Sharpening our cosmic focus

Three decades ago, physicist Tony Tyson sat in the control room of the U.S. National Science Foundation Víctor M. Blanco 4-meter Telescope, located on a mountaintop in Chile. At the time, the Blanco telescope, part of Cerro Tololo Inter-American Observatory, a Program of NSF NOIRLab, was one of the largest and most advanced telescopes in the world.

Tyson and his team were supporting astronomers studying galaxies and hunting for distant supernovae with a camera Tyson had helped build. What the supernova team found was unexpected: the Universe appeared to be expanding faster than any model predicted. At first, they couldn’t believe it. But as more data came in, it became undeniable.

This observation was one of the first hints that something was deeply hidden from our understanding of the Universe — a clue that would later lead to the discovery of what we call dark energy, the force behind the accelerating expansion of the Universe.

Tyson points out that “95% of the Universe is made of something we don’t understand. We have no idea what dark matter and dark energy are, which I think is really fun,” he says. “It means that there’s new physics around the corner.”

Tyson and his collaborators, who planned to use the telescope to map dark matter, were already thinking about what might come next.

“We asked ourselves: Could we build a bigger telescope to collect more light and a camera with more pixels to map the Universe?” Tyson says. “With computing power advancing rapidly to handle the enormous data such a facility would generate, it all felt possible.”

These questions inspired the effort to build the new observatory, initially called the Dark Matter Telescope project. The idea was ambitious: build a much larger telescope with a giant camera capable of scanning the entire visible sky, discovering billions of galaxies instead of just thousands. Tyson submitted an 11th-hour proposal to the 2000 National Academy of Science's Decadal Survey of Astronomy & Astrophysics, a once-in-a-decade prioritization of the field’s grandest ambitions.

“The proposal talked mostly about gravitational lensing and mirages and mapping dark matter,” he says. “But on the last page, I had a picture of an Earth-threatening asteroid. They loved that because this new telescope would do much more than just map dark matter.”

The community embraced it, renaming it first the Large Synoptic Survey Telescope (LSST). In 2019 U.S. Congress officially renamed the observatory to honor Vera C. Rubin, a pioneer in dark matter research. The LSST acronym was preserved and applied to the survey name, which now stands for the Legacy Survey of Space and Time.

Returning to the scene of the dream

Tyson, now Rubin’s chief scientist and a professor at UC Davis, has been the project’s driving force. As founding director for over a decade, he spearheaded efforts to secure private and federal funding, working with tech industry allies and academic partners, and a growing team of scientists, engineers and technicians to turn the vision into reality.

Tony Tyson and other collaborators posing with Rubin Observatory’s 8.4-meter primary mirror. The mirror, which is one component of a complex three-mirror system, took years to perfect and was crafted from a single piece of glass. The process involved collaboration with experts, and even a high school CAD drawing from the project leader’s son, Christopher. After overcoming significant design challenges the mirror was carefully crafted, transported, and installed at the observatory in Chile.

Credit: RubinObs/NOIRLab/SLAC/NSF/DOE/AURA/T. Tyson

Rubin Observatory’s defining feature is its ability to rapidly scan the entire visible southern sky with unprecedented depth and speed. Unlike traditional observatories, which focus on narrow areas, Rubin’s 8.4-meter telescope and its 3200-megapixel camera will capture 10-square-degree images — an area of sky equivalent to about 45 full Moons — roughly every 40 seconds.

“We’ll cover the sky repeatedly over 10 years,” Tyson says, “sending alerts within two minutes for anything that moves or explodes.”

This unmatched speed enables real-time detection of transient events like supernovae, asteroids, and other cosmic phenomena.

The Rubin group chose to build the observatory on Cerro Pachón, just a few kilometers from where Tyson first dreamed up the project, to benefit from the minimal cloud cover, low light pollution, and stable atmospheric conditions. The unique design of the telescope allows for extremely rapid repointing that is crucial for Rubin, as it allows the telescope to efficiently scan large portions of the sky, capture transient events, and gather data in real time.

Time to focus

At the heart of Rubin’s groundbreaking observations is the largest digital camera ever built, constructed at the Department of Energy’s SLAC National Accelerator Laboratory. Tyson said the group chose SLAC in part for its state-of-the-art facilities, skilled engineers, and proven track record, but the deciding factor was the team. With experienced leaders like Steve Kahn, who served as Director of the LSST Camera project (and later as Rubin Observatory Director) and led the initial camera work, along with the involvement of skilled engineers and talented students, the team’s expertise and commitment were crucial to the success of the LSST Camera's construction.

Credit: RubinObs/NOIRLab/SLAC/NSF/DOE/AURA/B. Quint

“You need all those things — facilities, scientists, engineers, and experience — but most importantly, you need people who are committed to taking ownership of the camera,” Tyson says. “In the end, it was obvious that SLAC was the right place to do it.”

New physics around the corner

The observatory will tackle some of the Universe’s greatest mysteries, including dark matter and dark energy.

Tyson sees these unknowns as opportunities for Rubin to uncover clues that could rewrite our understanding of physics. Using weak gravitational lensing, Rubin will map dark matter with unparalleled precision. This technique measures how massive foreground galaxies bend light from distant background galaxies, creating a ‘cosmic mirage’ that distorts their shapes — a distortion scientists will use to ‘weigh’ the unseen dark matter holding galaxies together. They will also track how fast the Universe is expanding, testing whether that speed varies over time.

Over the next decade, Rubin will catalog an estimated 17 billion stars, 20 billion galaxies, and millions of astronomical phenomena, generating 60 petabytes of raw data. Hundreds of petabytes of data will be processed in total, including simulations to test models of the Universe, all made possible by advancements in computing power. After its 10-year survey, Rubin’s flexible design could accommodate new instruments, extending its scientific lifespan.

Credit: Illustration by Sandbox Studio, Chicago with Thumy Phan for Symmetry Magazine

Rubin’s data will complement other observatories like the Euclid Space Telescope and the Nancy Grace Roman Space Telescope, enhancing measurements with additional tools to probe the Universe’s expansion history with greater precision. Beyond cosmology, its rapid scans will catalog millions of supernovae, asteroids, and other transient objects, providing a dynamic, real-time census of the sky.

Rubin’s data policy ensures that a significant portion of the data it generates will eventually be accessible to anyone, not just professional astronomers and physicists, allowing the public to explore the cosmos in unprecedented detail.

For Tyson, now that construction is almost complete, the excitement lies in the unknown. More powerful technology and cutting-edge equipment increase the chances of discovering something new and unexpected.

“I’m eager to see what others might uncover by examining the data with fresh eyes,” he says. “Someone, maybe a citizen scientist, will look at the data and see something that doesn’t fit any known category — like a new kind of cosmic object — and that could lead to a breakthrough that changes our understanding of the Universe.”