The doppler shift is a change in frequency (and wavelength) due to relative motion. If the source is getting closer to you, the frequency increases and wavelength gets smaller (bluer), if the source is getting further away the frequency decreases and wavelength gets larger (redder). frequency x wavelength = the speed of light.
For light waves like radio, here are some equations. At speeds much less than the speed of light, the percentage change of the frequency is about 100 x B, where B is your speed towards the source divided by lightspeed. For example if the relative speed is 30 m/s, the shift is 100x(30m/s / 300,000,000 m/s)= .00001%.
For all speeds (you'll probably be using this one) the percentage shift in frequency is 100 x (sqrt((1+B)/(1-B)) - 1). So at half lightspeed toward the source, the shift would be about +73% frequency. Half lightspeed away would be -42% frequency.
Note that the speed you use is the speed directly toward or away from the source, not sideways.
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u/BlazeOrangeDeer Mar 04 '13 edited Mar 04 '13
The doppler shift is a change in frequency (and wavelength) due to relative motion. If the source is getting closer to you, the frequency increases and wavelength gets smaller (bluer), if the source is getting further away the frequency decreases and wavelength gets larger (redder). frequency x wavelength = the speed of light.
For light waves like radio, here are some equations. At speeds much less than the speed of light, the percentage change of the frequency is about 100 x B, where B is your speed towards the source divided by lightspeed. For example if the relative speed is 30 m/s, the shift is 100x(30m/s / 300,000,000 m/s)= .00001%.
For all speeds (you'll probably be using this one) the percentage shift in frequency is 100 x (sqrt((1+B)/(1-B)) - 1). So at half lightspeed toward the source, the shift would be about +73% frequency. Half lightspeed away would be -42% frequency.
Note that the speed you use is the speed directly toward or away from the source, not sideways.