When an object moves away from us, its light waves are stretched into lower frequencies or longer wavelengths, and we say that the light is redshifted.
Some redshifts are an example of the Doppler effect, familiar in the change in the apparent pitches of sirens and frequency of the sound waves emitted by speeding vehicles.
Another kind of redshift is cosmological redshift, which is due to the expansion of the universe, and sufficiently distant light sources (generally more than a few million light years away) show redshift corresponding to the rate of increase in their distance from Earth.
Finally, gravitational redshift is a relativistic effect observed in electromagnetic radiation moving out of gravitational fields.
The Red Shift supports the big bang theory, which states that the universe began from a very small initial point and then expanded from that point to give us the universe we see today.
Red Shift also supports the theory that the universe in expanding and it does so in an escalating manner.
The light from distant galaxies is red shifted (this tells us the galaxies are moving away from us) and the further away the galaxy, the greater the red shift (this tells us that the more distant the galaxy the faster it is moving).
Pictures: The visible spectra and Red Shift in cosmology.
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