Lasers Passing through Thin Earth Clouds | ESO's Very Large Telescope in Chile

Lasers Passing through Thin Earth Clouds | ESO's Very Large Telescope in Chile

Four laser beams shine across the magnificent Southern sky in this timelapse video. Each laser comes from one of the four Unit Telescopes (UTs) of the European Southern Observatory’s Very Large Telescope (VLT), here working together as part of the VLT Interferometer (VLTI). A glowing bead of light appears sequentially on each beam, produced by the interaction of each laser with passing thin clouds. These spots were a happy accident, as the lasers themselves target a much higher layer in our atmosphere: 90 kilometers above the Earth’s surface.

Notice the bright band of the Milky Way galaxy present, along with the Lagoon and Trifid nebulae (both around 5000 light years away) to the left.

Laser guide star systems shoot artificial points of light high up into Earth's atmosphere, giving telescopes a solid reference for fixing image distortion from air turbulence. By providing a controllable and reliable calibration source, they let adaptive optics systems create sharper, more accurate astronomical images from Earth-based observatories. This technology lets big ground-based telescopes rival the clarity of space-based instruments, but without the huge cost and challenges of operating telescopes in orbit.

Four laser beams shine across the magnificent Southern sky in this picture. Glowing beads of light, one on each beam, are created by a thin layer of clouds crossing the path of the lasers and hint at the source of these beams. Emitted by the four Unit Telescopes (UTs) of the European Southern Observatory’s Very Large Telescope (VLT), here working together as part of the VLT Interferometer (VLTI), the shape of the four bright spots mirrors the layout of the UTs. However, these spots were a happy accident caused by clouds that happened to be in the way—the lasers themselves target a much higher layer in our atmosphere.

As of November 2025, all four UTs are equipped with lasers, as part of a series of significant upgrades to the VLTI named GRAVITY+. Each laser creates an artificial “star”, 90 kilometers above the Earth’s surface, used to detect how the moving atmosphere distorts incoming light. This enables a telescope to make real-time corrections that cancel out the atmosphere’s blurring effect. “Unblurred” light from the four UTs can then be combined to make detailed observations of distant cosmic objects. This upgrade has unlocked the entire Southern sky to the VLTI by allowing the system to observe much fainter objects than before.

Credit: A. Berdeu/ESO

Duration: 11 seconds
Release Date: May 25, 2026

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