For 10 points, name this effect in which the apparent frequency of waves is affected by the relative motion of the source and the observer.
This effect provides the cooling limit for low-density gases, such as rubidium-85, cooled with lasers in a technique named for it. A result of this effect is diminished by two lasers with the same frequency used to induce stimulated emission, a technique known as saturated absorption spectroscopy. An astronomer can calculate the radial velocity of stars by measuring how this effect blue-shifts or red-shifts their spectra. For 10 points, name this effect in which the apparent frequency of waves is affected by the relative motion of the source and the observer.
This effect provides the cooling limit for low-density gases, such as rubidium-85, cooled with lasers in a technique named for it.
Doppler effect [or Doppler shift; prompt on redshift or blueshift before read]