These shifts in frequency are easily measured because the emmision? and absorbtion? patterns for molecules are distinctive. The amount of frequency shift can provide a means of measuring the relative speed between the source and the observer.
[Edwin Hubble]? was one of the primary researchers in this area of cosmology. It has been observed that the further away a galaxy is from us, the higher the relative speed away from us (greater redshift). Looking back in time, this suggests that all the matter in the universe originated from the same point. This has lead to the Big Bang theory.
Red Shift. is also a novel by Alan Garner.