The Hubble Deep Field is a region of the northern celestial hemisphere about one 30-millionth the area of the sky that contains at least 1,500 faint galaxies.

The region was imaged by NASA's Hubble Space Telescope in 1995 and is equivalent in apparent size to a shirt button held 75 feet away. The region is so small that only a few foreground stars from the Milky Way are visible in the image. If the Hubble Deep Field is typical of the rest of space, then it can be extrapolated that there are hundreds of billions of galaxies, each containing billions of stars within the visible universe alone.

The image was assembled from many separate exposures (342 frames total were taken) with the Wide Field and Planetary Camera 2 for ten consecutive days between December 18 and 28, 1995.

Three years later, a region in the south celestial hemisphere was imaged in a similar way and yielded similar pictures. It was dubbed Hubble Deep Field South. The similarities between the two regions strengthened the belief that the Universe is uniform over large scales and that Earth occupies a typical region in the Universe. The original Hubble Deep Field has been retrospectively renamed the Hubble Deep Field North by some.

from Wikipedia