The Very Large Telescope (VLT), run by the European Southern Observatory, is pictured beneath a sweeping Milky Way above Chile’s Atacama Desert. Airglow — a faint green and red glow from chemical reactions in the upper atmosphere — tints the horizon and is visible only in exceptionally dark places. Astronomers warn that light pollution, expanding cities, growing satellite constellations and industrial development threaten these rare dark sites, posing scientific, environmental and cultural risks.
Milky Way Arcs Over ESO’s Very Large Telescope — Airglow Paints the Atacama Night
The Very Large Telescope (VLT), run by the European Southern Observatory, is pictured beneath a sweeping Milky Way above Chile’s Atacama Desert. Airglow — a faint green and red glow from chemical reactions in the upper atmosphere — tints the horizon and is visible only in exceptionally dark places. Astronomers warn that light pollution, expanding cities, growing satellite constellations and industrial development threaten these rare dark sites, posing scientific, environmental and cultural risks.
04:02, 06.11.2025Science
Milky Way and Airglow Frame the Very Large Telescope
High on the dry plateaus of Chile’s Atacama Desert, one of humanity’s most powerful observatories scans the heavens: the Very Large Telescope (VLT), operated by the European Southern Observatory (ESO). In a recent image, three of the VLT’s domes sit beneath a sweeping band of the Milky Way while a faint green-and-red glow — known as airglow — tinges the horizon.
Airglow is a natural optical emission produced by chemical reactions in Earth’s upper atmosphere. When atoms and molecules that were excited by sunlight or other processes relax, they emit photons. Different atoms and molecules produce different colors, so airglow can appear subtly green, red or orange depending on the chemistry involved.
The VLT is perched in the high Andes within the Atacama Desert — one of the planet’s clearest, darkest places for astronomy. Airglow is extremely faint and is usually hidden by artificial light; only in exceptionally dark locations can this gentle atmospheric glow be seen with the naked eye.
Why Dark Skies Matter
Those pristine dark conditions are precisely what make the VLT’s site so valuable. Astronomers are increasingly concerned that even remote observatories may lose their advantage as the night sky brightens. Urban expansion, growing networks of satellites, and industrial development all contribute to the erosion of natural darkness, reducing the sensitivity of ground-based telescopes and diminishing cultural and environmental values tied to starry skies.
Protecting dark-sky sites is both a scientific priority — to preserve the ability to observe faint celestial objects — and a cultural and environmental one, preserving humanity’s view of the cosmos.
To learn more, explore resources about the Very Large Telescope and the role of ground-based observatories in modern astronomy.