Surveying the Universe with Rubin Observatory

photograph of a mountain ridge with two telescopes

Rubin Observatory will sit atop the Cerro Pachón ridge in northern Chile, joining Gemini south and the Southern Astrophysical Research Telescope. [LSST Project Office]

First light for the Vera C. Rubin Observatory atop Cerro Pachón in Chile is fast approaching — the eagerly awaited facility is slated to begin observations in 2024. The observatory’s 8.36-meter Simonyi Survey Telescope will carry out the Legacy Survey of Space and Time (LSST), a 10-year endeavor that will map the entire sky visible from its location every three days.

Rubin Observatory and LSST are poised to revolutionize astronomy in ways both anticipated and unexpected; through repeated observations, LSST will enable us to detect and monitor transient events like supernovae and gamma-ray bursts, map the Milky Way, probe the nature of dark energy and dark matter, and expand our catalogs of solar system objects by more than an order of magnitude. A new focus issue of the Astrophysical Journal Supplement Series explains how astronomers used science to guide the development of the upcoming survey.

map of the LSST footprint

LSST footprint showing the number of visits as a function of position on the sky. The acronyms refer to the surveys that fall under the LSST umbrella. Click to enlarge. [Bianco et al. 2022]

The survey — which is actually a combination of multiple surveys with specific goals — is notable not only for its breadth and depth, but also its design, which incorporated input from the astronomy community at every step. The articles in the new focus issue, six of which are already published, detail the scientific rationale behind the path the survey will take across the night sky, known as the observing cadence, and explore the potential science gains to will achieve. A few of the topics explored in this focus issue include:

  • Standard candles: RR Lyrae-type variable stars show correlations between the period of their variation, their luminosities, and their colors. These relationships allow RR Lyrae stars to be used as standard candles for determining the distances to other galaxies, so precisely determining the period of their variation is critical. LSST potentially occupies the sweet spot for studying RR Lyrae stars: wide enough coverage to allow for population-wide studies of these important stars, but with short enough cadence to capture subtle changes in the period and amplitude of their variations, the cause of which is still unknown.
  • illustration of a blazar

    Artist’s impression of the jet from an active galactic nucleus directed toward Earth. [NASA/Goddard Space Flight Center Conceptual Image Lab]

    Blazar variability: Blazars — relativistic jets pointed toward Earth that emanate from distant supermassive black holes that are actively accreting material — can vary in brightness on timescales from minutes to years. LSST is expected to observe thousands of known blazars while potentially discovering thousands more, enhancing our understanding of blazar variability as well as the environments they live in.
  • The unknown: Possibly even more enticing than the science advances we expect are those that we can’t even begin to imagine. How can a survey be optimized to discover something that we know nothing about? This issue is tackled by estimating how complete the survey will be in terms of the volume of space explored, the wavelengths covered, and other factors. They key to discovery might be switching things up; survey strategies that vary exposure time and time between observations find more novel sources than those that don’t.

Rubin Observatory is notable not only for the science data it will collect during the planned 10-year duration of LSST — roughly 300 petabytes’ worth (that’s 300,000,000,000,000,000 bytes) — but also what it plans to do with it. Each night, the observatory will release data related to millions of transient and variable objects to enable immediate follow-up of intriguing targets. The 20 terabytes of data collected nightly will be processed, stored, and shared with all scientists in the United States and Chile, as well as anyone affiliated with a number of participating institutions. Two years after its collection, the data will be made available to all. A decade of exceptional data, shared widely with the community and the world? It doesn’t get much better than that!


Articles in the Rubin LSST Survey Strategy Optimization Focus Issue will be collected here.

“Optimization of the Observing Cadence for the Rubin Observatory Legacy Survey of Space and Time: A Pioneering Process of Community-focused Experimental Design,” Federica B. Bianco et al 2022 ApJS 258 1. doi:10.3847/1538-4365/ac3e72