Pointing at Nothing

How one astronomer bet his career on a crazy idea — pointing the most expensive telescope ever built at an empty patch of sky for 100 hours — and found a universe fuller than anyone had imagined.

The Bet

In 1995, Robert Williams, director of the Space Telescope Science Institute, made a decision that his colleagues considered reckless. He would use his discretionary time — 10% of Hubble's schedule, at his personal disposal — to point the telescope at a patch of sky near the Big Dipper that contained nothing: no known stars, no known galaxies, no known anything. For 100 hours, over ten consecutive days in December, Hubble stared at a region about 1/30th the width of the full Moon. It took 342 separate exposures.

John Bahcall, one of Hubble's founding scientists, visited Williams twice to talk him out of it. He argued the telescope would not reveal any new population of galaxies — it was a waste of precious observing time. The telescope had only recently recovered from the humiliation of a flawed primary mirror requiring an emergency spacewalk repair. Another failure could be fatal. Williams told Bahcall: “I'm willing to fall on my sword.”

When the images were combined and processed, the Hubble Deep Field showed not emptiness but abundance: over 3,000 galaxies, some dating back to within a billion years of the Big Bang. The estimated number of galaxies in the observable universe jumped from 10 billion to 50 billion. Young galaxies looked strange — irregular, colliding, bursting with star formation — nothing like the serene spirals of the modern universe. Robert Kirshner, who had opposed the idea, later admitted: “Bob was right, I was wrong. The use of that discretionary time was a courageous thing.” Williams himself understated it beautifully: “It turned out to be a neat image. Really.”

From Glass Plates to Gigapixels

For most of its history, astrophotography used photographic plates — glass coated with light-sensitive emulsion. They had a quantum efficiency of about 1%: 99% of arriving photons were wasted. They responded non-linearly to light, making brightness measurements unreliable. Yet for over a century, every astronomical discovery image — from Hubble's Cepheid variables to the expansion of the universe — was recorded on glass.

The CCD revolution of the 1980s changed everything. A charge-coupled device is a silicon chip divided into millions of light-sensitive pixels. Each photon striking the silicon liberates an electron via the photoelectric effect; those electrons accumulate in potential wells during the exposure. When read out, the charge is converted to a digital number. Modern CCDs achieve quantum efficiencies above 95%, respond linearly across a vast range, and output directly to a computer. A modern astrophotograph is not a single image but a composite: dozens or hundreds of calibrated, aligned, and stacked exposures that together reveal objects far fainter than any single frame could show.

The calibration pipeline is meticulous. Bias frames (zero-length exposures) measure each pixel's electronic offset. Dark frames (identical exposures with the shutter closed) subtract thermal noise — which is why astronomical CCDs are cooled to −120°C. Flat fields (images of a uniformly illuminated surface) correct for pixel-to-pixel sensitivity variations, vignetting, and dust motes on the optics. Only after all three corrections are applied can frames be aligned and stacked — and only after stacking does the faint structure of a galaxy, invisible in any single exposure, emerge from the noise.

The Deepest Images Ever Made

The Hubble Deep Field was only the beginning. In 2004, the Hubble Ultra Deep Field pushed deeper — 11.3 days of exposure over 400 orbits, revealing galaxies from when the universe was only 400 million years old. The Extreme Deep Field (2012) combined 10 years of Hubble observations into a single image reaching back 13.2 billion years, to within 500 million years of the Big Bang. Each generation of these images has rewritten what we know about the early universe — when the first stars ignited, how the first galaxies assembled, how quickly cosmic structure emerged from primordial gas.

Astrophotography is unique among the Earth methods because it straddles art and science. The aesthetic decisions — color balance, contrast stretch, framing — are also scientific ones: which wavelengths to emphasize, which structures to reveal, which artifacts to suppress. Every astro-image is an argument about what matters in the data. The Hubble Deep Field was an argument that looking at nothing — really looking, for a long time, with our best instruments — is sometimes the most important thing we can do. The argument won.

What the Photons Tell Us

Without astrophotography, astronomy is drawing by hand — subjective, imprecise, limited to what the eye can see in a single moment. Galileo sketched the Moon through his telescope; his drawings are beautiful but they are interpretations, not data. The first daguerreotype of the Moon, taken by John William Draper in 1840, was the beginning of objective astronomical record-keeping. From that moment forward, the history of astrophotography is the history of seeing deeper, fainter, and further back in time than the human eye — or any single observation — could ever manage.

Astrophotography taught us that the universe is not just bigger than we thought — it is richer, stranger, and more dynamic. The Hubble Deep Field multiplied the known galaxy count fivefold in a single image. The Ultra Deep Field pushed the observable horizon to within a cosmic heartbeat of the beginning. Every improvement in detector technology, every refinement of the calibration pipeline, every additional hour of integration time reveals more of what was always there, waiting for someone to point a camera at it and be patient enough to see.

Further Reading

• The Hubble Deep Field: The Most Important Image Ever Taken — Robert Williams, in the STScI Newsletter. Williams' own account of the decision and the discovery.
• The Deepest Image of the Universe Ever Taken — NASA Hubble Site. An accessible overview of the Hubble Ultra Deep Field and Extreme Deep Field, with downloadable images.
• Making Every Photon Count — Steve Richards. A comprehensive guide to modern amateur astrophotography, covering equipment, calibration, and processing techniques in detail.
• The Digital Universe: Astrophotography in the CCD Era — Harvard-Smithsonian Center for Astrophysics. The technical evolution from photographic plates to modern digital sensors.