When a particle travels faster than the speed of light in a medium itemits Cerenkov radiation. When light is observed traveling in a vacuumit is always seen to have a speed of 3x108 m/s, this velocity islower, however, when light travels through a medium such as glass, air, orwater. The new speed of light is given by c/n where n is theindex of refraction in that medium. Air has an index of refraction of 1.0003at sea level. The speed of light at sea level is then 2.9991x108m/s. When an electron or other charged particle passes through the atmospherefaster than this it will generate an electromagnetic shock wave. This shcokwave is the equivalent of a sonic boom emitted by a supersonic plane.