Red-Shift
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 Doppler shift made for enormous advances in astronomy. Astronomer Vesto Melvin Slipher was the first to do it. He had made several photographs of the Andromeda nebula in 1912. Analysis of the spectrum showed the wavelengths were shifted toward the blue end of the spectrum, indicating the nebula was approaching. Two years later, the analysis of the spectrum of 14 other spiral nebulae showed only two were blue-shifted, the other 12 were red-shifted. The red-shifts he observed for some spirals implied enormous speeds. This helped to prove that the spirals were galaxies outside of our own, and that the universe was far more vast than previously thought.
In 1929 Edwin Powell Hubble established a relationship between the radial velocity of a galaxy and its distance. It made it possible to relate a galaxy's distance with the amount of red-shift its light showed. The farther out into space he looked, the greater the light was shifted toward the red. In fact, the more distant an object was, the faster it was rushing away from us. His colleague, Milton Humason (1891-1972), analyzed the red-shift of these distant galaxies and found that some were moving away at nearly one-seventh the speed of light.
The discovery that galaxies were moving away at tremendous rates of speed had enormous implications. It implied that the universe was expanding at a phenomenal rate, supporting George Henri Lemaître 's version of Albert Einstein's theory of relativity. The cause of the expansion might have been a cataclysmic explosion that had occurred billions of years in the past, a concept something that astronomers refer to as the big bang theory.
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