Expansion of the Universe

Astronomer Vesto Slipher noticed that there are more galaxies going away from us than approaching us. This was observed by looking at the spectrum of its light. Similar to the Doppler effect on the wavelength (pitch) of sound waves when the source of the sound is moving towards and away. The same can be detected from light waves, this phenomena known as the Red Shift results when a source of light, in this case light from a distant galaxy, has a shift in color due to the distance and speed the object is moving away from sight. In the event of a train moving away from one self, the sound changes its pitch do to the sound-wave stretching to longer wavelength; similarly when a distant illuminating object moves away from us, the visible wavelength stretches to a longer wavelength resulting in the object looking a more reddish color. In 1929, Edwin Hubble discovered that farther galaxies are going away from us at higher speeds, proportional to their distance, in other words if the wavelength had doubled, space must have expanded by a factor of two. Using the red shift method scientists have calculated the approximate age of the universe by seeing that the separation between galaxies gets smaller going back from the expanding universe. This can be traced back to when the distance between galaxies was essentially zero. 

                                                                               http://map.gsfc.nasa.gov/universe/uni_expansion.html