Ten days staring at an empty patch of sky

In December 1995, the team behind the Hubble telescope made a risky bet: point it for ten days at a tiny, apparently empty scrap of sky near the Big Dipper. A patch as small as a grain of sand held at arm's length. Many considered it a waste of a very expensive telescope.

The final image, built from hundreds of exposures, revealed about three thousand points of light. Almost none of them were stars. They were galaxies — each holding billions of stars, some so distant that their light had been travelling for most of the history of the universe.

That photo, the Hubble Deep Field, taught us something dizzying: there is no such thing as empty sky. Pick the blackest corner of the night, look patiently enough, and you will find thousands of galaxies waiting. Nothingness turned out to be packed.