Picture of the Week

7 February 2011

HAWK-I Instrument Spies a Super Galaxy

The HAWK-I instrument on ESO's Very Large Telescope (VLT) at the Paranal Observatory in Chile has been used to great effect in producing this distinctive image of the distant galaxy NGC 157. Boasting a central sweep of stars resembling a giant "S", reminiscent of the comic book hero Superman’s symbol, this celestial spiral is indeed a super example of how new technology is helping us to learn more about the cosmos.

HAWK-I stands for High-Acuity Wide-field K-band Imager, and it is one of the latest and most powerful instruments on the VLT. It detects infrared light, allowing us to peer through the gas and dust that normally obscures our view. This reveals an otherwise hidden view of the Universe, and gives astronomers the opportunity to study dense areas of star formation.

Learning more about star formation is an important step towards expanding our understanding of our own origins. The same processes that are coalescing material in NGC 157 and creating stars there took place around 4.5 billion years ago in the Milky Way to form our own star, the Sun.

NGC 157 is faint at about magnitude 11, but can be tracked down by dedicated amateur astronomers. It is located within the constellation of Cetus (the Sea Monster).

31 January 2011

From One "Alien World" to Another

What looks like a barren and inhospitable alien landscape in this 360-degree panorama is in fact the site for ESO’s European Extremely Large Telescope, or E-ELT for short. When construction begins the uninhabited mountaintop left of the centre will become a hive of activity as engineers, technicians and scientists work on building the world’s biggest eye on the sky.

In many ways Chile’s Cerro Armazones may seem like an alien world. The environment is harsh, with low humidity and air pressure, a blazing Sun during the day, but breathtaking skies at night. Cerro Armazones is in the Atacama Desert — one of the driest places on Earth. These conditions, combined with its remoteness, are what make the region such an excellent location for telescopes. Armazones is an isolated peak, 3060 metres above sea level. It is about 20 km away from Cerro Paranal, home of ESO's famous Very Large Telescope. Both summits enjoy crisp skies far away from sources of light pollution.

Among the ELT’s many science goals is a particularly hot topic in contemporary astronomy: the quest for exoplanets. The E-ELT will search for Earth-like planets orbiting other stars and could even directly image larger planets or probe their atmospheres. The E-ELT’s high-tech instruments will also study the formation of planets in protoplanetary discs around young stars. Detecting water and organic molecules will shed light on how planetary systems are produced, and could bring us one step closer to answering the question of whether we are alone in the Universe.

This panorama was taken by ESO Photo Ambassador Serge Brunier.


24 January 2011

A New Era for Astronomy

As the Sun sets over Cerro Armazones, plans are well advanced for building the world's biggest “eye on the sky”: ESO's European Extremely Large Telescope (E-ELT). With a primary mirror 39 metres in diameter, the E-ELT will dwarf all existing visible-light telescopes.

Site selection has been a vital part of the plans for the E-ELT. Over the course of several years a team of experts investigated locations around the world, looking for the best place to host such an ambitious project. The site for the E-ELT must be remote enough not to be influenced by problems such as light pollution, but also needs the necessary infrastructure for the construction and operation of the observatory, and to accommodate the over 150 staff who will eventually work there. Monitoring stations, such as the one shown here, were set up to test site conditions scientifically by measuring parameters that included atmospheric turbulence and levels of water vapour. By better understanding the atmosphere at a site, the team were able to determine the best potential site for the highest quality science.

The list of potential sites included areas in Argentina, in Chile, in Morocco and in Spain. Cerro Armazones in Chile, shown in this photograph, was finally selected as the E-ELT site because it has the best balance of sky quality across all aspects and it can be operated in an integrated fashion with the existing ESO Paranal Observatory nearby. Armazones is about 20 km from Paranal and 130 km south of the nearest town. It is 3060 metres above sea level and boasts almost 350 cloudless nights a year.

Constructing the E-ELT is a huge undertaking that will take several years. The go-ahead for construction is planned for 2011, with start of operations planned for early in the next decade. When observations begin, the E-ELT will herald a new era for astronomy.

17 January 2011

Sailing the Atacama Desert

Like the bow of a ship sailing a rolling ocean of red hills, the southeast corner of the observing platform at Paranal stands over the Mars-like landscape of the Chilean Atacama Desert. This panorama shows the breathtaking view of the horizon, and conveys the feeling of immensity experienced when looking from the top of Cerro Paranal, a remote 2600-metre-high mountain located in one of the driest regions on Earth.

Atop Cerro Paranal is the ESO Very Large Telescope (VLT), the world’s most advanced optical and near infrared ground-based astronomical facility, composed of four 8.2-metre Unit Telescopes (UTs) and four 1.8-metre Auxiliary Telescopes (ATs). The fourth Unit Telescope (UT4), named Yepun in the Mapuche language, is most prominent in this photograph, while UT3 (Melipal) and UT1 (Antu) are just visible on the right-hand edge of the picture. Three of the smaller ATs can also be seen on the 200-metre-wide observing platform. The yellow structure in front of Yepun is the “M1 Lifting Platform”, used to move the 8.2-metre-diameter primary mirror (M1) and its support structure out of the telescope building for periodic recoating.

In the distance, over the edge of the platform, is the Paranal Observatory base camp, which includes the Residencia, the Main Maintenance Building, the power station and the warehouse. These facilities are situated some 2 km away from the telescopes, at a lower altitude of about 2400 metres. The whole observatory complex operates as an “island” in the desert, where essentials such as water, food and fuel must be brought from Antofagasta, located about 120 km to the north. The remoteness of the site makes operating Paranal Observatory a great logistical challenge, but the reward is a location with superb conditions for astronomy.

10 January 2011

The VLT “Venus” and the Belt of Venus

Before another clear, starry night falls at ESO's Paranal Observatory, home of the Very Large Telescope (VLT), the sky produces a palette of intense colours, putting on a beautiful show for observers. These colours can only be seen with such depth from sites such as Paranal, where the atmosphere is extraordinarily pure. Looking to the west, over the Pacific Ocean, the sunset sky turns bright orange and red. However, this photograph shows the view to the east instead, looking away from the Sun after it has just set. The grey-bluish shadow above the horizon is the shadow of our own planet. Above this is a pinkish glow known as the "Belt of Venus", a phenomenon produced by the reddened light of the setting Sun being backscattered by the Earth's atmosphere.

In the centre of the image is the fourth 8.2-metre Unit Telescope (UT4), part of the VLT. The Mapuche name given to UT4 is Yepun, which means Venus. As well as working as individual telescopes, groups of two or three UTs can combine their light using a technique called interferometry, which allows astronomers to see details up to 25 times finer than with the individual telescopes. The VLT also has four 1.8-metre Auxiliary Telescopes (ATs), housed in ultra-compact mobile enclosures, which are fully dedicated to interferometric observations. Two of the ATs are visible in the background, with a third mostly hidden.

The yellow frame-like structure in front of Yepun is the "M1 Lifting Platform", used when the giant 8.2-metre primary mirror (M1) of the telescope is periodically recoated. The delicate mirror and its support structure, which together weigh 45 tonnes, are removed from the telescope enclosure and slowly driven about two kilometres to a maintenance building at the Paranal base camp. This process is, unsurprisingly, performed with the utmost care.


3 January 2011

Another Perfect Day at Paranal

Rolling red hills stretch out below the exceptionally clear blue sky that is typical of ESO's Paranal Observatory. Although the telescope domes close at dawn, and nothing seems to move on the surface of this barren desert, the ESO Very Large Telescope (VLT) never rests. Since early morning, a team of engineers and technicians has been working hard to prepare the telescopes and instruments for another "perfect night".

The 2600-metre-high Cerro Paranal stands out at the centre of this panoramic view, taken looking towards the south. This flattened mountaintop is home to the VLT, the world's most advanced ground-based optical and near infrared astronomical facility. The VLT has four 8.2-metre Unit Telescopes (UTs), plus four 1.8-metre Auxiliary Telescopes (ATs). In this picture, only two of the UT enclosures, together with the smaller 2.6-metre VLT Survey Telescope (VST) are visible.

To the right of Cerro Paranal, the sea of clouds that typically covers the coast of the Pacific Ocean — only 12 km away — is visible in the background. The cold oceanic stream typically keeps the thermal inversion layer of the atmosphere below an altitude of 1500 metres, making this remote area of the Chilean Atacama Desert in the II Region of Chile one of the driest sites on Earth and a perfect window on the Universe. The atmosphere here is extremely dry and clear, and has very low turbulence, offering the most suitable conditions for optical and near-infrared astronomical observations.

For this reason, the 3060-metre-high Cerro Armazones, located just some 20 km east of Paranal, was selected as the site for the future European Extremely Large Telescope (E-ELT). With a primary mirror 39 metres in diameter, the E-ELT will be the world's largest eye on the sky.

This photograph was taken from a neighbouring mountain, home of the 4.1-metre Visible and Infrared Survey Telescope for Astronomy (VISTA). VISTA started operations at the end of 2009 and is the most recent telescope to be added to the roster at ESO's Paranal Observatory. VISTA is the largest survey telescope in the world.




27 December 2010

The Long and Winding Road*

This splendid picture shows the European Southern Observatory's Very Large Telescope (VLT) on Cerro Paranal in the Chilean Atacama desert. The mountaintop, 120 km south of the town of Antofagasta, is a remote haven for scientific exploration.

Its distance from populated areas means that light pollution is essentially non-existent, which helps to guarantee clear views for the telescopes. It also ensures that activity is not disturbed by other human activities, such as traffic on nearby roads or dusty air from mines. The desert location means that moisture in the atmosphere is at a very low level, which contributes to the excellent atmospheric conditions. As well as the VLT, Paranal Observatory is also home to the VISTA telescope on an adjacent peak, from which this photograph was taken. The road which links the two peaks can be seen in the centre of the image, winding through the desert landscape.

The two distinct bright patches seen here in the night sky are the Large and Small Magellanic clouds, which are neighbouring galaxies to the Milky Way, about 160 000 and 200 000 light-years away respectively. The path of the Milky Way itself can be seen on the left of the image. Astronomers use the VLT to study our own galaxy, the neighbouring Magellanic Clouds, and naturally also much more distant galaxies billions of light-years from Earth. On the long and winding road to the stars, observatories like the VLT are our first steps.


20 December 2010

Monuments of Science*

On a remote mountaintop, 2600 metres above sea level in the Chilean Atacama Desert, lies the world’s most advanced visible-light observatory. The European Southern Observatory’s Very Large Telescope (VLT) is not only a window on the Universe; it is also a celebration of modern science and technology.

This photograph shows two of the four Unit Telescopes that make up the VLT. With its giant 8.2-metre diameter mirrors, sensitive detectors, and state-of-the art adaptive optics system, the VLT uses cutting-edge technology at every opportunity. Even the telescope enclosures — the domes — are highly advanced, being thermally controlled to reduce air turbulence in the telescope structure.

Every night the VLT studies the sky to make discoveries about the Universe. Visible in this photo, sweeping between the two Unit Telescopes, is the plane of the Milky Way. Containing billions of stars, it is our own corner of the cosmos, but the VLT's vision can peer much deeper than this, our home galaxy, and look out to the extremes of space, all in the name of science and discovery.

This image is available as a mounted image in the ESOshop.


13 December 2010

Collecting Precious Starlight*

As soon as the Sun sets over the Chilean Atacama Desert, ESO’s Very Large Telescope (VLT) begins catching light from the far reaches of the Universe. The VLT has four 8.2-metre Unit Telescopes such as the one shown in the photograph. Many of the photons — particles of light — that are collected have travelled through space for billions of years before reaching the telescope’s primary mirror. The giant mirror acts like a high-tech “light bucket”, gathering as many photons as possible and sending them to sensitive detectors. Careful analysis of the data from these instruments allows astronomers to unravel the mysteries of the cosmos.

The telescopes have a variety of instruments, which allow them to observe in a range of wavelengths from near-ultraviolet to mid-infrared. The VLT also boasts advanced adaptive optics systems, which counteract the blurring effects of the Earth's atmosphere, producing images so sharp that they could almost have been taken in space.


This image is available as a mounted image in the ESOshop.

6 December 2010

Up Close and Personal with the Very Large Telescope

Imagine being a fly on the wall of ESO's Very Large Telescope (VLT) at the world's most advanced optical observatory. You could have a view a little like this. Fish-eye photography gives this unusual view of the 8.2-metre diameter telescope, poised and ready to begin gathering light from the deep recesses of the Universe as soon as the dome opens and starlight pours in.

The VLT has four of these 8.2-metre Unit Telescopes, called Antu, Kueyen, Melipal and Yepun. These are the Mapuche names for the Sun, Moon, Southern Cross and Venus. This photograph shows Yepun. The names are from the native language of the indigenous people who live mostly in the area south of the Bio-Bio River, some 500 km south of Santiago de Chile.

The VLT is so powerful that it allows us to see objects four thousand million times fainter than those that can be seen with the unaided eye. This has helped make ESO the most productive ground-based observatory in the world.


29 November 2010

Crash of the Titans

NGC 520 — also known as Arp 157 — looks like a galaxy in the midst of exploding. In reality, it’s the exact opposite. Two enormous spiral galaxies are crashing into each other, melding and forming a new conglomerate. This happens slowly, over millions of years — the whole process started some 300 million years ago. The object, about 100 000 light-years across, is now in the middle stage of the merging process, as the two nuclei haven’t merged yet, but the two discs have. The merger features a tail of stars and a prominent dust lane. NGC 520 is one of the brightest interacting galaxies in the sky and lies in the direction of Pisces (the Fish), approximately 100 million light-years from Earth.

This image was taken by the ESO Faint Object Spectrograph and Camera attached to the 3.6-metre telescope at La Silla in Chile. It is based on data obtained through B, V, R and H-alpha filters.

22 November 2010

Looking into the Milky Way’s Heart — ISAAC observes the Galactic Centre

The centre of our own galaxy, the Milky Way, is again in the sights of ESO telescopes. This time it’s the turn of ISAAC, the VLT’s near- and mid-infrared spectrometer and camera.

From Chile’s Atacama Desert, site of the ESO observatories, the Milky Way offers magnificent views, particularly in the southern hemisphere winter, when the central region of our galaxy is most visible (see eso0934). However, the Galactic Centre itself, located about  27 000 light-years away in the constellation of Sagittarius, hides behind thick clouds of interstellar dust, which appear as dark obscuring lanes in visible light, but which are transparent at longer wavelengths such as the infrared. In this image, the infrared observations clearly reveal the dense clustering of stars in the galactic core.

ESO telescopes have been tracking stars orbiting the centre of the Milky Way for more than 18 years, getting the highest resolution images of this area and providing a definitive proof of the existence of a supermassive black hole in the heart of our galaxy (read more in eso0226 and eso0846). Infrared flashes emitted by hot gas falling into the supermassive black hole have also been detected with ESO telescopes (see eso0330).

This representative-colour picture is composed of images taken by ISAAC at near-infrared wavelengths through 2.25, 2.09, and 1.71 µm narrowband filters (shown in red, green and blue respectively). It covers a field of view of 2.5 arcminutes.

15 November 2010

An Ancient Cluster of Stars Against a Stunning Background

Among the myriad of stars in this image shines NGC 2257, a collection of cosmic gems bound tightly by gravity. Many billions of years old, but still sparkling brightly, it is an eye-catching astronomical object.

NGC 2257 is a globular cluster, the name given to the roughly spherical concentrations of stars that orbit galactic cores, but are often found far out from the centres in the halo areas of galaxies. Globular clusters contain very old stars, being typically over 10 billion years old, and can therefore be used like a "fossil record" to learn more about the Universe’s past. They are densely packed, with tens to hundreds of thousands of stars gathered within a diameter of just a few tens of light-years. NGC 2257 lies on the outskirts of the Large Magellanic Cloud (LMC), a satellite galaxy of our own Milky Way. It is one of 15 very old globular clusters in the LMC.

The image is made from data taken with the Wide Field Imager instrument on the 2.2-metre MPG/ESO telescope at La Silla, in B, V and I filters, which are shown here in blue, green and red respectively. The field of view is approximately 20 by 20 arcminutes. These observations were made as part of the ESO Imaging Survey project, which was planned to make public imaging surveys to identify targets for follow-up observations with the Very Large Telescope.


8 November 2010

Shooting a Laser at the Galactic Centre

This impressive image, taken on 10 May 2010 by ESO astronomer Yuri Beletsky, beautifully depicts the sky above Paranal. One of the 8.2-metre telescopes of ESO's Very Large Telescope, Yepun, Unit Telescope 4, is seen against the wonderful backdrop of the myriad of stars and dust that makes up the Milky Way. A laser beam is coming out of Yepun, aiming perfectly at the Galactic Centre. When used with the adaptive optics system the artificial star created by the beam allows the telescope to obtain images and spectra that are free from the blurring effect of the atmosphere. When this image was taken, astronomers Stefan Gillessen and Hauke Enkel were using the SINFONI instrument, together with the laser guide star facility, to study the centre of our Milky Way, where a supermassive black hole is lurking.

The field of view of the image is very wide, about 180 degrees. One of the 1.8-metre Auxiliary Telescopes used for interferometry can be seen on the right.

1 November 2010

ESO’s Very Large Telescope Peers into a Distant Nebula*

Astronomers using data from ESO's Very Large Telescope (VLT), at the Paranal Observatory in Chile, have made an impressive composite of the nebula Messier 17, also known as the Omega Nebula or the Swan Nebula. The painting-like image shows vast clouds of gas and dust illuminated by the intense radiation from young stars.

The image shows a central region about 15 light-years across, although the entire nebula is even larger, about 40 light-years in total. Messier 17 is in the constellation of Sagittarius (the Archer), about 6000 light-years from Earth. It is a popular target for amateur astronomers, who can obtain good quality images using small telescopes.

These deep VLT observations were made at near-infrared wavelengths with the ISAAC instrument. The filters used were J (1.25 µm, shown in blue), H (1.6 µm, shown in green), and K (2.2 µm, shown in red). In the centre of the image is a cluster of massive young stars whose intense radiation makes the surrounding hydrogen gas glow. To the lower right of the cluster is a huge cloud of molecular gas. At visible wavelengths, dust grains in the cloud obscure our view, but by observing in infrared light, the glow of the hydrogen gas behind the cloud can be seen shining faintly through. Hidden in this region, which has a dark reddish appearance, the astronomers found the opaque silhouette of a disc of gas and dust. Although it is small in this image, the disc has a diameter of about 20 000 AU, dwarfing our Solar System (1 AU is the distance between the Earth and the Sun). It is thought that this disc is rotating and feeding material onto a central protostar — an early stage in the formation of a new star.

This image is available as a mounted image in the ESOshop.


  • The research for which these observations were originally made was described in ESO press release eso0416.

25 October 2010

Starry La Silla

The stars rotate around the southern celestial pole during a night at ESO’s La Silla Observatory in northern Chile. The fuzzy parts in the trails on the right are due to the Magellanic Clouds, two small galaxies neighbouring the Milky Way. The dome seen in the image hosts ESO’s 3.6-metre telescope and is home to HARPS (High Accuracy Radial velocity Planet Searcher), the world’s foremost exoplanet hunter. The rectangular building seen in the lower right of the image contains the 0.25-metre TAROT telescope, designed to react very quickly when a gamma-ray burst is detected. Other telescopes at La Silla include the 2.2-metre MPG/ESO telescope, and the 3.58-metre New Technology Telescope, the first telescope to use active optics and, as such, the precursor to all modern large telescopes. La Silla was ESO’s first observing site and is still one of the premier observatories in the southern hemisphere.


18 October 2010

Reflecting on the VLT

The Sun sets at ESO’s Very Large Telescope (VLT) in this image. Taken at the observatory on Cerro Paranal in the dry Atacama Desert of Chile, the observatory’s four 8.2-metre telescopes can be seen preparing for the night ahead. Three of the VLT’s four Auxiliary 1.8-metre Telescopes (AT), used for interferometry, are also visible. The telescopes are seen reflected in the protection cover of one of the AT stations. The ATs are mounted on tracks and can be moved between precisely defined observing positions from where the beams of collected light are combined in the interferometric laboratory. The ATs are very unusual telescopes, as they are self-contained in their own ultra-compact protective domes, and travel with their own electronics, ventilation, hydraulics and cooling systems. Each AT has a transporter that lifts the telescope and moves it from one position to the other. At 2600 metres above sea level, the observing climate is excellent, with little disturbance from clouds. 

11 October 2010

New Temporary Offices at ESO Headquarters

ESO has grown significantly since 1980, when its European staff originally moved from offices at CERN to a dedicated headquarters building in Garching, near Munich, Germany. In the intervening three decades the number of ESO’s member states has increased from six to fourteen, and the organisation has achieved milestones such as the First Light of the New Technology Telescope at La Silla and of the Very Large Telescope at Paranal, becoming in the process the most productive observatory in the world. Today, ESO is constructing the Atacama Large Millimeter/submillimeter Array at Chajnantor in collaboration with international partners, and is in the detailed design phase of a 40-metre-class European Extremely Large Telescope, which will be “the world’s biggest eye on the sky”.

Over the years, the number of ESO staff working in Garching has increased from about 100 to about 450, as the organisation has grown and tackled these exciting new projects. When the capacity of the headquarters building was exceeded, it became necessary to rent additional office space elsewhere on the Garching Forschungszentrum research campus. A recent development during the summer of 2010 is the construction of several new temporary office buildings, seen on the left in this photograph, which are immediately adjacent to the main headquarters (on the right). These buildings make it possible to bring more of the ESO Garching staff onto the main headquarters site from their scattered offices around the campus, so that people can work more easily together. It is planned that a new permanent building, next to the original headquarters, will be constructed for offices and meeting facilities.

4 October 2010

ALMA Antennas on Chajnantor

Two of the Atacama Large Millimeter/submillimeter Array (ALMA) 12-metre antennas gaze at the sky at the observatory’s Array Operations Site (AOS), high on the Chajnantor plateau at an altitude of 5000 metres in the Chilean Andes.

Eight antennas have been installed at the AOS since November 2009. More antennas will be installed on the Chajnantor plateau during the next months and beyond, allowing astronomers to start producing early scientific results with the ALMA system around late 2011. After this, the interferometer will steadily grow to reach its full scientific potential, with at least 66 antennas.

ALMA is the largest ground-based astronomy project in existence, and will comprise a giant array of 12-metre submillimetre quality antennas, with baselines of up to about 16 kilometres. An additional, compact array of 7-metre and 12-metre antennas will complement the main array. The ALMA project is an international collaboration between Europe, East Asia and North America in cooperation with the Republic of Chile. ESO is the European partner in ALMA.

27 September 2010

A Solargraph taken from APEX at Chajnantor

This unusual and artistic image, made using a technique known as "solargraphy" in which a pinhole camera captures the movement of the Sun in the sky over many months, was taken from the Atacama Pathfinder Experiment (APEX) telescope on the plateau of Chajnantor. The plateau is also where ESO, together with international partners, is building the Atacama Large Millimeter/submillimeter Array (ALMA). The solar trails in the image were recorded over half a year and clearly show the quality of the 5000-metre altitude site, high in the Chilean Andes, for astronomical observations.

The idea for creating the solargraphs at ESO's telescopes came from Bob Fosbury, an astronomer based at ESO Headquarters in Germany, after learning about the technique from Finnish artist Tarja Trygg. Trygg provided the cameras, known as "cans". The cans are constructed from small black plastic canisters used for storing 35 mm film cassettes. A pinhole in a sheet of aluminium foil is placed over a small aperture drilled into the side of the can, and a rectangle of black and white photographic printing paper is curled and placed snugly around the inside of the can.

Two cans were sent to APEX where David Rabanus, the APEX Station Manager, mounted one facing west of north on the gatepost of the telescope enclosure, close to the telescope itself, and the other on the roof of the generator powerhouse facing east of north. Both were pointed at an elevation of about 45 degrees. The cans at APEX were exposed for a full six months from mid-December 2009 until the southern winter solstice in June 2010. The image from the second can is shown here. It includes the tilted profile of Cerro Chajnantor on the right, silhouetted against the trails of the rising Sun. The mostly unbroken solar trails show that there were some clouds at the ALMA site during the six months — but not many! This solargraph is so sharp that holes in the fleeting clouds over Chajnantor on the few partly cloudy days sometimes managed to create individual "snapshots" of the solar disc (seen as dots in the broken sequences).

The colours appearing in this pinhole camera picture are not related to the actual colours of the scene. The colour comes from the appearance of finely divided metallic silver growing on silver halide grains. With solargraphic images, the photographic paper is not developed but simply scanned with a normal colour scanner after exposure and then "inverted" — switched from negative to positive — in the computer. This reveals the latent image, which in a normal photograph consists of around ten silver atoms per billion atoms of silver halide grain and is usually invisible. On continued exposure however, the latent image clumps grow so that the first visible signs of an image are yellowish, which then darkens to sepia and finally to a maroonish-brown hue as the particle size increases. Eventually the maximum exposure produces a slate-grey shade.

APEX is a collaboration between the Max-Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO. The telescope is operated by ESO.


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