Doppler Effect This animation shows the difference in frequency of light sources that are moving toward or away from the detector in the center. Every five time periods, the sources emit a new (red) wave front. After emission, the wave fronts travel toward the detector at the speed of light, c = 4 pixels per time period. Meanwhile the speed of the sources is +/- 0.5 c at the start of the program or whatever the user changes it to with the slider at the left. Of course, when the source is traveling toward the detector at a significant fraction of c, the wave front spacing is compressed and when traveling away the wave front, spacing is expanded. The output of the detector in the center is the frequency difference of the waves it is currently receiving divided by the average frequency. Please press the "Click for equations" button for comments on the equations that define the results of this animation. The equations in the link below need to be very slightly modified for speeds close to the speed of light. The modification is 1/gamma=sqrt(1-v^2/c^2). This Doppler frequency shift is actually important in GPS satellites even when their velocity is perpencicular to our line of sight and their speed is only about 0.00001 that of light. See the second link for information on this effect.
Click Here for Doppler Frequency Equations
Click Here for Relativistic Doppler Frequency Equations
beta betaD Single Step Source Moves Detector Moves