![]() See a mathematical derivation of the Doppler shift equation. If the relative velocity between the emitting source and the observer was close to the speed of light, we would have to take relativistic effects into account thus, the equation would change. Notice that the region where an observer perceives an increase in the frequency of light is referred to as "blueshifted", and the region where the observer would perceive a lower frequency (on the left in the diagram) is referred to as "redshifted." And, it is important to note that the equations derived for the Doppler shift of sound work equally well for moving light sources provided the light sources are not moving near the speed of light. You will recognize this as a similar diagram to the one showing a fire truck approaching the stationary observer, except now the source is emitting light instead of sound. Illustration of light waves from a moving light source. The following diagram illustrates this phenomenon: It turns out that light from any part of the electromagnetic spectrum can be shifted up or down in frequency depending upon your relative motion to the emitting source. ![]() However, the police officer might then give you a ticket for speeding. If the Doppler shift also works for light then it must be possible to move so quickly towards a red traffic light that it would appear green to you! You might find it clever to use this argument if you get stopped for running a red light. ![]() Think about the spectrum of visible light: red-orange-yellow-green-blue-indigo-violet (or ROY G. How does this affect the spectra of distant objects in the Universe? Does light experience the Doppler shift? if the source is moving towards (negative velocity) the observed frequency is higher and the wavelength is shorter (blueshifted). ![]()
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