These images, called the Hubble Deep Field (HDF), were assembled from 342 separate exposures taken with the Wide Field and Planetary Camera 2 (WFPC2) of the Hubble Space Telescope between December 18 and 28, 1995. Representing a narrow “keyhole” view stretching to the visible horizon of the universe, the HDF images cover a speck of the sky only about the width of a dime located 75 feet away. Though the field is a very small sample of the heavens, it is considered representative of the typical distribution of galaxies in space because the universe, statistically, looks largely the same in all directions. Gazing into this small field, Hubble uncovered an assortment of at least 1,500 galaxies at various stages of evolution.

Most of the galaxies are so faint (nearly 30th magnitude or about four-billion times fainter than can be seen by the human eye) that they had never before been seen by even the largest telescopes. Some fraction of the galaxies in these pictures probably date back to nearly the beginning of the universe.

The term “deep” in an astronomical sense means looking at the faintest objects in the universe. Because the most distant objects are also among the dimmest, the HDF is the equivalent of using a “time machine” to look into the past to witness the early formation of galaxies, perhaps less than one billion years after the universe’s birth in the Big Bang.

The image data are so important, they were made available immediately after they were taken to astronomers around the world to pursue research on the formation of galaxies and for probing basic questions about the structure and evolution of the universe.

Adapted from a press release by the American Astronomical Society