Paranal Observatory

The Paranal Observatory is an astronomical observatory in the Atacama Desert in northern Chile, on the mountain Cerro Paranal. This is located about 120 km south of the city of Antofagasta and twelve miles from the Pacific coast. The observatory is operated by the European Southern Observatory ( ESO) and is the site of the Very Large Telescope ( VLT), the Very Large Telescope Interferometer (VLTI ) and the survey telescopes VISTA and VST. The atmosphere above the summit is characterized by dry and exceptionally smooth air flow, which makes the mountain at a very attractive location for an astronomical observatory. The summit was shut blown up in the early 1990s from its original height of 2660 m to 2635 m in order to create a plateau for the VLT.

  • 2.1 The appearance of the Unit Telescopes
  • 2.2 instruments
  • VST 4.1
  • 4.2 VISTA
  • 5.1 sequence of observations
  • 5.2 Monitoring the observation conditions

Logistics and Infrastructure at Paranal

Paranal is located far away from the main traffic routes. The observatory can be reached from Antofagasta only by a journey lasting several hours, with the last 60 km run on a tarmac runway, meanwhile, branched from the Panamericana. Accordingly, there is no supply lines to Paranal, all consumer products must be locally produced or held in stock. In addition to operation and maintenance of the telescopes that means the supply by an average of about 130 people who are constantly on the mountain.


In the environment of Antofagasta, there are several copper mines operating under similar conditions. Therefore, you had the complete infrastructure not build itself, but could select specialized utilities. Water is supplied daily as needed Tanker, about two to three times a day. Tankers bring fuel for the gas station the observatory own vehicles and the gas turbine to generate electricity. There are also three diesel generators, but these are only used during power outages. The vehicles are serviced locally. Scientific instruments require special cooling is required for the liquid nitrogen. An ESO own liquefaction plant was transported for 2006 by La Silla Paranal after liquid nitrogen was supplied in previous years from Antofagasta. Telecommunications, ie telephony, video calls and data traffic is delivered over a microwave radio link to Santiago, originally also moved from La Silla Paranal uplink station to a communications satellite has now been decommissioned.


Engineers and scientists are recruited both nationally and internationally in Chile, most of the member states of ESO. The official language is English, in addition to Spanish and spoken most other European languages. The Paranal employees either live or in Antofagasta, Santiago de Chile and eligible for layers of one to two weeks after Paranal. The transport costs are covered by ESO, the bay, the nearly two-hour flights between Santiago and Antofagasta by an external agency, but which maintains an office in the ESO office in Santiago. There is a daily transport from Antofagasta to Paranal and back by a chartered bus ride to raise additional observatory own SUV.


In addition to the telescopes and the VLTI laboratory, located on the plateau of the mountain, there are below the summit area nor a control building. All telescopes and the VLTI are controlled from a common control room, so that at night no one in the telescope field.

They are located in a base camp 200 m deeper, about five kilometers from the telescopes. From the original camp, which was made ​​up of mobile homes, parts are still used, most units are now but in the end finished in 2002 - also called Residencia - ESO Hotel. The ESO Hotel is half built into the mountain and kept in concrete in reddish color, which makes it visually melt into the desert. This includes accommodation, administration, canteen, relaxing rooms, a small swimming pool and two gardens that serve both the indoor climate of the ESO hotel as well as the psychological well -being housed.

Three more permanent buildings at the base camp serve as storage and Gymnasium ( Warehouse), as maintenance hangar for telescopes and instruments as well as for regular coating of the primary mirror of the telescope with aluminum (Mirror Maintenance Building, MMB), and as additional offices for engineers and technicians. For emergencies, there is a permanently staffed emergency room, an ambulance, a helicopter landing pad directly on base camp and a small airstrip at the foot of the mountain. In addition, the observatory maintains a small fire department. The construction of buildings and telescopes is designed so that a continuation of the operation even after massive earthquake is possible.

The streets of the observatory itself are paved to prevent dust that would interfere with the astronomical observations. In addition to the SUV and small car observatory internally can therefore be driven.

Astronomical darkness

Because the observatory must be dark at night, the ESO hotel has special dimming systems that close the skylights over the gardens and the canteen with the help of special curtains. All other windows and doors have blinds made ​​of heavy fabric or are obscured by night projectable wood panels.

As in the context of all optical observatories at night may only be driven with parking light, which is why most cars are decorated in white and have phosphorescent limit sticker. The road is marked by marker lights that charge during the day by solar panels. Footpaths in the telescope area are also painted with white color and with phosphorescent brands. Flashlights are inevitable especially during a new moon, but must not be directed towards the telescope in the summit area.


The investments of the entire VLT project amounted to over a period of 15 years to about 500 million euros. The sum includes personnel and operating expenses, for design and construction of the VLT, including the first generation of instruments, and of the VLTI and the first three years of scientific operation. From the individual instruments, for example, ISAAC has cost about 2.5 million euros, 3.5 million euros UVES. The far more complex VLTI instruments AMBER and MIDI cost each about six million euros. The instruments are partially developed and built entirely by ESO, but more often in cooperation with foreign institutions. In this case, the material costs are borne by the ESO, the personnel costs of the respective institutions that receive guaranteed observing time in return. The cost is taken into account that the ESO is also exempt as a supranational organization, like other international research centers from the taxes of the member countries. Material costs thus incurred without VAT, personnel costs partially, except that of the local employees in Chile, with no income tax.

The ongoing operation of all facilities in Chile, so La Silla, Paranal, the administration in Santiago and the beginning of the ALMA project in 2004 amounted to 30 million euros, the operating costs accounted for about half each on staff and. This sum represented a third of the total ESO- annual budget for 2004 of about 100 million euros, which includes not only Chile still operating the main institute in Europe and investment, mainly for ALMA.

The cost of the VLT project are thus a moderate to large space mission, for example, the Gaia spacecraft, comparable. Construction and launch of the Hubble Space Telescope (HST), however, have cost two billion dollars, almost four times the VLT. The annual operation of the HST is about eight times as expensive as that of the VLT, mainly because of the expensive service missions. The two telescopes of the Keck Observatory were funded by a private donation of around $ 140 million, the annual cost is about eleven million dollars. Since the Keck telescopes were built on the existing Mauna Kea Observatory, were there, however, to lower infrastructure costs.

Very Large Telescope

The Very Large Telescope ( VLT) is composed of four telescopes astronomical observatory reflector, whose levels can be connected together. The VLT is designed for observations in the visible light through to the mid-infrared. The telescopes can be connected together using the VLT Interferometer (VLTI ) for interferometry.

With the help of adaptive optics, it is at the telescopes of the Very Large Telescope (especially with the instrument NACO ) now managed to surpass the resolution of the Hubble Space Telescope (HST ). The advantage of the HST was since the early 1990s that his shots as opposed to ground-based telescopes by no disturbing atmosphere are also deteriorated. Using adaptive optics but this impairment was almost compensated in the wavelength region of the near infrared light now, so today's VLT images in the near- infrared ( approximately one to five microns wavelength) Hubble images with resolution of less than a tenth of an arc second part in no way inferior. In the optical spectral region that is not yet possible because the correction of atmospheric disturbances would occur more quickly by means of adaptive optics, as it is currently technically possible. With the VLTI significantly higher resolutions in the range of milli- arcseconds be achieved again.

The optics of the Unit Telescopes

The four large telescopes as Unit Telescopes (UT ) respectively. Unit has a telescope in his mount a floor area of ​​22 m × 10 m and a height of 20 m, with a movable weight of 430 tons. You are azimuthally mounted, essentially identical, Ritchey -Chrétien telescopes that can be operated as a Cassegrain, Nasmyth or Coudé telescope either. You have a main mirror diameter of 8.2 meters each and a secondary mirror of 1.12 meters. Thus, it was the largest one-piece astronomical mirror of the world until the Large Binocular Telescope was taken with 8.4 - meter mirror in operation. Even larger telescopes such as the Keck telescopes, have segmented mirrors. The main levels are too thin to stay in shape, moves the telescope, and are therefore corrected by active optics with the aid of hydraulic rams 150 about once per minute in shape.

The four primary mirror of the VLT were produced between 1991 and 1993 at the Mainz special glass from Schott AG in a developed especially for this project by centrifugal casting. After the actual casting and solidification of the glass composition, the mirror blanks were again thermally post, whereby the glass transforms into the glass ceramic Zerodur. In this production step, the material also gets its unusual property of zero thermal expansion. After a first machining the mirror substrate were transported by ship to the French company REOSC where the high-precision, two-year surface processing took place. The final mirror surface has an accuracy of a 50.000stel millimeters ( 8.5 nm is less than 1/30 of the wavelength with respect to 600 nm). Each UT has four focal points where instruments can be mounted, a Cassegrain and two Nasmythfoki. In addition, the telescopes have a Coudéfokus, can be fed through the light into the VLTI.

Astronomical mirrors can be cleaned only very limited because almost all cleaning techniques cause microscopic surface scratches that deteriorate the image quality. In addition to a monthly inspection, is dabbed gently at the loose dirt, the mirrors of the VLT are therefore mirrored every one to two years from scratch. To this end, the old mirror layer is removed with solvents and then a new mirror layer, usually aluminum vapor-deposited.

The individual UTs were in Mapudungun, the Mapuche language, Antu ( Sun), Kueyen baptized (Moon), Melipal ( Southern Cross ) and Yepun (Venus). The first mounted UT, Antu, delivered on 25 May 1998, the first images with a test camera, the scientific observation operation began on 1 April 1999.


The first generation of instruments consists of ten scientific instruments. This is to cameras and spectrographs for different spectral ranges. HAWK-I was not part of the original plan for the first generation, but replaced a contrast to the original plan is not built instrument NIRMOS. The design of the instruments was chosen so that they provide a wide array of scholars the opportunity to record data for a variety of objectives. It is foreseeable that members of the second generation of instruments will, however, focus on specific and of astronomers viewed as particularly important issues, such as gamma-ray bursts, or exoplanets.

Was between May 2003 and March 2005, starting with Kueyen, in addition, developed by ESO self adaptive optics MACAO (Multi Application Curvature Adaptive Optics) on all four telescopes in operation. This much sharper pictures or picture weaker light sources are again possible, but the field of view MACAO optics is limited to 10 seconds of arc. The adaptive optics must correct what would be much too fast for the heavy primary mirror seeing the high frequency of several hundred Hertz. Therefore, MACAO works behind the focus in the collimated part of the beam path with a plan 10 -cm mirror, which is mounted on 60 piezo elements. In principle, such an adaptive optics at each focus are used in practice use of the VLT instruments currently only SINFONI MACAO the technique, otherwise MACAO serves mainly the observations with the VLT Interferometer. Only future instruments are increasing the use of MACAO.

Since the Yepun telescope carries instruments with adaptive optics, the telescope is equipped with an artificial guide star, a " Laser Guide Star" ( LGS). A strong laser stimulates this sodium atoms at an altitude of about 95 km to the lights on, so that the light of this artificial star is affected in the same way on the way back to the telescope of the atmosphere, as the light of objects that are observed should. Instead of a possibly very faint object adaptive optics can then work with the help of artificial LGS.

Since April 2009, can also be measured with FORS2 polarization, since the polarimetric modes have been transferred from FORS1. FORS 1 has since merged with FORS 2 in one instrument.

Second generation instruments are under development or are already in use:

  • KMOS (K -band Multi -Object Spectrograph ) mainly for observation of distant galaxies.
  • MUSE ( Multi Unit Spectroscopic Explorer ) combines a wide viewing angle with high resolution using adaptive optics and covers a wide spectral range.
  • ESPRESSO ( Echelle Spectrograph for Rocky Exoplanet and Stable Spectroscopic Observations ) to search for rocky extra-solar planets in the habitable zone

VLT Interferometer

The Coudéfoki all telescopes can be combined with either incoherent or coherent. The common focus is incoherent in an underground plenum and is not currently used. The coherent focus is located in an adjacent laboratory and is fed by a special optical system, the VLT Interferometer (VLTI ). This is equivalently by interferometry, a radio astronomy interferometer, a far better resolution than achieved with only a telescope.

Main component of the system are variable in length six optical delay lines (English delay lines ). These same from the first, caused by their different locations transit time differences of the light between the individual telescopes. Second, they compensate for the geometric- projected optical path difference that arises when an object is not exactly at its zenith. Since this difference in length is changed by the apparent movement of the object in the sky, the delay lines have to be variable over a difference of up to 60 m, with an accuracy of much better than one quarter of the wavelength ( see below). The stability of the wave front is also of critical importance, therefore, stabilizes the adaptive optics system MACAO the beam paths of the UTs Coudéfokus before the light is passed to the delay lines. The image stabilization for the Auxiliary Telescopes ( " Auxiliary Telescopes ", see next paragraph) is done with a somewhat simpler system that makes only tip-tilt correction, ie corrected only tilts of the wavefront, but not its shape.

Four smaller 1.8 - m telescopes, the Auxiliary Telescopes ( " Auxiliary Telescopes ," ATs ), which are used exclusively for the interference fax and distance can be used for interference measurements up to 200 m are also installed. The most striking feature of the ATs is that they can be moved and installed on a total of 30 stations. To the AT stations are connected to rails. The light is passed in underground tunnels from the stations to the delay lines. The advantage of the idea of being able to operate the VLTI with both the UTs as with the ATs, is that the resolution is essentially determined by the distance between the telescopes, but the low-light performance when measuring objects from the telescope diameter. For many scientific problems the objects are bright enough to be measured by the ATs alone. The UTs can then be used for other research programs. Only for interferometry faint objects the UTs or a mixed configuration of UTs and ATs are necessary.

The VLTI saw his first light on 17 March 2001. At that time, two 40 - cm - Siderostate and a test instrument were installed. Since then, two scientific instruments and numerous support systems have been integrated into the system. Scientific operation was started in September 2003 with the first instrument, the MIDI. MIDI stands for "MID -infrared Interferometric instrument". It operates at wavelengths around 10 microns and can combine the light from two telescopes. The objective of the MIDI is less the creation of complete high-resolution images, as the determination of the apparent size and simple structure of the observed objects. Capturing images is in principle with the second instrument AMBER, possible. AMBER is the " Astronomical Multiple BEam Recombiner ". AMBER combines the optical paths of two to three telescopes. The device operates in the near infrared range at about 1-2 micrometers. However, this instrument will initially be used for tasks such as spatially highly resolved spectroscopy.

The simultaneous combination of all eight telescopes, ie the four UTs and four ATs is theoretically possible. In fact, the number of simultaneously usable telescopes is limited by two factors. First, of the eight planned delay lines currently only six realized. Second, the existing instruments can combine a maximum of three beam paths simultaneously. Instruments with further capabilities are discussed but for the second generation VLTI instrument.

Survey telescopes


The VLT Survey Telescope is a 2.6 -m Ritchey -Chrétien Cassegrain telescope with an f-number of 5.5. It is, like all other telescopes at Paranal, azimuthally mounted. VST only a single instrument, the OmegaCam with a large field of view of about 1 degree × 1 degree for images in the wavelength range 330 to 1000 nanometers. In 2001, the completed primary mirror was broken in the shipping to Chile, in June 2011 the first pictures were published. The VST will be used 100% in service mode (see the end of the observations).


The Visible & Infrared Survey Telescope for Astronomy is a 4 -meter telescope, also to the sky survey, but in the infrared region from 1 to 2.5 microns. His field of vision is also a square degree. It is not located on the main summit of Cerro Paranal, but on an approximately one kilometer away side peak, but is also controlled by the VLT control building. On 21 June 2008, the first test observation with IR camera system was successfully carried out. Since the main VISTA mirror is manufactured by the same manufacturer as the VST primary mirror, the local delay has had an impact on this project. VISTA was originally a British national project, but with the United Kingdom's accession to ESO and the decision to build VISTA at Paranal, astronomers will have access to this telescope world.

Watch at Paranal Observatory

Observation time can be applied twice a year for the next semester. Depending on the telescope is two to five times as much time as requested can actually be awarded. The proposals are weighted by a consultative group for scientific quality and urgency. After approval, the astronomer sets home yet determined the detailed sequence of observations in the so-called "Observing Blocks" (OBs ). Either only these OBs, together with the desired conditions of observation, sent for execution to Paranal, to the service mode observer, or the astronomer himself travels to Visitor -mode observations to Chile.

Sequence of observations

At the telescope are always an engineer who " Telescope and Instrument Operator" ( TIO ), and an astronomer who "Nighttime Astronomer " ( NA) of the ESO. In the service mode of the NA decides based on the observation conditions, which OBs can be performed with any prospect of success, and performs the observations together with the TIO, which is responsible for the telescope and the technical process. After the data is stored, the NA decides whether they meet the requirements of the applicant or whether the OB must be repeated. For the most part derived from the ESO member countries, working at Paranal astronomers determined not own scientific work, but rather the unwinding of " service programs " the everyday work on the other side.

At the visitor mode the visitor comes to the task to make critical decisions about the OBs that were not estimated in advance, so for example when highly variable objects are to be observed. A disadvantage of the visitors, however, has no influence on the weather conditions under which his program is carried out, since the observation dates are set for the Visitor mode about half a year before.

During the day, oversees a " Daytime Astronomer " typically two telescopes. He performs calibrations for the observations of last night, taking care of the solution possibly at night problems encountered and prepares the telescope to the next night before.

Monitoring of the conditions of observation

To have not only subjective impressions of the observation conditions by working at each of the telescopes, astronomers and engineers, a system for " Astronomical Site Monitoring " has been set up, which automatically receives the data and archived. In addition to numerous sensors to measure meteorological conditions such as air and soil temperature, humidity, wind speed and direction, and Staubteilchendichte also specifically astronomical parameters are measured. The " seeing " is measured by a small 35 -inch special Telescope, the DIMM, which performs throughout the night all about two minutes a measure of image quality. Instead of making a simple image and measure the size of the star shown, it compares the wavefront of two spaced apart about 20 cm sub- apertures, each with 4 cm diameter. This has the advantage to measure in addition to seeing the other, particularly interesting for the interferometric properties of the current turbulence in the atmosphere. The transparency of the atmosphere is measured in terms of the same image, only that instead of the image size of the incident flux of the star measured and compared with tabulated values ​​for a clear atmosphere.

A second instrument, the MASCOT (Mini All Sky Cloud Observation Tool), goes through a fish -eye lens shots of the entire sky, and allows an estimate of the cloud. In addition, ESO edited the current satellite data to provide the observers of the telescopes with information about the expected observation conditions.

Scientific Results

Since the beginning of the scientific operation of the VLT on April 1, 1999 to 2005, over 1000 articles have been published in peer-reviewed journals that are based on data from the Paranal Observatory. Among the key findings include:

  • The first direct images of exoplanets have been made with the VLT. While it is not quite sure whether this honor GQ Lupi b or the planet deserves 2M1207b, but both images are from NACO.
  • The Impact 's Deep was observed by all ESO telescopes from. In addition to pictures, new results have been obtained on the chemical composition of the comet Tempel 1 with spectrography.
  • With ISAAC the distance to the galaxy NGC 300 could be determined more accurately than any other galaxy outside the immediate vicinity of the Milky Way. Such distance determinations using the Cepheids are an important foundation of cosmic distance measurements.
  • The faint companion of AB Doradus was first directly imaged with NACO - SDI, enabling its mass could be determined with the help of Kepler's laws. This brown dwarf is twice as heavy as expected theoretically, which probably requires changes to the theory of the internal constitution of the stars and the frequency of planets and brown dwarfs.
  • By chance, a bright meteor crossed the field of FORS 1, as straight spectra were recorded. It is the first precisely calibrated spectrum of such a luminous phenomenon.
  • FORS and ISAAC 2 jointly hold the record for the most distant gamma-ray burst at z = 6.3.
  • With the VLTI not only the diameter but the shape of the star can be determined. While Eta Carinae seems drawn by its strong stellar wind over the poles in the length, Achernar is flattened by its rapid rotation to the limit of the theoretically possible.
  • For the first time with the VLTI an extragalactic object in the middle infrared region resolved by interferometry at 10 microns, the active nucleus of the galaxy NGC 1068th This Seyfert galaxy contains a black hole of about 100 million solar masses.
  • Based on an occultation by the moon, Charon Pluto on 11 July 2005 its exact diameter was determined to be 1207.2 km with the VLT first time. Also, the temperature could be measured with -230 ° C degrees, which is about 10 ° C colder than previously thought.
  • With the new NACO SDI ( NACO Simultaneous Differential Imager ) on the VLT in early 2006 was discovered a brown dwarf and a companion that are only 12.7 light-years away from Earth.
  • Through observations of the brown dwarf 2MASS1207 - 3932 with the VLT was discovered in May 2007 that the object has not only a revolving planet that was directly observed as the first exoplanet, but also how young stars from a disk of gas and dust is surrounded. In addition, astronomers were able to demonstrate that the brown dwarf also has a jet.
  • With the VLTI succeeded the star Theta 1 Ori C in the harness, so resolve the central region of the Orion Nebula, as the binary system to track the orbit between January 2007 and March 2008. Through various interconnections of three telescopes was used at a base length of 130 meters with VLTI / AMBER near-infrared (1.6 and 2.2 microns H- and K- band, ) reaches a resolution of 2 milliarcseconds.