Astronomers pointed a telescope at 'nothing' for ten days and found 3,000 galaxies

In 1995, Robert Williams aimed the Hubble Space Telescope at a patch of sky near the Big Dipper that looked completely empty to the naked eye, leaving the shutter open for over 100 hours across ten days. The image, the Hubble Deep Field, revealed roughly 3,000 galaxies packed into a speck of sky the size of a grain of sand held at arm's length.

— Robert Williams and the Hubble Deep Field Team, STScI, Hubble Deep Field — Released January 1996