A red-shift refers to the shifting of wavelengths of energy toward the red end of the color spectrum.

In 1842 Christian Johann Doppler determined that if a light source is moving toward or away from an observer, the wavelengths of the light will be shifted. If the light is coming toward the observer the wavelengths are shortened, and the light bunches up toward the blue end of the color spectrum. If the movement is away, the wavelengths are stretched out and the shift is toward the red end of the spectrum. This principle, known as the Doppler effect, also holds true for sound waves. Light is passed through a spectroscope, and a spectrum of the various elements can be observed. By comparing the spectrum of the object with that of known elements in the laboratory, a comparison between the spectra can be made and shifts detected.

Observing an object's...