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The VLT can be operated in three modes: The VLT can be operated in three modes:
* as a set of independent telescopes * as a set of independent telescopes
* as a single large incoherent instrument, for extra light-gathering capacity * 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 * 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 as a single 16m telescope, making it the largest optical telescope in the world. The VLT is intended to achieve an effective ] of 0.001 ] at a ] of 1 µm. This is an angle of 0.000000005 ]s, equivalent to resolving a target 2 meters across at the distance between the ] and ]. 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 ] technique used at the VLTI is not suitable for observing very faint sources however). The VLT is intended to achieve an effective ] of 0.001 ] at a ] of 1 µm, comparable to that achieved using other arrays such as the ] and the ].


The poor brightness sensitivity of ] observations mean that they could not be used for imaging objects such as the moon (unless a powerful artificial light source was placed on the surface of the moon to act as a reference). Only targets which are at temperatures of more than 1000 Centigrade are bright 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 ] 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 angular sizes to be observed by the VLTI.
This should easily resolve the 5-metre wide Lunar Module bases left on the Moon by the ] moon missions, and a group of European scientists intends to do just that to challenge ].

The VLT is operated by the ].


==Related topics== ==Related topics==

Revision as of 14:38, 17 February 2005

The four telescopes of the European Southern Observatory Paranal site. The VLTI (Very Large Telescope Interferometer) building is the low structure in front of the telescopes. Image courtesy of the European Southern Observatory.
File:Vlt.kueyen.arp.750pix.jpg
One of the four telescopes that make up the VLT, named Kueyen. The 8.2 meter mirror can be seen below the large horizontal grey beam (as an oval patch of lightness). Image courtesy of the European Southern Observatory.

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 such as the moon (unless a powerful artificial light source was placed on the surface of the moon to act as a reference). Only targets which are at temperatures of more than 1000 Centigrade are bright 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 angular sizes to be observed by the VLTI.

The VLT is operated by the European Southern Observatory.

Related topics

External links

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