Free Astronomy Magazine May-June 2023

MAY-JUNE 2023 The DESI Legacy Imaging Survey expands on the data included in two earlier companion surveys: the Dark Energy Camera (DECam) Legacy Survey and the Beijing-Arizona Sky Survey. Jointly these three surveys imaged 14,000 square degrees of the sky visible from the northern hemisphere using tel- escopes at NSF’s NOIRLab’s Kitt Peak National Ob- servatory (KPNO) and Cerro Tololo Inter-American Observatory (CTIO) in Chile. This ambitious six-year effort involved three telescopes, one petabyte (1000 trillion bytes) of data, and 100 million CPU hours on one of the world’s most powerful com- puters at the US Department of Energy’s National Energy Research Scientific Computing Center. T he Universe is teeming with galaxies, each brimming with billions of stars. Though all galaxies shine brightly, many are cloaked in dust while others are so distant that to observers on Earth they appear as little more than faint smudges. By creating comprehensive maps of even the dimmest and most-distant galaxies, as- tronomers are better able to study the structure of the Universe and unravel the mysterious proper- ties of dark matter and dark energy. The largest such map to date has just grown even larger, with the tenth data release from the DOE’s Lawrence Berkeley National Laboratory’s Dark Energy Spec- troscopic Instrument (DESI) Legacy Imaging Survey. The largest two-dimensional map of the sky by NOIRLab − Charles Blue A n image centered on a relatively nearby galaxy cluster dubbed Abell 3158; light from these galaxies had a red- shift value of 0.059, meaning that it trav- eled approximately 825 million years on its journey to Earth. The image is a small part of the DESI Legacy Imaging Sur- veys — a monumental six-year survey cover- ing nearly half the sky. Most of the data for the image origi- nally were taken as part of the LoVoCCS survey. [LoVoCCS/ DESI Legacy Imaging Survey/KPNO/NOIR- Lab/NSF/AURA; Image processing: T.A. Rec- tor (University of Alaska Anchorage/ NSF’s NOIRLab, Jen Miller, M. Zamani & D. de Martin (NSF’s NOIRLab)]