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🏔️Space6 min read

The Rubin Observatory

A telescope in the Chilean desert is about to take a photo of the entire sky every three nights for ten years. It will discover more objects in its first year than astronomers found in the previous century.

In plain English

Imagine you wanted a photograph of every person on Earth. Every face, every house, every street corner. You would need to send photographers to every country, every city, every village, and even then, you would miss things. People move. Buildings change. New ones are built.

Now imagine you wanted to photograph the entire sky, down to objects so faint that current telescopes cannot even see them, every three nights, for ten years. And then compare those photographs so precisely that you can detect anything that changed between them: a star that flickered, an asteroid that shifted, a galaxy whose light took 8 billion years to reach us and arrived tonight.

That is what the Vera C. Rubin Observatory is doing from the top of Cerro Pachón in Chile.

It has a camera unlike anything ever built: 3,200 megapixels. A single photograph would take 1,500 high-definition TV screens to display. Every night it observes, it generates roughly 15 terabytes of data. Over the ten years of the Legacy Survey of Space and Time, the LSST, it will produce 60 petabytes of astronomical data, the largest dataset in the history of science.

The questions it is designed to answer include some of the biggest in astrophysics: What is dark matter? What is dark energy? How did the solar system form? Is there a ninth planet hiding in the outer solar system?

Five things to file under "wait, what?"

  • It will discover more asteroids in the first year than in all of human history combined. Currently, fewer than half of the near-Earth asteroids large enough to cause regional devastation have been identified. The LSST is expected to find most of them within the first few years of operation.

  • The camera alone took twenty years to design and build. The LSST Camera, now called the Rubin Observatory LSSTCam, is the largest digital camera ever constructed for astronomy. Its focal plane is the size of a large pizza. Inserting a single sensor required a clean room and micrometre-level precision.

  • It will release all its data to the public. Unlike many major observatories, the Rubin Observatory's data will be freely accessible to any astronomer in the world and, eventually, to the public. The expectation is that citizen scientists will make real discoveries in the data stream.

  • It is designed to detect things that change. Most telescope surveys look for objects at a single moment. The LSST is built around the idea of watching, returning to the same patch of sky every few nights so that anything that moves, brightens, dims, or explodes becomes visible by comparison. This is called a time-domain survey.

  • It is named for Vera Rubin, who discovered dark matter but never won a Nobel Prize. The decision to name the observatory after Rubin was made in 2019. It is one of the few major scientific facilities named for a woman in astronomy. The dark matter she found is one of the primary targets of the survey.

The full story

Why Chile?

The Andes are among the best sites on Earth for optical astronomy. The air above Cerro Pachón, at 2,650 metres elevation, is unusually dry, unusually stable, and unusually transparent. On most nights, stars barely twinkle when viewed from there. Light from the Milky Way casts shadows on the ground. The site already hosts two major international observatories; Rubin is the newest addition.

Chile's Atacama region, a few hundred kilometres to the north, hosts even more. The European Southern Observatory's Very Large Telescope Array, the ALMA radio telescope network, and the future Extremely Large Telescope are all nearby. The region has become the world's most concentrated centre of advanced astronomy.

What the LSST will look for

The survey has four main science drivers, each addressing a different open question.

Dark energy: The universe is not just expanding, it is expanding faster over time. The cause is unknown and called dark energy. By mapping the positions and redshifts of billions of galaxies, the LSST will track how the universe's expansion rate has changed over cosmic time, constraining dark energy models with unprecedented precision.

Dark matter: Gravity bends light. When light from a distant galaxy passes a large mass, it is deflected, an effect called gravitational lensing. By measuring the tiny distortions in the shapes of billions of background galaxies, the LSST will map the distribution of dark matter throughout the universe without ever detecting dark matter directly. This technique is called weak gravitational lensing, and the Rubin Observatory will be its most powerful instrument ever.

The solar system: The LSST will discover hundreds of thousands of new solar system objects: asteroids, comets, and trans-Neptunian objects in the far outer solar system. Among the things astronomers are looking for is evidence for a hypothetical ninth planet, a massive body thought to be lurking perhaps 600 astronomical units from the Sun, inferred from the unusual clustering of distant Kuiper Belt objects.

Transients: Stars that explode (supernovae), neutron stars that merge (kilonovae), black holes that swallow material (active galactic nuclei). The LSST will detect and alert astronomers to events happening across the sky in near-real-time, allowing follow-up observations by other telescopes within hours of detection.

When does it start?

First light, the first official observation, occurred in 2024. The full ten-year LSST survey began ramping up in 2025 and is expected to run through the mid-2030s.

The data pipeline is as impressive as the telescope itself. Every night's observations are processed automatically: source detection, comparison to previous images, cataloguing, and alert generation. Within 60 seconds of a change being detected, the system can send an automated alert to the global astronomical community. There will be around 10 million such alerts per night.

Why it matters beyond astronomy

The near-Earth asteroid discovery programme is perhaps the most direct public safety application. Identifying potentially hazardous objects decades before any possible impact is the only realistic way to prevent a civilisation-threatening collision. The 2013 Chelyabinsk meteor, which injured 1,500 people in Russia, was not detected in advance. Objects of that size are still largely uncatalogued.

The LSST will also generate a detailed catalogue of near-Earth asteroids large enough to cause regional devastation, completing the census that NASA began in the 1990s. If anything is found on an impact trajectory, the lead time to deflect it will be decades rather than years.

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