Circles upon Circles above Gemini South Observatory in Chile | NOIRLab
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Unlike this image suggests, the sky has not suddenly become bright—it is just a photographic trick. Atop Cerro Pachón in Chile, many exposures of the dark night capture the stars’ journey across the sky, along with the setting Sun (far right), the headlights of a car passing by on the road (left), and the lasers of the adaptive optics on both Gemini South (middle) and Andes Lidar Observatory (left). Gemini South is one half of the International Gemini Observatory, operated by the National Science Foundation (NSF) NOIRLab, while the Andes Lidar Observatory is part of Cerro-Tololo Inter-American Observatory (CTIO), a Program of NSF NOIRLab. To the right, in the distance, sits NSF–Department of Energy (DOE) Vera C. Rubin Observatory, a joint initiative of the U.S. National Science Foundation (NSF) and the U.S. DOE Office of Science (DOE/SC), and operated jointly by NSF NOIRLab and DOE’s SLAC National Accelerator Laboratory.
Nights on the mountain top are pristinely dark, so capturing the right amount of light is key for astronomers and photographers alike, and they both use different techniques to do just that. The photographer and NOIRLab Audiovisual Ambassador Petr Horálek captured multiple images over the course of the night and then stacked them on top of each other, finding the perfect balance of dark and light for us to see the thousands of mesmerizing star trails.
Star trails are caused by the Earth’s rotation. It makes stars appear to move in arcs and circles around the Earth’s celestial poles (the celestial south pole is seen to the left in this image). The distance of each star to the pole star helps us define that stars are circumpolar or seasonal. Circumpolar stars do not rise or set like the Sun—they would even be continuously visible during the day at any time of the year if not for the Sun’s light. Meanwhile, seasonal stars rise in the east and set in the west, changing with the seasons due to their proximity to the celestial equator. These pathways are an effect of the geometry of Earth’s orbit, and the latitude you observe the sky from will change what stars appear circumpolar.
The Gemini South Telescope, half of the International Gemini Observatory, shines a low power laser into the sky to create a laser guide star. This laser guide star serves as a reference for the telescope's adaptive optics system so that it can 'cancel out' the effect of atmospheric turbulence on the images of its actual targets. The Gemini South telescope is located on a mountain in the Chilean Andes called Cerro Pachón, where very dry air and negligible cloud cover make this another prime telescope location.
https://noirlab.edu/public/programs/gemini-observatory/gemini-south/
Release Date: Aug. 20, 2025
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