A telescope survey more than a decade in the making has produced what its builders call the largest two-dimensional picture of the sky ever assembled. The release catalogs billions of galaxies, stars and quasars across most of the visible sky, stitched together from years of nightly observations into a single continuous mosaic. It is not, on its own, a map of the universe in three dimensions, but it is the foundation that a separate, even larger 3D effort is built on top of. The team behind it says the new release is both a scientific dataset and a public resource that other astronomers can mine for years.
A Deep Photograph Covering Most of the Sky
The DESI Legacy Imaging Surveys team describes its eleventh data release, known as DR11, as the largest two-dimensional map of the universe ever produced. The release is essentially a deep photograph of the sky: it records where galaxies and stars appear and how bright they are, without yet measuring how far away each one sits.
According to the release covered by Phys.org, DR11 spans roughly 75% of the sky and is built from 5.6 trillion pixels of imaging data, cataloging nearly four billion individual objects. The imaging behind it was collected over 13 years, making the final release the product of more than a decade of nightly telescope time rather than a single observing run.
The Telescope Behind the Mosaic
The imaging was captured using the Nicholas U. Mayall 4-meter Telescope, operated by NOIRLab at Kitt Peak National Observatory in Arizona. The Mayall has spent years scanning the sky in visible and near-infrared light, building up the layered exposures that were later combined into the finished survey.
NOIRLab’s own release describes the new imaging surveys map as the foundation for an even larger three-dimensional map of the universe, one built by combining the 2D positions and brightness measurements in DR11 with distance data gathered separately. The observatory’s writeup of the release is available on its public news page.
Kitt Peak’s high, dry desert location was chosen decades ago precisely because it offers the kind of steady, dark night skies that a survey of this length depends on. Repeating the same patches of sky over years of observing nights, rather than photographing each region once, is part of what let the Mayall build up the depth and consistency needed for a catalog this large.
Cataloging Billions of Galaxies and Quasars
The practical value of a survey this size comes from its scale. With optical images of tens of millions of galaxies and quasars embedded in a catalog of nearly four billion objects total, DR11 gives astronomers a dataset large enough to study rare types of galaxies, distant quasars, and transient events that would be missed in a smaller survey simply because too few examples would show up.
That scale also makes the release useful well outside its original purpose. Researchers studying galaxy evolution, dark matter, and even asteroids passing through the surveyed patches of sky can search the same dataset for their own targets, since the imaging was collected broadly rather than aimed at any single class of object. A survey built for one instrument’s target list often ends up cited by studies that have nothing to do with the mission that funded it, simply because so much of the sky is covered at consistent depth and quality.
Feeding a Three-Dimensional Map of Dark Energy
DESI, the Dark Energy Spectroscopic Instrument, was commissioned in 2012 with the goal of measuring the effect of dark energy on the expansion of the universe. To do that, the instrument needs to know not just where objects appear in the sky but how far away each one is, which requires spreading their light into a spectrum and measuring how much it has shifted.
The 2D imaging in DR11 is the first step in that process. It gives DESI’s target-selection software a catalog of galaxies and quasars to choose from before the spectroscopic instrument measures their distances one by one, ultimately assembling those measurements into the three-dimensional map of the universe that is DESI’s primary scientific goal.
That two-step design, a wide photographic survey followed by targeted spectroscopy, is common in modern cosmology because measuring a precise distance to every single object in the sky would take far longer than photographing them. Selecting the most useful targets from a deep image first, then spending spectroscopic time only on those, is what makes a project the size of DESI feasible within a normal observing schedule.
Processing 5.6 Trillion Pixels Faster
Turning that much raw imaging into a finished catalog required new computing infrastructure as much as new telescope time. The DESI team built a GPU-accelerated version of its processing pipeline specifically for DR11, a change that sped up some of the most computationally demanding stages of turning raw pixel data into a calibrated, searchable catalog.
Work of that scale was carried out with help from the National Energy Research Scientific Computing Center, whose own account of the release describes the computing effort behind the map in detail. The dataset is now available for other researchers to search and download, extending its use well past the DESI collaboration that built it.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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