Hubble Deep Fields
One of the main scientific justifications for building Hubble was to measure the size and age of the Universe and test theories about its origin. Images of faint galaxies give 'fossil' clues as to how the Universe looked in the remote past and how it may have evolved with time. The Deep Fields gave astronomers the first really clear look back to the time when galaxies were forming. The first deep fields – Hubble Deep Field North and South – gave astronomers a peephole to the ancient Universe for the first time, and caused a real revolution in modern astronomy. Subsequent deep imagery from Hubble, including the Hubble Ultra Deep Field , has revealed the most distant galaxies ever observed . Because of the time it has taken their light to reach us, we see some of these galaxies as they were just half a billion years after the Big Bang. http://www.spacetelescope.org/science/deep_fields/ Video