Result of the relative motion of the light emitting object and the observer. If the source of light is moving away, the Distance from one peak of a wave to the next. Wavelength is measured in units of distance. The wavelengths of visible light correspond to ~400-650 nm. Wavelength is an important way to characterize a wave. For light, the shorter the wavelength, the higher the energy of the light wave. of the light is stretched (shifted towards lower frequencies). If the source of light is approaching, the wavelength of the light is compressed (shifted towards higher frequencies). These effects, called redshift and blueshift, respectively, are together known as Doppler shifts. The shift in the wavelength, λobserved – λrest, is given by a simple formula (v = velocity, c = Speed at which electromagnetic radiation propagates in a vacuum. Although referred to as the speed of light, this should be more properly called the 'speed of a massless particle’ as it is the speed at which all particles of zero mass (not only photons, but gravitons and massless neutrinos if):
Some or all content above used with permission from J. H. Wittke.