Paranal observatory

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The Cerro Paranal plateau with the Very Large Telescope; from front to back: the control building below the plateau, the smaller domes of the four auxiliary telescopes, the domes from UT1 to UT4: Antu, Kueyen, Melipal and Yepun; the smaller dome of the VST. On the summit behind the building of the VISTA.

The Paranal Observatory is an astronomical observation station in the Atacama Desert in northern Chile , on the Cerro Paranal mountain . This is about 120 km south of the city of Antofagasta and 12 km from the Pacific coast. The observatory is operated by the European Southern Observatory (ESO) and is the location 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 a dry and exceptionally calm air flow, which makes the mountain a very attractive location for an observatory . In order to create a plateau for the VLT, the summit was demolished in the early 1990s by blasting from 2660  m to 2635  m .

Logistics and infrastructure on Paranal

The Paranal observatory at sunrise, top left Cerro Paranal with the VLT, top center the VISTA survey telescope, bottom left the ESO Hotel , center and bottom right the old base camp

Paranal is far from the main traffic routes. The observatory can only be reached from Antofagasta by a drive of several hours, with the last approx. 60 km leading over a paved slope that branches off from the Panamericana . There are no supply lines to Paranal. All goods for the operation and maintenance of the telescopes as well as for the approximately 130 people on average who are constantly on the mountain must be produced locally or kept in stock.


There are several copper mines in the Antofagasta area that work under similar conditions. Therefore, you did not need to build the infrastructure yourself, but could commission specialized supply companies. Water is delivered daily by tanker trucks as needed , around two to three times a day. Tanker trucks also bring fuel for the filling station of the observatory's own vehicles and, by the end of 2017, for the gas turbine to generate electricity. There were also three diesel generators, which were only used in the event of a power failure. The observatory has been directly connected to the Chilean power grid since December 2017. The vehicles are serviced locally. The scientific instruments require special cooling, for which liquid nitrogen is required. ESO's own liquefaction plant was transported from La Silla to Paranal in 2006 , after liquid nitrogen had been delivered from Antofagasta the years before. Telecommunications, d. H. Telephony , video calls and data traffic , was initially a relocated from La Silla to Paranal uplink station to a communications satellite then, a microwave - radio link provided to Antofagasta. A fiber optic cable laid to Antofagasta in 2010 finally provided a connection with a data rate of 10 Gbit / s, which was required for the survey telescopes.


Engineers and scientists are recruited both nationally in Chile and internationally, mostly from the member countries of the ESO . The official language is English , but Spanish and most other European languages ​​are also spoken. The employees on Paranal live either in Antofagasta or in Santiago de Chile and come to Paranal for shifts of one to two weeks. There is a daily transport from Antofagasta to Paranal and back by a chartered bus, if necessary, the observatory's own 4x4 vehicles drive .


The ESO Hotel with its garden, swimming pool and the blackout curtain under the dome
The Mirror Maintenance Building, with two primary mirror cells, one with a protective cover, the other on an air cushion transporter, which can also be used to slide it into the telescope. On the left in the background the Paranal Plateau; Part of the road transporter for the mirror cells can be seen in the right foreground

In addition to the telescopes and the VLTI laboratory, which are located on the plateau of the mountain, there is also a control building below the summit area. All telescopes and the VLTI are controlled from a common control room so that nobody has to be in the telescope area at night.

The accommodations are located in a base camp 200 m below, about 5 km from the telescopes. From the original camp, from mobile homes was built parts are still used, most accommodations are now but in the end finished in 2002 - also Residencia mentioned - ESO Hotel . The ESO Hotel is half built into the mountain and made of concrete in a reddish color, which visually merges with the desert. This houses accommodation, administration, canteen, relaxation rooms, a small swimming pool and two gardens, which serve both the indoor climate of the ESO hotel and the mental well-being.

Three other permanent buildings in the base camp serve as a warehouse and sports hall (warehouse), as a maintenance hall for telescopes and instruments as well as for regular coating of the main mirrors of the telescopes with aluminum (Mirror Maintenance Building, MMB), and as additional offices for engineers and technicians. For emergencies there is a permanently manned emergency room, an ambulance, a helipad right at the base camp and a small runway at the foot of the mountain. The observatory also has a small fire department . The construction of the buildings and telescopes is designed so that operations can continue even after a severe earthquake .

The streets of the observatory itself are paved to avoid dust that would hinder astronomical observations. In addition to off-road vehicles, small cars can therefore also be driven inside the observatory .

Astronomical darkness

Because the observatory has to be dark at night, the ESO Hotel has special blackout 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 covered at night by sliding wooden panels.

As in the vicinity of all optical observatories, it is only allowed to drive with parking lights at night , which is why most vehicles are kept in white and have phosphorescent limitation stickers. The road is marked by marker lights that are charged by solar cells during the day . Footpaths in the telescope area are also painted white and have phosphorescent marks. Flashlights are unavoidable, especially when there is a new moon , but must not be pointed towards the telescope in the summit area.


The investments of the entire VLT project amounted to around 500 million euros over a period of 15 years . The sum includes personnel and material costs for the design and construction of the VLT, including the first generation of instruments, and the VLTI as well as the first three years of scientific operation. For example, ISAAC cost around 2.5 million euros of the individual instruments and UVES 3.5 million euros. The much more complex VLTI instruments AMBER and MIDI each cost around six million euros. Some instruments are completely developed and built by ESO, but more often in cooperation with external institutes. In this case, the material costs are borne by the ESO, the personnel costs by the respective institutes, who receive the guaranteed observation time in return.

The ongoing operation of all facilities in Chile, i.e. La Silla, Paranal, the administration in Santiago and the beginning ALMA project, amounted to 30 million euros in 2004, half of which was accounted for by personnel and operating costs. This sum corresponded to a third of the total ESO annual budget for 2004 of around 100 million euros, which, in addition to Chile, also includes the operation of the main institute in Europe and investments, mainly for ALMA.

The costs of the VLT project are thus comparable to a medium to large space mission, for example the Gaia space probe. In contrast, the construction and launch of the Hubble Space Telescope (HST) cost two billion US dollars , almost four times the VLT. The annual operation of the HST is about eight times more expensive than that of the VLT, mainly because of the expensive service emissions. The two telescopes of the Keck Observatory were financed by a private foundation of about $ 140 million, the annual cost is about $ 11 million. Since the Keck telescopes were built on the already existing Mauna Kea observatory , the infrastructure costs were lower there.

Very Large Telescope

Antu, one of the four unit telescopes. The three astronomers standing next to it enable a size comparison.
Image taken inside the open dome of a unit telescope. The telescope (right) is directed towards the zenith: Above the secondary mirror (M2), below it the Serruier tube , to the left of it, at the Nasmyth focus, the ISAAC instrument

The Very Large Telescope (VLT) is a large astronomical telescope consisting of four individual telescopes, the mirrors of which can be interconnected. The VLT is designed for observations in visible light up to mid- infrared . The telescopes can be connected together for interferometry using the VLT Interferometer (VLTI) .

With the help of adaptive optics, the telescopes of the Very Large Telescope (especially with the NACO instrument) have succeeded in exceeding the resolution of the Hubble Space Telescope (HST). The advantage of the HST since the early 1990s has been that, in contrast to earth-based telescopes, its recordings are not additionally impaired by any disturbing atmosphere . With the help of adaptive optics , this impairment could now be almost compensated in the wavelength range of near-infrared light, so that today's VLT recordings in the near-infrared (1 to 5 µm wavelength) Hubble images with a resolution of less than 0.1 ", sometimes in In the visible spectral range this is not yet possible, as the correction of atmospheric disturbances by means of adaptive optics would have to be carried out faster than is currently technically possible. With the VLTI, significantly higher resolutions in the range of milli-arcseconds are achieved.

The optics of the unit telescopes

One of the four main mirrors M1, the Nasmyth mirror M3, is mounted on the tower that rises in the middle; The mirror image of the secondary mirror M2 can be seen below it

The four large telescopes are called Unit Telescopes (UT). A unit telescope in its mount has a base area of ​​22 m × 10 m and a height of 20 m, with a movable weight of 430 tons. They are azimuthally mounted , essentially identical, Ritchey-Chrétien telescopes , which can be operated either as Cassegrain , Nasmyth or Coudé telescopes . They each have a primary mirror diameter of 8.2 m and a secondary mirror of 1.12 m. These were the largest astronomical mirrors in the world made from one piece until the Large Binocular Telescope with 8.4 meter mirrors was put into operation. Even larger telescopes, such as the Keck telescopes , have segmented mirrors . The main mirrors are too thin to keep their shape when the telescope is moving and are therefore corrected in their shape about once per minute by active optics with the help of 150 hydraulic rams.

The four main mirrors of the VLT were manufactured between 1991 and 1993 at the Mainz-based special glass company Schott AG using a centrifugal casting process specially developed for this project . After the actual casting and solidification of the glass mass, the mirror blanks were thermally post-treated again, which transforms the glass into the Zerodur glass ceramic . In this production step, the material also receives its extraordinary property of zero thermal expansion. After an initial processing, the mirror carriers 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 8.5 nm (λ / 70 at 600 nm). Each UT has four focal points to which instruments can be mounted, a Cassegrain focus and two Nasmyth focuses . In addition, the telescopes have a coudé focus , via which light can be fed into the VLTI.

Astronomical mirrors can only be cleaned to a very limited extent, as almost all cleaning techniques cause microscopic surface scratches that degrade the image quality. In addition to a monthly inspection, during which loose dirt is carefully dabbed off, the mirrors of the VLT are therefore re-mirrored every one to two years. To do this, the old mirror layer is removed with solvents and then a new mirror layer, usually aluminum, is vapor-deposited.

The individual UTs were baptized in Mapudungun , the language of the Mapuche , Antu ( sun ), Kueyen ( moon ), Melipal ( southern cross ) and Yepun ( Venus ). The first mounted UT, Antu, delivered the first images with a test camera on May 25, 1998; scientific observation began on April 1, 1999; the fourth UT, Yepun, began first observations on September 3, 2000.

Mirror of a unit telescope
mirror Main mirror M1 Secondary mirror M2 Nasmyth mirror M3
material Zerodur beryllium Zerodur
diameter 8.20 m 1,116 m 1.242 m × 0.866 m elliptical
thickness 178 mm 130 mm 140 mm
Weight 23,000 kg 44 kg 105 kg
shape concave convex plan
Radius of curvature 28.975 m -4.55 m
Optical data from a unit telescope
focus Cassegrain focus Nasmyth focus Coude focus
Focal length 108.827 m 120,000 m 378,400 m
corresponding ... 0.527 mm / " 0.582 mm / " 1.834 mm / "
Focal ratio f /  13.41 f /  15 f /  47.3
Facial field 15 ' 30 ' 1'


The 4LGSF operated at the Yepun telescope to generate four artificial guide stars at an altitude of 95 km by means of yellow laser light, which stimulates the sodium atoms present there to glow

The first generation of instruments consists of ten scientific instruments. These are cameras and spectrographs for different spectral ranges. HAWK-I was not part of the original plan for the first generation, but replaced an instrument that was not built, NIRMOS, contrary to the original plan. The design of the instruments was chosen in such a way that they offer a wide range of scientists the possibility of collecting data for the most varied of purposes. It is foreseeable that parts of the second generation of instruments, on the other hand, will concentrate on specific problems that astronomers consider particularly important, for example gamma-ray bursts or exoplanets .

Between May 2003 and March 2005 was started Kueyen, in addition to self-developed by ESO adaptive optics MACAO ( M ulti A pplication C urvature A daptive O ptics) on all four telescopes in operation. With this, much sharper images or images of weaker light sources are possible, but the field of view of the MACAO optics is limited to 10 ". The adaptive optics have to correct the seeing with a high frequency of a few hundred Hertz, which is much too fast for the heavy main mirror That is why MACAO works behind the focus in the collimated part of the beam path with a flat 10 cm mirror, which is mounted on 60 piezo elements. In principle, such adaptive optics can be used at every focus, in practice it is used by the VLT -Instruments currently only SINFONI use the MACAO technology, otherwise MACAO is mainly used for observations with the VLT interferometer. Only future instruments will increasingly use MACAO.

For adaptive optics, relatively bright guide stars are required in the observation area in order to determine the seeing. In order to use the existing natural SINFONI even with non guide stars, the Yepun telescope is provided with a laser for projecting an artificial guide star equipped, the " L aser G uide S tar" (LGS). This technology was supplemented in 2016 by a system for 4 guide stars, the 4LGSF, which, with special adaptive optics (GRAAL and GALACSI), is intended to improve the resolution of HAWK-I and MUSE as well.

Instruments at the VLT
telescope Cassegrain focus Nasmyth focus A. Nasmyth focus B
FORS2 CRIRES Guest focus
The Focal Reducer and low dispersion Spectrograph 2 is the sister instrument of the largely identical FORS1. With ISAAC and UVES, both were among the first four instruments in operation. FORS2 is also a camera in the visual spectral range with a large field of view of up to 6.8 '× 6.8'. In this field, instead of taking a picture, several objects can be spectroscoped at the same time with low resolution (MOS: Multi Object Spectroscopy). The MOS capability comes about through masks also used at VIMOS, into which the spectroscopy gaps are milled using laser technology.

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

The Cryogenic High-Resolution IR Echelle Spectrograph records high-resolution spectra in the wavelength range from 1 to 5 µm. The instrument was installed and tested in 2006 and has been in regular operation since April 1, 2007.

It was dismantled in 2014 to make improvements to the device and is expected to be operational again in 2018.

The guest focus offers scientists the opportunity to use their own and particularly specialized instruments on a telescope of the 8-meter class without having to meet all the specifications that a general ESO instrument is subject to. Up until now, the ULTRACAM was installed there, an instrument that can take images of a small field of view in a few arcseconds within milliseconds. The scientific goal of the ULTRACAM, which has already been mounted on other telescopes, is to record changes in the shortest time scales, such as those that occur in pulsars and black holes .
The Nasmyth Adaptive Optics S ystem- Coude Near Infrared Camera was taken over by the UT4 ​​in 2014. The K band M Ultimatum O bject S pectrograph is mainly used for observation of distant galaxies since the year 2013 in the scientific operation and will.
The instrument FORS1 mounted at this focus is a simplified version of the FORS2 and was merged with it in 2009 and mounted in its place on UT1. The Fiber Large Area Multi-Element Spectrograph is a spectrograph which, with the help of the glass fibers, can spectroscopically up to 130 objects in the field of view simultaneously with medium resolution (MEDUSA mode). In two other modes, IFU and ARGUS, the fibers are packed so close together that spatially resolved spectra of the objects with an apparent size of just a few arc seconds are possible. Alternatively, eight fibers can direct the light to UVES for high resolution spectroscopy. The Ultraviolet and Visual Echelle Spectrograph is a high-resolution spectrograph with a blue and a red optimized optical arm that can be operated simultaneously. The accessible wavelength range is from 0.3 to 1.1 µm.
The XSHOOTER instrument is the first of the second generation of instruments. XSHOOTER is a medium resolution spectrograph over a wide range of wavelengths from near ultraviolet to near infrared, from 0.3 to 2.5 µm, in a single image.
The VLT Imager and Spectrometer in the Infra Red , for images and spectra of weak objects in the mid-infrared range, from 8 to 13 and 16.5 to 24.5 µm. VISIR is therefore the instrument at the VLT that can go furthest into the infrared range. The Infrared Spectrometer And Array Camera can record images and slit spectra of low to medium resolution in the near infrared range . For this purpose, the instrument has two independent optical paths (“arms”), each of which is optimized for the wavelength ranges from 1 to 2.5 and from 3 to 5 µm. The Visible Multi-Object Spectrograph . The capabilities for spectroscopy and image acquisition are similar to those of the FORS2, but with a four times larger field of view totaling 4 × 7 '× 8'. MOS masks are punched with a laser machine, the Mask Manufacturing Unit (MMU), which also produces the masks for FORS2. There are also fiber bundles for integral field spectroscopy. A total of up to 6400 spectra can be recorded simultaneously with VIMOS.
The S pectro- P olarimetric H igh-Contrast E xoplanet RE search is a tool for discovery and study of exoplanets, which was taken in 2014 in operation.
The Spectrograph for Integral Field Observation in the Near-Infrared is a near-infrared spectrograph at 1 to 2.5 µm. The actual spectrograph SPIFFI (Spectrometer for Infrared Faint Field Imaging) records a spectrum of the entire field of view that can be 8 "× 8", 3 "× 3" or 0.8 "× 0.8" in size. The adaptive optics in the SINFONI module allow spectra to be recorded with the highest spatial resolution. The High Acuity Widefield K-band Imager , an instrument that covers the need for images with a large field of view with high spatial resolution in the near infrared range of 0.85 to 2.5 µm. HAWK-I had its First Light on August 1, 2007, and scientific operation started on April 1, 2008 (officially October 1, 2008). Actually NAOS-CONICA, where NAOS stands for Nasmyth Adaptive Optics S ystem and CONICA for Coude Near Infrared Camera . CONICA was originally intended for the coudé focus. NAOS is a system for image enhancement with adaptive optics, CONICA an infrared camera and spectrograph in the range from 1 to 5 µm. The difference to ISAAC is the excellent image quality, albeit with a smaller field of view. In addition, CONICA can record polarimetric measurements and mask out bright objects using coronography . With SDI, the Simultaneous Differential Imager in NACO, four images can be recorded simultaneously in four slightly different wavelength ranges. These images can be offset against one another in such a way that the differences also enable the detection of very faint objects in the presence of a lighter one.
The Multi Unit Spectroscopic Explorer combines a wide viewing angle with a high resolution through adaptive optics and covers a wide spectral range.

Second generation instruments are under development:

  • ESPRESSO ( E chelle SP ectrograph for R ocky E xoplanet- and S table S pectroscopic O bservations) for the search for rocky extra-solar planets in the habitable zone

VLT interferometer

Aerial view of the Paranal plateau. In the middle of the picture the building of the VLTI laboratory, above the four unit telescopes (UT), including two auxiliary telescopes (AT) and the right-angled rail system over which the ATs can be moved. The ATs can be connected to the VLTI at the round stations that can be reached via the rail system.
Delay lines of the VLTI, implemented by retroreflectors that can be moved on rails.
Interferometric recording using PIONIER and RAPID of a dust disk around a 4000 light-years distant binary star system
IRAS 08544-4431 ; the side length of the image corresponds to 0.6 arc seconds .

The coudé foci of all telescopes can be combined either incoherently or coherently . The common incoherent focus is in an underground collection space and is currently not in use. The coherent focus is located in an adjacent laboratory and is fed by a special optical system, the VLT interferometer (VLTI). With this, interferometry , equivalent to a radio astronomical interferometer , achieves a far better resolution than with just a telescope.

The main component of the system are six variable-length optical delay lines . Firstly, these compensate for the differences in transit time of the light between the individual telescopes due to their different locations. Second, they compensate for the geometrically projected difference in the optical path that occurs when an object is not exactly at its zenith . Since this difference in length changes due to the apparent movement of the object in the sky, the delay lines must be variable over a difference of up to 60 m, with a precision of significantly better than a quarter of the wavelength (see below). The stability of the wavefront is also of critical importance, which is why the MACAO adaptive optics system stabilizes the beam paths of the UTs in coudé focus before the light is directed to the delay lines.

In addition to the UTs, four smaller telescopes, which are exclusively intended for the interferometer, can be used, the so-called auxiliary telescopes ("auxiliary telescopes", ATs) with a 1.8 meter diameter Zerodur main mirror. They were installed between 2004 and 2006. Due to the smaller main mirror, a simple tip-tilt correction (STRAP) is sufficient for image stabilization in good seeing . In order to be able to use them beyond that, the simple adaptive optics system NAOMI, available from 2016-2017, is used. The most distinctive feature of the ATs is that they can be moved and installed on a total of 30 stations and can thus be used for interference measurements at a distance of up to 200 m. For this purpose, the AT stations are connected with rails. The light is directed from the stations to the delay lines in underground tunnels. The advantage of the idea of ​​being able to operate the VLTI with both the UTs and the ATs is that the resolution is largely determined by the distance between the telescopes, but the performance when measuring faint objects is determined by the telescope diameter. For many scientific questions, the objects are bright enough to be measured with the ATs alone. The UTs can then be used for other research programs. The UTs are only necessary for the interferometry of weak objects.

The VLTI saw its first light on March 17, 2001. At that time, two 40 cm siderostats and a test instrument were installed. Since then, two scientific instruments and numerous support systems have been integrated into the system. Scientific operations began in September 2003 with the first instrument, the MIDI. MIDI stands for " MID -infrared I nterferometric instrument ". It works at wavelengths around 10 µm and can combine the light from two telescopes. The aim of MIDI is less to generate high-resolution images than to determine the apparent size and simple structures of the objects being observed. In principle, it is possible to take pictures with the second instrument, AMBER. AMBER is the " A stronomical M ultiple BE on the R ecombiner ". AMBER combines the beam paths of two to three telescopes. The device works in the near infrared range between 1 and 2 µm. However, this instrument will also initially be used for tasks such as spatially highest-resolution spectroscopy. An interferometer specializing in high-resolution images has been located at the “visitor focus” of the VLTI since October 2010, and is intended for short instrument projects. The " P recision I ntegrated O ptics N ear-infrared I maging E xpe R iment" (PIONEER) was built by the University of Grenoble and installed and has created since the start among other images of multiple star systems. GRAVITY, in operation since the beginning of 2016, uses precise laser metrology to measure astrometric distances with an accuracy of around 10 µas (micro-arcseconds) and can also record high-resolution images in the near-infrared range. MATISSE, which saw its first light at the beginning of March 2018, creates images and spectra in thermal infrared and will replace MIDI. Both new devices can routinely connect all four large telescopes.

The simultaneous combination of all eight telescopes, i.e. the four UTs and four ATs, is theoretically possible. In fact, the number of telescopes that can be used at the same time is limited by two factors. Firstly, of the eight planned delay lines, only six have been implemented at present; secondly, the existing instruments can combine a maximum of four beam paths at the same time.

Survey telescopes

The VST with the dome open and the lock of the 2.6 meter diameter mirror open.


The V LT S urvey T elescope is a 2.6-meter Ritchey-Chrétien telescope with an aperture ratio of f /  5.5. Like all other telescopes on Paranal, it is mounted azimuthally. The VST has only one instrument, the OmegaCam with a large field of view of around 1 ° × 1 ° for images in the wavelength range from 0.33 to 1 µm. In 2001 the completed main mirror broke on the sea transport to Chile, in June 2011 the first pictures were published. The VST is used 100 percent in service mode (see under the observation sequence ).

The VISTA telescope with a main mirror measuring 4 meters in diameter


The V isible & I nfrared S urvey T elescope for A stronomy is a 4-meter telescope, also to the sky survey, but in the infrared region of 1 to 2.5 microns. Its field of view is also one square degree. It is not located on the main summit of Cerro Paranal, but on a side summit about 1 km away, but is also controlled from the VLT control building. On June 21, 2008, the first test observation with an IR camera system was successfully carried out. Since the VISTA main mirror is made by the same manufacturer as the VST main mirror, the delay there also affected this project.

VISTA was originally a UK national project but with the UK joining ESO and the decision to build VISTA on Paranal, astronomers around the world have gained access to this telescope.


NGTS building, the VLTs (left) and VISTA (right) in the background

The N ext G eneration T ransit S urvey is a device for sky survey with the aim Exoplaneten with a two to eight times the diameter of the earth by the Transit method , that is based on apparent brightness changes in the central star when pulled by the planet to discover.

The picture inside the building shows some of the twelve automatically operating telescopes

The device consists of 12 automatically working telescopes with a mirror diameter of 20 cm, each of which can cover a region of the sky with a diameter of a little more than 3 °, a total of 96 square degrees . The telescopes are commercially available astrographs with an improved lens hood , which reach the large image field through a hyperbolic mirror followed by a three- lens corrector . A CCD camera which is sensitive in the wavelength range from 600 to 900 nm and has a resolution of 4 million pixels is connected to it.

Although the focus is on smaller planets, NGTS is based on the concept of SuperWASP and the lessons learned from it. A four-year observation program starting in 2015 includes four regions of the sky of the above size every year, with the discovered exoplanets being further investigated with the various instruments of the observatory's unit telescopes.

The four domes of the SPECULOOS telescopes next to the NGTS. In the background the VISTA (right) and the Paranal summit.


The SPECULOOS SSO ( S earch for habitable P lanets EC lipsing UL tra-c OO l S tars S outhern O bservatory ) is an ensemble of 4 reflector telescopes belonging to the SPECULOOS research project in order to be able to work together with a similar one (as of the end of 2018 ) Ensemble in the northern hemisphere ( Teide , Tenerife ) to discover earth-like exoplanets in the vicinity of cool stars of the spectral class M7 up to brown dwarfs ; it builds on the experience with TRAPPIST . Scientific operations will begin in January 2019. The telescopes are remote-controlled, follow the Ritchey-Chrétien design with a primary mirror 1 meter in diameter, and have cameras with high sensitivity in the near infrared. The telescopes were named after four large moons of Jupiter : Io , Europa , Ganymede and Callisto .

Observe at the Paranal Observatory

Observation time can be requested twice a year for the semester after next . Depending on the telescope, two to five times as much time is requested as can actually be allocated. The proposals are weighted by an advisory body according to scientific quality and urgency. After the approval, the astronomer defines the detailed sequence of the observations in so-called " Observing Blocks " (OBs) at home . Either only these OBs, together with the desired observation conditions, are sent to Paranal for execution, for service mode observation, or the astronomer himself travels to Chile for visitor mode observation.

Course of the observations

The telescopes on the Paranal plateau opened for the night ahead

At the telescope there is always an engineer, the “ Telescope and Instrument Operator ” (TIO), and an astronomer, the “ Nighttime Astronomer ” (NA) of ESO. In service mode, the NA decides on the basis of the observation conditions which OBs can be executed with a chance of success and carries out the observations together with the TIO, which is responsible for the telescope and the technical process. After the data has been saved, the NA decides whether it meets the requirements of the applicant or whether the OB needs to be repeated. For the astronomers who mostly come from ESO member countries and who work on Paranal, on the other hand, it is not their own scientific work that determines everyday work, but rather the unwinding of "service programs".

Control room of the observatory in the control building

In visitor mode, the visitor has the task of making critical decisions about the OBs that could not be estimated in advance, for example when objects that are subject to change are to be observed. As a disadvantage, however, the visitor has no influence on the weather conditions under which his program is carried out, since the observation dates for the visitor mode are set around six months in advance.

During the day, a “ daytime astronomer ” typically looks after two telescopes. He carries out calibrations for last night's observations, takes care of solving any problems that may have occurred during the night and prepares the telescope for the next night.

Monitoring the observation conditions

The DIMM telescope is located on a tower in order not to be affected by air turbulence close to the ground.

In order to not only have subjective impressions of the observation conditions by the engineers and astronomers working at the telescopes, a system for “ Astronomical Site Monitoring ” was set up, which automatically records and archives the data. In addition to numerous sensors for measuring meteorological conditions such as air and soil temperature, humidity, wind speed and direction as well as dust particle density, special astronomical parameters are also measured. “ Seeing ” is measured by a small 35 cm special telescope, the DIMM, which measures the image quality approximately every two minutes throughout the night. Instead of taking a simple picture and measuring the size of the star shown, it compares the wavefront of two sub-apertures about 20 cm apart, each 4 cm in diameter. This has the advantage of measuring other properties of the current turbulence in the atmosphere, which are of particular interest for interferometry, in addition to seeing. The transparency of the atmosphere is measured using the same image, except that instead of the image size, the incoming flow of the star is measured and compared with table values ​​for a clear atmosphere.

A second instrument that MASCOT ( M ini A ll S ky C loud O bservation T ool ), undergoes a fish eye lens images of the entire sky, and allows an estimate of the cloud cover. In addition, ESO processes the current satellite data in order to provide the observers at the telescopes with information about the expected observation conditions.

Scientific results

From the beginning of the scientific operation of the VLT on April 1, 1999 , up to 2005, over 1000 articles were published in recognized specialist journals based on data from the Paranal Observatory. The main results include:

  • The first direct images of an exoplanet were made with the VLT. It is not entirely certain whether this honor goes to GQ Lupi b or the planet 2M1207b , but both images are from NACO.
  • The deep impact mission was observed from all ESO telescopes. In addition to images, spectrography also provided new results on the chemical composition of the comet Tempel 1 .
  • With ISAAC, the distance to the galaxy NGC 300 could be determined more precisely than to any other galaxy outside the immediate vicinity of the Milky Way. Such distance determinations with the help of the Cepheids form an important basis for cosmic distance measurements.
  • The faint companion of the AB Doradus was mapped directly for the first time with NACO-SDI, whereby its mass could be determined with the help of Kepler's laws . This brown dwarf is twice as heavy as theoretically expected, which presumably requires changes to the theory of the internal structure of stars and the abundance of planets and brown dwarfs.
  • By chance, a bright meteor crossed the FORS 1's field of view when spectra were being recorded. It is the first precisely calibrated spectrum of such a luminous phenomenon.
  • FORS 2 and ISAAC jointly hold the record for the most distant gamma-ray flash at z = 6.3.
  • With the VLTI, not only the diameter but also the shape of the stars can be determined. While Eta Carinae with its strong stellar wind seems drawn to the poles in the length, is Achernar by its rapid rotation to the limit of the theoretically possible flattened .
  • For the first time, the VLTI was used to interferometrically resolve an extragalactic object in the mid- infrared range at 10 μm, the active core of the galaxy NGC 1068 . This Seyfert galaxy is home to a black hole of around 100 million solar masses .
  • Using a occultation by Pluto moon Charon on 11 July 2005 with the VLT its exact diameter determined to 1,207.2 km for the first time. The temperature could also be measured at −230 ° C, which is about 10 K colder than previously assumed.
  • With the help of the new NACO SDI (NACO Simultaneous Differential Imager) at the VLT, a brown dwarf and a companion were discovered at the beginning of 2006 , which are only 12.7 light years away from Earth.
  • Through observations of the brown dwarf 2MASS1207-3932 with the VLT it was discovered in May 2007 that the object not only has an orbiting planet, which was the first exoplanet to be observed directly, but also, like young stars, is surrounded by a disk of gas and dust is. In addition, astronomers were able to prove that the brown dwarf also has a jet .
  • With the VLTI it was possible to resolve the star Theta 1 Ori C in the trapezoid , i.e. the central area of ​​the Orion Nebula , as a double star and to track the orbit between January 2007 and March 2008. Various interconnections of three telescopes with a base length of 130 m with VLTI / AMBER in the near infrared (H- and K-band, 1.6 and 2.2 μm) achieved a resolution of 2  mas .

See also


Issue 92, June 1998: VLT First Light (PDF; 1.1 MB)
Issue 93, September 1998: VLT Science Verification (PDF; 1.6 MB)
Issue 104, June 2001: VLTI First Fringes (PDF; 2.9 MB)
Issue 120, June 2005: The VLT Survey Telescope (PDF; 8.1 MB)

Web links

Commons : Paranal Observatory  - collection of images, videos and audio files

Individual evidence

  1. EVALSO: A New High-speed Data Link to Chilean Observatories 4 November 2010
  2. ESO Press Release 19/99: REOSC Delivers the Best Astronomical Mirror in the World to ESO (December 14, 1999) (Retrieved April 17, 2012)
  3. First Light for YEPUN
  4. ESO - The Very Large Telescope ( Memento of the original from May 27, 2005 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot /
  5. ESO - The Very Large Telescope ( Memento of the original from May 27, 2005 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice.  @1@ 2Template: Webachiv / IABot /
  6. The world's most powerful laser guide star system sees the first light at the Paranal observatory
  7. a b c Paranal News . From:, accessed July 16, 2010
  10. First light for the exoplanet camera SPHERE, accessed on June 5, 2014
  12. ( Memento of the original from October 17, 2010 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot /
  13. PIONIER website
  14. ESO Press Release 1148: Vampire Star Reveals its Secrets (December 7, 2011)
  16. GRAVITY ,
  17. MATISSE ,
  18. The MATISSE instrument sees its first light on ESO's Very Large Telescope Interferometer., March 5, 2018
  19. First Light of the VST
  20. VISTA - Visible and Infrared Survey Telescope for Astronomy
  21. a b c New telescopes for hunting exoplanets on the Paranal
  22. ASA Astrograph H f 2.8
  23. SPECULOOS. University of Liège , accessed December 30, 2018 (French).
  24. L'Observatoire SPECULOOS North. University of Liège, accessed December 30, 2018 (French).
  25. First Light for SPECULOOS. European Southern Observatory , December 5, 2018, accessed December 30, 2018 .
  26. Peter Prantner: "Galileo would have loved it". Europe's flagship astronomy in Chile. In: November 29, 2012, accessed April 3, 2013 .
  27. ESO Press Release 23/04: Is This Speck of Light an Exoplanet? (September 10, 2004)
  28. a b ESO Press Release 12/05: Yes, it is the Image of an Exoplanet (April 30, 2005)
  29. ESO Press Release 09/05: Is this a Brown Dwarf or an Exoplanet? (April 7, 2005)
  30. ESO Press Release 19/05: Comet Tempel 1 Went Back to Sleep (July 14, 2005)
  31. ESO Press Release 15/05: Preparing for the Impact (May 30, 2005)
  32. ESO Press Release 20/05: Moving Closer to the Grand Spiral (August 1, 2005)
  33. ESO Press Release 19/04: Catching a Falling Star (July 30, 2004)
  34. ESO Press Release 22/05: Star Death Beacon at the Edge of the Universe (September 12, 2005)
  35. ESO Press Release 31/03: Biggest Star in Our Galaxy Sits within a Rugby-Ball Shaped Cocoon (November 18, 2003)
  36. ESO Press Release 14/03: Flattest Star Ever Seen (June 11, 2003)
  37. ESO Press Release 17/03: A First Look at the Donut Around a Giant Black Hole (June 19, 2003)
  38. ESO 02/06 - Science Release: Measuring the Size of a Small, Frost World (January 4, 2006)
  39. ESO 11/06 - Science release: The Sun's New Exotic Neighbor (March 22, 2006)
  40. Stefan Deiters: Brown dwarfs - the smallest object with a jet. Retrieved May 24, 2007 .
  41. Stefan Kraus et al .: Tracing the young massive high-eccentricity binary system θ 1 Orionis C through periastron passage . (PDF) In: Astronomy & Astrophysics . 497, Jan 2009, pp. 195-207. doi : 10.1051 / 0004-6361 / 200810368 . Retrieved April 4, 2009.

Coordinates: 24 ° 37 ′ 38 ″  S , 70 ° 24 ′ 15 ″  W

This article was added to the list of excellent articles on March 27, 2006 in this version .