Very Large Telescope 151648 212331466 2008-05-14T11:54:57Z 141.33.50.161 Fix redlink {{Refimprove|date=April 2008}} {{redirect|VLT}} {{Infobox Observatory |name = Very Large Telescope |image = [[Image:Very Large Telescope Array.aerial view.jpg|250px]] |caption = 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]]. |organization = [[European Southern Observatory | European Southern Observatory (ESO)]] |location = [[Cerro Paranal]], [[Atacama desert]], [[Chile]] |coords = {{coor dms|24|37|38|S|70|24|15|W|region:CL-AN_type:landmark_scale:2500}} |altitude = 2,635 m |weather = >340 clear nights/year |website = [http://www.eso.org/projects/vlt/ Very Large Telescope] |established = |closed = |telescope1_name = Antu (UT1) |telescope1_type = 8.2 m reflector |telescope2_name = Kueyen (UT2) |telescope2_type = 8.2 m reflector |telescope3_name = Melipal (UT3) |telescope3_type = 8.2 m reflector |telescope4_name = Yepun (UT4) |telescope4_type = 8.2 m reflector }} The '''Very Large Telescope''' ('''VLT''') is a system of four separate [[optical telescope]]s (the '''Antu telescope''', the '''Kueyen telescope''', the '''Melipal telescope''', and the '''Yepun telescope''') organized in an array formation. Each telescope has an 8.2 m aperture. The array is complemented by four movable Auxiliary Telescopes (ATs) of 1.8 m aperture. The VLT was built and is operated by the [[European Southern Observatory]] (ESO). The 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 (8.2 meter diameter) telescopes, and an [[astronomical interferometer]] (VLTI) which is used to resolve fine features. The interferometer also includes a set of four 1.8 meter diameter movable telescopes dedicated to interferometric observations. The 8.2 meter telescopes have been named after the names of some astronomical objects in the local [[Mapuche]] language: Antu (The [[Sun]]), Kueyen (The [[Moon]]), Melipal (The [[Crux|Southern Cross]]), and Yepun ([[Venus (planet)|Venus]]). The VLT 8.2 meter telescopes can be operated in three modes: * as a set of four independent telescopes (this is the primary mode of operation). With one such telescope, images of celestial objects as faint as magnitude 30 can be obtained in a one-hour exposure. This corresponds to seeing objects that are four billion (10<sup>9</sup>) times fainter than what can be seen with the unaided eye. * as a single large [[Coherence (physics)|coherent]] [[astronomical interferometer|interferometric instrument]] (the '''VLT Interferometer''' or '''VLTI'''), for extra resolution (this is occasionally used, only for observations of relatively bright sources). * as a single large incoherent instrument, for extra light-gathering capacity (this mode is not used for now, although multiple telescopes are sometimes independently pointed at the same object, either to increase the total light-gathering power, or to provide simultaneous observations with complementary instruments) The VLTs are equipped with a large set of instruments permitting observations to be performed from the near-UV to the mid-IR (ie a large fraction of the [[Infrared astronomy#Astronomers.27 Infrared Spectrum|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 at [[infrared]] wavelengths correct for the effects of the atmospheric turbulence, providing images almost as sharp as if the telescope were in space. In the near-IR, the Adaptive Optics images of the VLT are up to three times sharper than those of the [[Hubble Space Telescope]], and the spectroscopic resolution is many times better than Hubble. The VLTs are noted for their high level of observing efficiency and automation. The principal role of the main VLT telescopes is to operate as four independent telescopes. The interferometry (combining light from multiple telescopes) is used about 20 percent of the time for very high-resolution on bright objects. Additionally, the four 8.2m telescopes are accompanied by four smaller Auxiliary Telescopes of 1.8 m each (two operational in 2005, the other two in 2006), which can be placed on different positions around the four big telescopes in order to provide better interferometric observations. The VLT is operated by the [[European Southern Observatory]]. In [[2004]], VLT telescopes produced some of the first [[infrared]] images of [[extrasolar planets]] [[GQ Lupi b]] and [[2M1207b]]. Among the more recent discoveries is the discovery of the farthest gamma-ray burst and the evidence for a black hole at the centre of our Galaxy, the Milky Way. The VLT has also discovered the candidate farthest galaxy ever seen by humans, Abell 1835 IR1916. == Instruments == Instruments on the VLT<ref>[http://www.eso.org/sci/facilities/paranal-instr.html Paranal Observatory Instrumentation]</ref>: {| class="wikitable" |+ Instruments on the VLT |- ! Telescope ! Cassegrain-Focus ! Nasmyth-Focus A ! Nasmyth-Focus B |- ! Antu (UT1) | FORS&nbsp;2 | ''CRIRES'' | ISAAC |- ! Kueyen (UT2) | FORS&nbsp;1 | FLAMES | UVES |- ! Melipal (UT3) | VISIR | Guest focus | VIMOS |- ! Yepun (UT4) | SINFONI | ''HAWK-I'' | NACO |} ;FORS&nbsp;1 :('''FO'''cal '''R'''educer and low dispersion '''S'''pectrograph) is a visible light camera and Multi Object Spectrograph with a 6.8 [[arcminute]] field of view. ;FORS&nbsp;2 :Like FORS&nbsp;1, but with further multi-object spectroscopy. ;ISAAC :('''I'''nfrared '''S'''pectrometer '''A'''nd '''A'''rray '''C'''amera) is a near infrared imager and spectrograph ;UVES :('''U'''ltraviolet and '''V'''isual '''E'''chelle '''S'''pectrograph) is an [[ultraviolet]] and visible light spectrograph. ;FLAMES :('''F'''ibre '''L'''arge '''A'''rea '''M'''ulti-'''E'''lement '''S'''pectrograph) is a multi-object fibre feed unit for UVES and GIRAFFE, the latter allowing the capability for simultaneously studying hundreds of individual stars in nearby galaxies at moderate spectral resolution in the visible. ;NACO :'''NA'''OS-'''CO'''NICA, (NAOS meaning '''N'''asmyth '''A'''daptive '''O'''ptics '''S'''ystem and CONICA meaning '''CO'''ude '''N'''ear '''I'''nfrared '''CA'''mera) is an [[adaptive optics]] facility which produces infrared images as sharp as if taken in space and includes spectroscopic, polarimetric and coronagraphic capabilities. ;VISIR :(VLT spectrometer and imager for the mid-infrared) provides diffraction-limited imaging and spectroscopy at a range of resolutions in the 10 and 20 micron mid-infrared (MIR) atmospheric windows. ;SINFONI :is a medium resolution, near-infrared (1-2.5 microns) integral field spectrograph fed by an adaptive optics module. ;CRIRES :('''CR'''yogenic '''I'''nfra'''R'''ed '''E'''chelle '''S'''pectrograph) is adaptive optics assisted and provides a resolving power of up to 100 000 in the infrared spectral range from 1 to 5 microns. ;HAWK-I :('''H'''igh '''A'''cuity '''W'''ide field '''K'''-band '''I'''mager) is a near-infrared imager with a relatively large field of view. ;VIMOS :('''VI'''sible '''M'''ulti-'''O'''bject '''S'''pectrograph) delivers visible images and spectra of up to 1000 galaxies at a time in a 14 x 14 arcmin field of view. ;Guest focus :Available for visitor instruments, such as ULTRACAM or DAZZLE. Several second-generation VLT instruments are now under development: ;X-Shooter :(a wide-band [UV to near infrared] spectrometer) designed to explore the properties of rare, unusual or unidentified sources; ;KMOS :(a cryogenic infrared multi-object spectrometer) intended primarily for the study of distant galaxies; ;MUSE :(a huge ‘3-dimensional’ spectroscopic explorer) which will provide complete visible spectra of all objects contained in ‘pencil beams’ through the Universe; ;SPHERE :(a high-contrast adaptive optics system) dedicated to the discovery and study of exoplanets. ==Interferometry and the VLTI== In its interferometric operating mode, the light from the telescopes is reflected off mirrors and directed through tunnels to a central beam combining laboratory. The VLTI is intended to achieve an effective [[angular resolution]] of 0.002 [[arcsecond]] at a [[wavelength]] of 2 [[µm]]. This is comparable to the resolution achieved using other arrays such as the [[Navy Prototype Optical Interferometer]] and the [[CHARA array]]. Using the big telescopes the faintest object the VLTI can observe is [[apparent magnitude|magnitude]] 7 in the near infrared for broadband observations[http://www.eso.org/instruments/amber/], similar to many other near infrared / optical interferometers without fringe tracking<SUP>[[List of astronomical interferometers at visible and infrared wavelengths|2]]</SUP>. At more challenging mid-infrared wavelengths, the VLTI can reach magnitude 4.5, significantly fainter than the [[Infrared Spatial Interferometer]]. When fringe tracking is introduced, the limiting magnitude of the VLTI is expected to improve by a factor of almost 1000, reaching a magnitude of about 14. This is similar to what is expected for other fringe tracking interferometers. In spectroscopic mode, the VLTI can currently reach a magnitude of 1.5. The VLTI can work in a fully integrated way, so that interferometric observations are actually quite simple to prepare and execute. The VLTI has become worldwide the first general user optical/infrared interferometric facility offered with this kind of service to the astronomical community<sup>[http://www.eso.org/sci/publications/messenger/archive/no.119-mar05/The-Messenger-119-willkVLTI.html]</sup>. Because of the many mirrors involved in the VLTI system, about 99 percent of the light is lost before reaching the detector. Additionally, the interferometric technique is such that it is very efficient only of objects that are small enough that all their light is concentrated. For instance, an object with a relatively low [[surface brightness]] such as the moon cannot be observed, because its light is too diluted. Only targets which are at temperatures of more than 1000°[[Celsius|C]] have a [[surface brightness]] high enough to be observed in the mid-infrared, and objects must be at several thousands of degrees Celsius for near-infrared observations using the VLTI. This includes most of the stars in the solar neighborhood and many extragalactic objects such as bright [[active galactic nucleus|active galactic nuclei]], but this sensitivity limit rules out [[interferometry|interferometric]] observations of most solar-system objects. 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 nucleus|active galactic nuclei]]. Because the Unit Telescopes are used most of the time independently,they are used in the interferometric mode mostly during bright time (that is, close to Full Moon). At other times, [[astronomical interferometer|interferometry]] is done using 1.8 meter Auxiliary Telescopes (ATs), which are dedicated to full-time interferometric measurements. The first observations using a pair of ATs were conducted in February 2005, and all the four ATs have now been commissioned. For interferometric observations on the brightest objects, there is little benefit in using 8 meter telescopes rather than 1.8 meter telescopes. The first two instruments at the VLTI were VINCI (a test instrument used to set-up the system) and MIDI, which only allowed two telescopes to be used at any one time. With the installation of the three-telescope AMBER [[closure-phase]] instrument in 2005, the first imaging observations from the VLTI are expected soon. In 2008 the PRIMA instrument will further enhance the imaging capabilities of the VLTI by allowing phase-referenced imaging. 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.'' This involves additional effort concentrated on more rapid improvements to fringe tracking and the performance of the main [[Optical cavity#Optical Delay Line|delay lines]]. Note that this only applies to the interferometer and not other instruments on Paranal. In 2005, the VLTI was routinely producing observations, although with a brighter limiting magnitude and poorer observing efficiency than expected. As of March 2008, the VLTI had already led to the publication of 89 peer-reviewed publications <ref>[http://archive.eso.org/wdb/wdb/eso/publications/form ESO Telescope Bibliography]</ref>. ==References== {{reflist}} ==See also== * [[List of observatories]] * [[List of optical telescopes]] * [[List of largest optical reflecting telescopes]] * [[List of astronomical interferometers at visible and infrared wavelengths]] * [[Extremely Large Telescope]] * [[Giant Magellan Telescope]] ==External links== *[http://www.eso.org/paranal/site/visitors/tourist.html Visits to the Paranal Site] *[http://www.eso.org/projects/vlt/ ESO VLT] official site for the 8m telescopes. *[http://www.eso.org/projects/vlti/ ESO VLTI] official site for the interferometer (combining the telescopes) *[http://www.dutchspace.nl/pages/business/content.asp?id=176&P=1_3_17 Delay Lines for the Very Large Telescopes] @Dutch Space *[http://www.tno.nl/content.cfm?&context=markten&content=case&laag1=191&item_id=583&Taal=2 The VLTI Delay Lines] @TNO *[http://www.millhouse.nl/vlt.html The VLTI Delay Line] Article and images by Fred Kamphues/Mill House Engineering *[http://www.tno.nl/content.cfm?&context=markten&content=case&laag1=191&item_id=586&Taal=2 The PRIMA Star Separator] *[http://www.stecf.org/astrovirtel/ ASTROVIRTEL ''Accessing Astronomical Archives as Virtual Telescopes''] including archives from the VLT *[http://www.smh.com.au/articles/2002/11/24/1037697982142.html Telescope to challenge moon doubters] -- note description of VLTI capabilities is inaccurate *[http://volker.umpfenbach.de/en/reisen/2003suedamerika/2003suedamerika09d.htm Travelogue VLT Visit] *[http://gallery.hd.org/_virtual/ByCategory/natural-science/vlt/ VLT images] [[Category:Science and technology in Chile]] [[Category:Telescopes]] [[Category:Interferometric telescopes]] [[Category:buildings and structures in Antofagasta Region]] [[fa:تلسکوپ وی ال تی]] [[cs:Very Large Telescope]] [[de:Paranal-Observatorium]] [[es:Very Large Telescope]] [[fr:Very Large Telescope]] [[it:Very Large Telescope]] [[nl:Very Large Telescope]] [[pl:VLT]] [[pt:Very Large Telescope]] [[sv:Very Large Telescope]] [[zh:甚大望远镜]]