The Vera C. Rubin Observatory, formerly the Large Synoptic Survey Telescope (LSST), is an astronomical observatory in Coquimbo Region, Chile. Its main task is to conduct an astronomical survey of the southern sky every few nights, creating a ten-year time-lapse record, termed the Legacy Survey of Space and Time (also abbreviated LSST). The observatory is located on the El Peñón peak of Cerro Pachón, a mountain in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes. The base facility is located about away from the observatory by road, in La Serena.
The observatory is named for Vera Rubin, an American astronomer who pioneered discoveries about galactic rotation rates. It is a joint initiative of the U.S. National Science Foundation (NSF) and the U.S. Department of Energy's (DOE) Office of Science and is operated jointly by NSF NOIRLab and SLAC National Accelerator Laboratory.
The Rubin Observatory houses the Simonyi Survey Telescope, a wide-field reflecting telescope with an 8.4-meter primary mirror. It uses a variant of three-mirror anastigmat to deliver sharp images over a 3.5-degree-diameter field of view. Images are recorded by a 3.2-gigapixel charge-coupled device imaging (CCD) camera, the largest camera yet constructed.
Rubin saw first light in June 2025 and started full survey operations in July 2026, taking an image of the night sky every 40 seconds in order to complete a full scan of the southern sky every few days for the next ten years. The observatory is expected to catalog millions of supernovae, more than five million asteroids (including ~100,000 near-Earth objects), and image approximately 17 billion stars and 20 billion galaxies.
Name
The telescope was originally named the Large Synoptic Survey Telescope, where the word synoptic—derived from the Greek words σύν (syn 'together') and ὄψις (opsis 'view')—describes observations that give a broad view of a subject. In June 2019, the observatory was renamed the Vera C. Rubin Observatory as proposed by United States Representative Eddie Bernice Johnson and Resident Commissioner of Puerto Rico Jenniffer González-Colón. The renaming was enacted as United States law on 20 December 2019, and announced at the 2020 American Astronomical Society winter meeting. The name honors Rubin and her colleagues' probes of the nature of dark matter by mapping and cataloging billions of galaxies through space and time.
The telescope itself is named the Simonyi Survey Telescope, in recognition of private donors Charles and Lisa Simonyi.
The LSST acronym was repurposed to refer to the survey that the observatory will perform as the "Legacy Survey of Space and Time", with the camera as the "LSST Camera".
History The Rubin Observatory was proposed in 2001 as the LSST. Construction of the mirror began in 2007 with private funds. The LSST then became the top-ranked large ground-based project in the 2010 Astrophysics Decadal Survey, and officially began construction on 1 August 2014. Funding came from the NSF, DOE, and private funding raised by the private LSST Discovery Alliance. Operations are managed by the Association of Universities for Research in Astronomy (AURA). Construction cost was expected to be about $680 million.
Site construction began in April 2015. The first pixel with the engineering camera came in October 2024, while system first light images were released 23 June 2025. Full survey operations began on 30 June 2026, having been delayed by COVID-related issues.
The Rubin Observatory is the successor to a tradition of sky surveys. These started as visually-compiled catalogs in the 18th century, such as the Messier catalog. This was replaced by photographic surveys, starting with the 1885 Harvard Plate Collection, the National Geographic Society – Palomar Observatory Sky Survey, and others. By about 2000, the first digital surveys, such as the Sloan Digital Sky Survey (SDSS), began to replace the earlier photographic plate surveys.
The Rubin Observatory evolved from the Dark Matter Telescope, mentioned as early as 1996. The fifth decadal report, Astronomy and Astrophysics in the New Millennium, was released in 2001, and recommended the "Large-Aperture Synoptic Survey Telescope" as a major initiative. Even at this early stage the basic design and objectives were set:
The Large-aperture Synoptic Survey Telescope (LSST) is a 6.5-m-class optical telescope designed to survey the visible sky every week down to a much fainter level than that reached by existing surveys. It will catalog 90 percent of the near-Earth objects larger than 300 m and assess the threat they pose to life on Earth. It will find some 10,000 primitive objects in the Kuiper Belt, which contains a fossil record of the formation of the solar system. It will also contribute to the study of the structure of the universe by observing thousands of supernovae, both nearby and at large redshift, and by measuring the distribution of dark matter through gravitational lensing. All the data will be available through the National Virtual Observatory, providing access for astronomers and the public to very deep images of the changing night sky.
Early development was funded by small grants, with major contributions in January 2008 by software billionaires Charles and Lisa Simonyi and Bill Gates, of $20 million and $10 million, respectively. $7.5 million was included in the U.S. President's FY2013 NSF budget request. DOE funded the digital camera component built by the SLAC National Accelerator Laboratory, as part of its mission to understand dark energy.
NSF funding for the rest of construction was authorized on 1 August 2014. The lead organizations are:
The SLAC National Accelerator Laboratory to design and construct the LSST camera The National Optical Astronomy Observatory to provide the telescope and site team The National Center for Supercomputing Applications to construct and test the archive and data access center The Association of Universities for Research in Astronomy to oversee construction
In May 2018, the United States appropriated more funding for the telescope than had been requested, to speed construction and operation. Telescope management was unsure this would help, since at that stage of construction they were not cash-limited.
The first photons resolved by the complete instrument were detected on 15 April 2025, appearing as rings before the instrument was adjusted to focus them as dots. Images from the first light of the full telescope and camera combination were released on 23 June 2025. The first teasers were a composite image of the Trifid and Lagoon nebulae and extracts from a wide-field view of galaxies in the Virgo Cluster. The image of the Virgo Cluster was taken in early May over four nights. The early images showed over 2,000 new asteroids. Watch parties for the release were held across six continents as people from 28 countries had been involved. An early discovery was the unusually large and quickly rotating asteroid in the Main Belt.
Simonyi Survey Telescope The Simonyi Survey Telescope design is unique among large telescopes (8-meter-class primary mirrors) for its wide field of view: in diameter, or . For comparison, both the Sun and the Moon, as seen from Earth, are about in apparent diameter and each covers an apparent area of about . Combined with its large aperture (and thus light-collecting ability), this gives Rubin a large etendue of 319 m2⋅deg2. This is more than three times the etendue of other large-entendue telescopes, the Subaru Telescope with its Hyper Suprime Camera and Pan-STARRS, and more than an order of magnitude larger than most large telescopes.
Optics
The earliest reflecting telescopes used spherical mirrors that were easy to fabricate and test. However, because they suffer from spherical aberration; a long focal length was needed to achieve a tolerable level of spherical aberration. Making the primary mirror parabolic removes spherical aberration on-axis, but the field of view is then limited by off-axis coma. Such a parabolic primary, with either a prime or Cassegrain focus, was the most common optical design up through the Hale Telescope in 1949. After that, telescopes mostly used the Ritchey–Chrétien design, using two hyperbolic mirrors to remove both spherical aberration and coma, increasing the useful field of view, limited by astigmatism and higher-order aberrations. Most later large telescopes used this design—for example, the Hubble and Keck telescopes. LSST instead uses a three-mirror anastigmat to cancel astigmatism by employing three non-spherical mirrors. The result is sharp images over a wide field of view, at the expense of some light-gathering power due to the large tertiary mirror obscuring part of the optical path.
The telescope's primary mirror (M1) is in diameter, the secondary mirror (M2) is in diameter, and the tertiary mirror (M3), inside the ring-like primary, is in diameter. The secondary mirror is the largest convex mirror in any operating telescope. (It will be surpassed by the Extremely Large Telescope's 4.2-meter secondary when complete). The second and third mirrors reduce the primary mirror's light-collecting area to , with an effective aperture equivalent to a diameter single mirror. Multiplying the collecting area by the field of view produces an étendue of 336 m2⋅deg2; the actual figure is reduced by vignetting.
The primary and tertiary mirrors (M1 and M3) are formed from a single piece of glass, the M1M3 monolith. Placing the two mirrors in the same location minimizes the overall length of the telescope, making it easier to quickly reorient. Making them from the same piece of glass results in a stiffer structure than two separate mirrors, contributing to rapid settling after motion.
The optics includes three corrector lenses to reduce aberrations. These lenses, and the telescope's filters, are built into the camera assembly. The first lens, at 1.55 m in diameter, is the largest non-compound lens ever built, and the third lens forms the vacuum window in front of the focal plane.
Unlike many telescopes, Rubin does not attempt to compensate for atmospheric dispersion. Such correction, which requires adjusting an additional element in the optical train, would be difficult to achieve in the 5 seconds available between pointings. It is also a technical challenge due to the short focal length. As a result, shorter wavelength bands away from the zenith have reduced image quality.
Wavefront sensing The telescope uses an active optics system, with wavefront sensors at the corners of the camera, to keep the mirrors accurately figured and in focus. The field of view is too large to use adaptive optics to correct for atmospheric seeing. Sensing occurs in three stages:
Laser trackers make sure the components are centered and are close to the intended positions. Open-loop corrections are applied to correct for intrinsic mirror aberrations, component sag as a function of elevation and temperature, and filter selection. Focus and figure measurements are made by sensors at the corners of the field of view to correct the optics.
The precise shape and focus of the mirror assembly is estimated, and then corrected, by comparing the images on four sets of deliberately defocused CCDs (one in front of the focal plane and one behind, see figure). One correction method proceeds analytically, estimating a Zernike polynomial description of the current shape of the mirror, and from this computing a set of corrections to restore figure and focus. Another method, considerably faster, uses machine learning for this task.
Camera