"The discovery of the Big Bang and the recession of the galaxies came from a commonplace of nature called the Doppler effect. ...An object approaching us at very high velocities is perceive to have the color of its spectral lines blue-shifted. An object receding from us at very high velocities has its spectral lines red-shifted. ...Following a lead by the astronomer V. M. Slipher... Humason and Hubble found, to their amazement, that the spectra of all distant galaxies are red-shifted."