Cherenkov radiation (P.A. Cherenkov): The radiation emitted by a huge particle which is moving faster than light in the medium via which it is travelling. No particle can travel faster than the light in vacuum, however the speed of light in other media, like water, glass, and so forth, are considerably lower. Cherenkov radiation is an electromagnetic analogue of the sonic boom, however Cherenkov radiation is the shockwave set up in an electromagnetic field.