the velocity of the moving source. The energy shift resulting from a moving
source in comparison with the stationary source is referred to as the Doppler
shift and the following conditions apply:
• When the source is moving toward the observer, the measured photon
energy increases and the wavelength decreases (blue Doppler shift).
• When the source is moving away from the observer, the measured photon
energy decreases and the wavelength increases (red Doppler shift).