Very Large Telescope (VLT)

The Very Large Telescope (VLT) consists of four identical 8.2-meter telescopes, known as Antu ("Sun" in the language of Chile's indigenous Mapuche people), Kueyen (Moon), Melipal (Southern Cross), and Yepen (Venus), at the European Southern Observatory's Paranal Observatory on Cerro Paranal (altitude 2,600 meters), Chile, that can work independently or together as the world's most powerful optical interferometer.


Very Large Telescope


The Very Large Telescope Interferometer (VLTI), equivalent to a single instrument with a mirror 16 meters in diameter, combines the light from the four big Unit Telescopes and from several moveable 1.8-meter Auxiliary Telescopes, spaced across baselines of up to 200 meters, by way of the Interferometric Tunnel. Inside this 130-meter-long underground cavern, the light beams gathered by the telescopes are passed through delay lines to compensate for the slightly different path-lengths they have taken in reaching the instruments. The delay lines help to synchronize the beams, before redirecting them to a central laboratory. The interference fringes produced when the beams are finally recombined provide the information needed to reconstruct the original image in unprecedented detail, giving a picture as sharp as if it had come from a single telescope 200 meters across. This gives the VLT a maximum angular resolution of about 0.001 arc-second at 1 micron wavelength (in the near-infrared), which is equivalent to about 2 meters at the distance of the Moon. (The Moon has an angular diameter of 0.5° and a linear diameter of 3476 kilometers; 0.5°/0.001" = 1,800,000; 3476 kilometers/1,800,000 ~ 2 meters). Used in interferometric as distint from individual-instrument mode, however, the VLT is only sensitive to objects with a high surface brightness, such as stars and the nuclei of active galaxies. This makes it unsuitable for observing most objects in the Solar System apart from the Sun.


In 2005, scientists using the VLT announced they had obtained the first direct photograph of an extrasolar planet – 2M1207b, which orbits the star 2M1207 more than 200 light-years away in the constellation Hydra.