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The Very Large Telescope Project (VLT) consists of a system of four separate optical telescopes (the Antu telescope, the Kueyen telescope, the Melipal telescope, and the Yepun telescope) organized in an array formation. Each telescope has a 8.2 meter aperture. The project is organized by the European Southern Observatory.

VLT is located at the Paranal Observatory on Cerro Paranal, a 2,635-m high mountain in the Atacama desert in northern Chile.

General information

The VLT consists of a cluster of four large telescopes, and an interferometer (VLTI) which will be used to resolve fine features. The telescopes have been named after the names of some astronomical objects in the local Mapuche language: Antu (The Sun), Kueyen (The Moon), Melipal (The Southern Cross), and Yepun (Venus)

The VLT can be operated in three modes:

• as a set of independent telescopes
• as a single large incoherent instrument, for extra light-gathering capacity (this mode has now been abandoned)
• as a single large coherent interferometric instrument, for extra resolution

In its full interferometric operating mode, the four telescopes provide the same light gathering ability (neglecting light losses from the throughput of the instrument) as a single 16m telescope, making it the largest optical telescope in the world (the interferometric technique used at the VLTI is not suitable for observing very faint sources however). The VLT is intended to achieve an effective angular resolution of 0.001 arcsecond at a wavelength of 1 µm, comparable to that achieved using other arrays such as the Navy Prototype Optical Interferometer and the CHARA Array.

The poor brightness sensitivity of interferometric observations mean that they could not be used for imaging objects with low surface brightness such as the moon (unless a powerful artificial light source was placed on the surface of the moon to act as a reference -- note that the moon only provides a lot of light on Earth because it covers such a large area of the night sky). Only targets which are at temperatures of more than 1000 Centigrade have a surface brightness high enough to be observed in the mid-infrared, and objects must be at several 1000s of degrees for near-infrared observations using the VLTI. This sensitivity limit rules out interferometric observations of most solar-system objects apart from the Sun. All the stars visible to the naked eye have temperatures of several 1000 degrees, and have large enough surface brightnesses and angular sizes to be observed by the VLTI. Although the use of large telescope diameters and adaptive optics correction can improve the sensitivity a small amount, this cannot extend the reach of optical interferometry beyond nearby stars and the brightest active galactic nucleii.

The VLT is operated by the European Southern Observatory.

Related topics

• List of observatories
• List of optical telescopes
• List of astronomical interferometers at visible and infrared wavelengths
• Overwhelmingly Large Telescope
• Giant Magellan Telescope
• Misplaced Pages Project: Telescopes

External links

• ESO VLT - official site.
• Telescope to challenge moon doubters
• Dimensions of the Lunar Module
• ASTROVIRTEL Accessing Astronomical Archives as Virtual Telescopes including archives from the VLT

• Chile
• Telescopes
• Astronomical observatories