The Hubble Ultra Deep Field is an image of a small region of space in the constellation Fornax, composited from Hubble Space Telescope data accumulated over a period from September 24, 2003 through to January 16, 2004. It is the deepest image of the universe ever taken, looking back approximately 13 billion years, and it will be used to search for galaxies that existed between 400 and 800 million years after the Big Bang. The image contains an estimated 10000 galaxies.