Red Shift

An example of a red shift can be seen in the spectra of quasars, extremely powerful sources of radio and light waves. A series of bright spectral lines caused by hydrogen appears in the spectrum of Quasar 3C 273. The wavelength of each line of 3C 273 is 15.8 per cent longer than normal. Thus, the red shift of the quasar is 15.8 per cent. Most astronomers believe that red shifts occur in cosmic objects because the earth and the objects are speeding away from each other. The shift in wavelength is caused by the Doppler effect.

The amount of red shift of an object indicates its velocity. Objects with small red shifts move at a percentage of the speed of light equal to the red shift percentage. To calculate the velocity of objects that have larger red shifts, astronomers must take into account the effects of the special theory of relativity. The red shift of 3C 273 indicates a speed of 43,500 kilometres per second, which is 14.5 per cent of the speed of light. Some quasars have red shifts of more than 300 per cent, indicating that they have a speed of over 88 per cent of the speed of light.

In 1929, Edwin Hubble, an American astronomer, discovered that the red shift of galaxies increases uniformly with the increasing distance of the galaxies from the earth. Thus, the red shift could be used to estimate the distance of the galaxies from the earth. Hubble's discovery has led astronomers to believe that galaxies are rapidly moving away from one another as in an explosion. His findings form the basis for the theory that the universe is expanding.