The Very Large Telescope (VLT) is an astronomical facility operated since 1998 by the European Southern Observatory, located on Cerro Paranal in the Atacama Desert of northern Chile.

These optical telescopes, named Antu, Kueyen, Melipal, and Yepun (all words for astronomical objects in the Mapuche language), are generally used separately but can be combined to achieve a very high angular resolution.

[1] The VLT's 8.2-meter telescopes were originally designed to operate in three modes:[5] The UTs are equipped with a large set of instruments permitting observations to be performed from the near-ultraviolet to the mid-infrared (i.e. a large fraction of the light wavelengths accessible from the surface of the Earth), with the full range of techniques including high-resolution spectroscopy, multi-object spectroscopy, imaging, and high-resolution imaging.

In particular, the VLT has several adaptive optics systems, which correct for the effects of atmospheric turbulence, providing images almost as sharp as if the telescope were in space.

This design minimises any adverse effects on the observing conditions, for instance from air turbulence in the telescope tube, which might otherwise occur due to variations in the temperature and wind flow.

The interferometry (combining light from multiple telescopes) is used about 20 percent of the time for very high-resolution on bright objects, for example, on Betelgeuse.

[1] It had long been ESO's intention to provide "real" names to the four VLT Unit Telescopes, to replace the original technical designations of UT1 to UT4.

In March 1999, at the time of the Paranal inauguration, four meaningful names of objects in the sky in the Mapuche language were chosen.

An essay contest was arranged in this connection among schoolchildren of the Chilean II Region of which Antofagasta is the capital to write about the implications of these names.

[11] Unit Telescopes 1–4 are since known as Antu (Sun), Kueyen (Moon), Melipal (Southern Cross), and Yepun (Evening Star), respectively.

The enclosure is supported by the boxy transporter section, which also contains electronics cabinets, liquid cooling systems, air-conditioning units, power supplies, and more.

During astronomical observations the enclosure and transporter are mechanically isolated from the telescope, to ensure that no vibrations compromise the data collected.

[21] The Galactic Centre team at the Max Planck Institute for Extraterrestrial Physics (MPE) used these observations to reveal these effects for the first time.

[22] Other discoveries with VLT's signature include the detection of carbon monoxide molecules in a galaxy located almost 11 billion light-years away for the first time, a feat that had remained elusive for 25 years.

The VLT and APEX teamed up to reveal material being stretched out as it orbits in the intense gravity close to the central black hole.

A flat tertiary mirror diverts the light to one of two instruments at the f/15 Nasmyth foci on either side, with a system focal length of 120 metres,[28] or the tertiary tilts aside to allow light through the primary mirror central hole to a third instrument at the Cassegrain focus.

The maximum field-of-view (at Nasmyth foci) is around 27 arcminutes in diameter, slightly smaller than the full moon, though most instruments view a narrower field.

[35]In its interferometric operating mode, the light from the telescopes is reflected off mirrors and directed through tunnels to a central beam combining laboratory.

In the year 2001, during commissioning, the VLTI successfully measured the angular diameters of four red dwarfs including Proxima Centauri.

At more challenging mid-infrared wavelengths, the VLTI can reach magnitude 4.5, significantly fainter than the Infrared Spatial Interferometer.

[63] This refers to reflection off 32 surfaces including the Coudé train, the star separator, the main delay line, beam compressor and feeding optics.

[65][66][67] After falling drastically behind schedule and failing to meet some specifications, in December 2004 the VLT Interferometer became the target of a second ESO "recovery plan".

[70] In March 2019, ESO astronomers, employing the GRAVITY instrument on their Very Large Telescope Interferometer (VLTI), announced the first direct detection of an exoplanet, HR 8799 e, using optical interferometry.

The job required battling strong winds, fixing a broken pump in a giant washing machine and resolving a rigging issue.