Wikipedia:POTD column/April 25, 2006

The Hubble Ultra Deep Field or HUDF is an image of a small region of space composited from Hubble Space Telescope data accumulated over a period from September 3, 2003 through January 16, 2004. It is the deepest image of the universe ever taken in visible light, looking back in time more than 13 billion years. The HUDF contains an estimated 10,000 galaxies. The patch of sky in which the galaxies reside (just one-tenth the diameter of the full moon) was chosen because of the low density of bright stars. Although most of the targets visible in the Hubble image can also be seen at infrared wavelengths by ground-based telescopes, Hubble is the only instrument which can make observations of these distant targets at visible wavelengths.
Photo credit: NASA
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