What strikes the eye in this seemingly ordinary image of an astronomical observatory are the laser beams piercing the darkness. This image is not just aesthetic; it illustrates an advanced method for observing the cosmos with unprecedented accuracy.
This photograph, captured by astrophotographer Alexis Trigo at the Paranal Observatory, home to the telescopes that collectively form the "Very Large Telescope (VLT)", shows the four telescopes named Antu, Kueyen, Yepun, and Melipal. Each has a primary mirror measuring 8.2 meters (about 27 feet) in diameter, allowing for the study of distant exoplanets or remote galaxies. A small auxiliary telescope is visible in the foreground, mobile on rails to increase light-gathering capacity when needed.
The Milky Way shines above the Very Large Telescope in Chile. Credit: A. Trigo/ESO The lasers visible in the image are aimed at Earth's upper atmosphere. At an altitude of about 90 kilometers (56 miles), they hit sodium atoms, which then glow like small bright points. These beacons serve as targets for adaptive optics systems, which correct the blurring effects caused by the atmosphere in real-time.
This adaptive optics is a cornerstone of modern telescopes. By tracking the fluctuating movement of these artificial guide stars, it's possible to deduce the optical perturbations caused by the atmosphere in real-time. The deformable mirrors of the observatories then adjust their shape several times per second. This action compensates for atmospheric turbulence, theoretically providing images as sharp as if the instrument were in space. This improvement is crucial for detecting planets around other stars or observing minuscule details in galaxies.
Until recently, only the Melipal telescope was equipped with these lasers. In December 2025, the three other large telescopes received their own systems, forming a constellation of guide stars. The Very Large Telescope can now operate with increased precision, particularly for interferometric instruments like the VLTI and GRAVITY+, which combine light from multiple telescopes.
Thanks to these advances, astronomers are gathering more detailed information about the cosmos. The ability to correct atmospheric distortions opens new opportunities for discoveries about star formation, the nature of black holes, or the search for signs of life on exoplanets. The Paranal Observatory thus remains at the forefront of celestial exploration.