, it emits an optical boom, exactly analogous to the sonic boom emited by an object passing the speed of sound in its medium.

This radiation is emitted in a forward cone, and can be seen with the naked eye (as a blue glow) if there are enough particles creating it. The Cherenkov radiation emitted by even a single such particle can be detected by devices such as photomultiplier tubes, and is crucial for measurements made at neutrino observatories, such as SNO.