Relativistic Doppler Effect
(Note: This page is actively being eddited) The Relativistic Doppler Effect describes the alteration of the wavelength and frequency of light (Classical Doppler Effect) while accounting for the consequences of Special Relativity.
Classical Doppler Effect
Consider a police car that is speeding past you with its sirens on. Have you ever noticed that the pitch of the siren is higher as it approaches you, but drops as it diverges from you? The beginning of the audio correlates to the rightmost figure and progresses to the leftmost.