Čerenkov radiation

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The Cherenkov effect is an effect in physics discovered by Pavel Alekseyevich Čerenkov.

[change] Theory

Whenever a particle with an electric charge moves faster than light in a medium, it sends out photons (light particles) and thereby loses energy.

[change] Explanation

Because nothing can move faster than light in vacuum, there is no Cherenkov light in vacuum. But, for example, in water, light moves only with 75% of the speed in vacuum. Here particles with very high energy can move faster and create Cherenkov light.

Because the Cherenkov effect is strongest for light with short wavelengths, Cherenkov light often appears blue.