![Supercavitation](http://d38zjy0x98992m.cloudfront.net/2949b4c0-8abe-43ba-8cc0-d79d905ff912/SUPERCAVITATION_UHD_xlarge.jpg)
Doppler Shift (General)
Generalised animation of the increase in frequency observed in waves emitted from an approaching source (or conversely a decrease in frequency in waves emitted from a receding source). This Doppler Shift happens in sound waves (e.g. a siren of an approaching emergency vehicle or the change in pitch of a passing car engine) and in light waves (the red Doppler shift of a receding star or the blue Doppler shift of an approaching star, redshift and blueshift).
This animation uses a ball as the wave source. As the ball moves from left to right it emits wave-fronts that continue to radiate out from their position of origin. The ball moves on and creates a new point of origin for the next wavefront and so on. In this way, the waves bunch together at the front of the ball and spread out behind. Similar to a jet plane approaching the speed of sound and radiating sound waves. In the case of light waves then the higher frequency at the front yields a bluer light (blue shift), while behind the light source (e.g. a star) the light is stretched out, lengthening the frequency, creating a redshift.
![MACH 2 Doppler Effect at Twice the Speed of Sound (or Ship's Bow Wave)](http://d38zjy0x98992m.cloudfront.net/dbf664b4-cfde-4309-8574-75023c2ae1f5/MACH_Two_UHD_xlarge.jpg)