In 1995, astronomer Bob Williams wanted to point the Hubble Space Telescope at a patch of sky filled with absolutely nothing remarkable. For 100 hours.

It was a terrible idea, his colleagues told him, and a waste of valuable telescope time. People would kill for that amount of time with the sharpest tool in the shed, they said, and besides — no way would the distant galaxies Williams hoped to see be bright enough for Hubble to detect.

Plus, another Hubble failure would be a public relations nightmare. Perceptions of the project, which had already cost multiple billions of dollars, were pretty dismal. Not much earlier, astronauts had dragged Hubble into the cargo bay of the space shuttle Endeavour and corrected a disastrous flaw in the prized telescope’s vision. After the fix, the previously blind eye in the sky could finally see stars as more than blurred points of light. And now, finally, it was time to start erasing the frustrations of Hubble’s early years.

Except that staring at nothing and coming up empty didn’t seem like the best way to do that.

But Williams was undeterred. And, to be honest, it didn’t really matter how much his colleagues protested. As director of the Space Telescope Science Institute, he had a certain amount of Hubble’s time at his personal disposal. “The telescope allocation committee would never have approved such a long, risky project,” he explains. “But as director, I had 10 percent of the telescope time, and I could do what I wanted.”

Wiliams suspected the billion light-year stare might capture eons of galactic evolution in a single frame and uncover some of the faintest, farthest galaxies ever seen. And to him, the potential observations were so important and so fundamental for understanding how the universe evolved that the experiment was a no-brainer, consequences be damned.

“Scientific discovery requires risk,” Williams says. “And I was at a point in my career where I said, “If it’s that bad, I’ll resign. I‘ll fall on my sword.’”

So, with his job perhaps on the line, Williams went off, put together a small team of post-docs, and did exactly as he’d planned. For 100 hours, between Dec. 18 and 28, Hubble stared at a patch of sky near the Big Dipper’s handle that was only about 1/30th as wide as the full moon. In total, the telescope took 342 pictures of the region, each of which was exposed for between 25 and 45 minutes. The images were processed and combined, then colored, and 17 days later, released to the public.

It turned out that “nothing” was actually stuffed with of galaxies. More than 3,000 of them came spilling out, some roughly 12 billion years old. Spiral, elliptical, irregular – red, white, blue, and yellow – the smudges of light that leapt from the final composite image cracked the universe in ways scientists never could have imagined.

View Images The Hubble Deep Field at full resolution. Click to enlarge. (R. Williams, the Hubble Deep Field team, NASA)

“With this achievement, the estimated number of galaxies in the universe had multiplied enormously — to 50 billion, five times more than previously expected,” wrote John Noble Wilford in The New York Timesin The New York Times. And some of the older galaxies – those distant, faint ones that were supposedly impossible for Hubble to see – looked really, really different.

“When the galaxies were young, they were very irregular — they were having collisions, they were erupting, they were having adolescent outbursts,” says Robert Kirshner of the Harvard-Smithsonian Center for Astrophysics. He was among the scientists who initially thought the deep field was a bad idea. “Bob was right, I was wrong. The use of that discretionary time was a courageous thing,” he says.

But there was more. Williams had gotten in touch with astronomers at the Keck telescopes in Hawaii ahead of time and asked them to point their Earth-based guns at the same patch of sky. Together, the observations helped astronomers develop something of a shortcut for determining cosmological distances to these galaxies, unlocking large portions of the universe.

As for public relations? The image now known as the Hubble Deep Field captivated pretty much everyone. To say it was a triumph would be an understatement. “The nerve that it took to say, ‘We’re going to point where there isn’t anything,’ was interesting,” says John Mather, a Nobel Laureate and senior project scientist for the James Webb Space Telescope. “And Bob Williams got a lot of nice recognition for that leadership.”

Not long after, Williams’ experiment was repeated in a different patch of sky in the southern constellation Tucana, and came to be called the Hubble Deep Field South. In 2004, a million-second exposure of nothing produced the Hubble Ultra Deep Field, filled with even more galaxies than the original. And in 2012, combining 10 years of Ultra Deep Field exposures produced the Hubble eXtreme Deep Field.

View Images Hubble eXtreme Deep Field. All these smudges, smears and spots are galaxies. (NASA/ESA/XDF/HUDF09 Team)

These images have offered “a glimpse of the hundreds of billions of galaxies that fill the universe,” says Hubble senior scientist Jennifer Wiseman, of NASA’s Goddard Space Flight Center. “That gives me and many people pause to be quiet and contemplate this majestic universe we live in, and be grateful we have a chance to look at it.”

Jason Kalirai, project scientist with the Webb telescope, goes and step further and places the Hubble Deep Field in a rather impressive historical context. “One of the questions that even the earliest civilizations probably asked themselves is, ‘What is our place in the universe?'” There have been a few times in our history when the prevailing answer to that question has been overthrown, he says. Once was when Galileo turned his telescope to Jupiter and its moons and helped show that not everything revolves around the Earth; another was when the astronomer Edwin Hubble showed, in the early 1900s, that not every speck of light in the sky belongs to our own galaxy.

A third is the Hubble Deep Field. “It showed that the universe is teeming with these galaxies, and if you do a census of how many galaxies you see, and think about how many more are in the night sky, you can conclude that there are as many galaxies as there are stars in the Milky Way,” Kalirai says.