UT4 at Paranal Observatory shoots lasers into the sky to make artificial stars, helping it correct for atmospheric blur and capture crystal-clear cosmic images. Credit: ESO/A. de Burgos Sierra
At the Paranal Observatory, the UT4 telescope doesn’t just stargaze—it actively creates its own stars using powerful lasers to battle atmospheric turbulence.
Thanks to its advanced adaptive optics system, UT4 delivers incredibly sharp images from the ground, rivaling the view from space.
A Majestic Night at Paranal
This majestic image captures a stunning view of UT4, one of the four 8-meter telescopes that make up ESO’s Very Large Telescope (VLT) at Paranal Observatory. Set against a sky filled with stars, UT4 is far more than a passive stargazer. Inside its dome, the telescope sends out four brilliant laser beams that cut through the quiet night.
Creating Stars with Lasers
The lasers come from the 4 Laser Guide Star Facility (4LGSF), a system that allows UT4 to create artificial stars high in the atmosphere. The lasers excite sodium atoms about 90 kilometers above the ground, making them glow brightly. These glowing points act as “guide stars.” By observing how these artificial stars are distorted by the Earth’s atmosphere, the telescope can determine how to correct for the same turbulence that makes natural stars twinkle.
Mastering the Twinkling Atmosphere
To make these corrections, UT4 uses its adaptive optics system. This system can precisely adjust the shape of the telescope’s secondary mirror in real-time, counteracting the blurring effects of the atmosphere. Thanks to adaptive optics, UT4 can capture images from the ground that are almost as sharp as those taken from space.
Building a Virtual Telescope Future
Soon, the other three 8-m telescopes of the VLT will be equipped with one laser each. This is part of a series of upgrades of the VLT Interferometer and its GRAVITY+ instrument, which can combine the light of several telescopes to create a huge “virtual” telescope. Another massive eye on the sky, ESO’s Extremely Large Telescope (ELT), is nearing completion not far from Paranal, and will be equipped with at least 6 lasers, to deliver the sharpest images possible with a ground-based telescope.
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