Picture of the Week 2011

26 December 2011

Inside Euler's Head — Or how to see a telescope through the walls of its dome

As night was falling over ESO’s La Silla Observatory in Chile on 20 December 2009, the sky was not yet dark enough for the telescopes to start observations. But conditions were perfect to perform a clever trick with the dome of the Swiss 1.2-metre Leonhard Euler Telescope: allowing us to peer inside with this photograph apparently taken through the dome.

This image is a 75-second exposure taken while the slit of the Euler telescope’s dome was performing half a rotation at full speed. Through the ghostly blur of the moving dome walls, the telescope is clearly visible. A dim light was switched on in the interior of the building especially for the purpose of this photo.

The picture was taken by Malte Tewes, a young astronomer from the École Polytechnique Fédérale de Lausanne in Switzerland, who had just finished a two-week observing run at the telescope on the evening in question. The next observer, Amaury Triaud, and the telescope’s technician, Vincent Mégevand (both pictured), were on site so they could operate the dome from the inside while Malte took the photograph from outside.

The road that leads to ESO’s nearby 3.6-metre telescope is visible lined by a chain of lights to the left of the image. In addition to the 3.6-metre telescope, the New Technology Telescope, and the MPG/ESO 2.2-metre telescope, La Silla Observatory also hosts several national and project telescopes that are not operated by ESO. The Euler telescope, named after the famous Swiss mathematician Leonhard Euler, is one of them.


19 December 2011

Llullaillaco, Clear as Day

Bathed in the pristine light of the Chilean Atacama Desert, the ESO VLT’s Auxiliary Telescope 2 stands on Cerro Paranal. It is one of four that are used with the Very Large Telescope Interferometer. During the day, its bulbous dome is closed, protecting the sensitive telescope within.

The magnificent 6739-metre volcano Llullaillaco stands proudly in the background of this photograph. Although it looks relatively close on the horizon, it is actually an incredible 190 kilometres away, on the border with Argentina. That Llullaillaco can be seen so clearly is evidence of the region’s unparallelled atmospheric conditions. The clear air is one of the many factors that make this such a wonderful location for astronomical observatories. It is from this excellent vantage point that ESO astronomers study objects that are not just hundreds of kilometres in the distance, but billions of light-years away.

This photograph was taken by ESO Photo Ambassador Gianluca Lombardi.


12 December 2011

ALMA's World At Night

This panoramic view of the Chajnantor plateau, spanning about 180 degrees from north (on the left) to south (on the right) shows the antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) ranged across the unearthly landscape. Some familiar celestial objects can be seen in the night sky behind them. These crystal-clear night skies explain why Chile is the home of not only ALMA, but also several other astronomical observatories. This image is just part of an even wider panorama of Chajnantor.

In the foreground, the 12-metre diameter ALMA antennas are in action, working as one giant telescope, during the observatory’s first phase of scientific observations. On the far left, a cluster of smaller 7-metre antennas for ALMA’s compact array can be seen illuminated. The crescent Moon, although not visible in this image, casts stark shadows over all the antennas.

In the sky above the antennas, the most prominent bright “star” — on the left of the image — is in fact the planet Jupiter. The gas giant is the third brightest natural object in the night sky, after the Moon and Venus. The Large and Small Magellanic Clouds can also be clearly seen on the right of the image. The Large Magellanic Cloud looks like a puff of smoke, just above the rightmost antenna. The Small Magellanic Cloud is higher in the sky, towards the upper-right corner. Both “clouds” are in fact dwarf irregular galaxies, orbiting the Milky Way galaxy, at distances of about 160 000 and 200 000 light-years respectively.

On the far left of the panorama, just left of the foreground antennas, is the elongated smudge of the Andromeda galaxy. This galaxy, more than ten times further away than the Magellanic Clouds, is our closest major neighbouring galaxy. It is also the largest galaxy in the Local Group — the group of about 30 galaxies which includes our own — and contains approximately one trillion stars, more than twice as many as the Milky Way. It is the only major galaxy visible with the naked eye. Even though only its most central region is apparent in this image, the galaxy spans the equivalent of six full Moons in the sky.

This photograph was taken by Babak Tafreshi, the latest ESO Photo Ambassador. Babak is also founder of The World At Night, a programme to create and exhibit a collection of stunning photographs and time-lapse videos of the world’s most beautiful and historic sites against a nighttime backdrop of stars, planets and celestial events.

ALMA is being built on the Chajnantor plateau at an altitude of 5000 metres. The observatory, which started Early Science operations on 30 September 2011, will eventually consist of 66 antennas operating together as a single giant telescope. This international astronomy facility is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.



5 December 2011

The VLT’s Next-generation Laser Launch Telescope

This telescope is an important new component of the Four Laser Guide Star Facility, which will sharpen the already excellent vision of ESO’s Very Large Telescope (VLT). Four powerful 20-watt lasers, fired to an altitude of 90 kilometres up in the atmosphere, will help the VLT correct the image distortion caused by turbulence in the air. The Netherlands Organisation for Applied Scientific Research (TNO) is developing the launch telescopes through which the laser beams will be fired. The first of these laser launch telescopes — known as the Optical Tube Assembly — is seen here in the cleanroom at TNO’s Van Leeuwenhoek Laboratory in Delft, the Netherlands, having recently held its Acceptance Review. A special anti-reflective coating gives the lens on the telescope a distinctive blue hue. The photograph was taken by Fred Kamphues, who appears on the left. He is project manager for the Optical Tube Assembly, and is also a new ESO Photo Ambassador. On the right is system engineer Rens Henselmans.

The Four Laser Guide Star Facility is part of the next generation Adaptive Optics Facility, to be installed on the VLT’s 4th Unit Telescope, Yepun, in 2013. Adaptive optics systems rapidly adjust a deformable mirror to counteract the distorting effect of atmospheric turbulence — the same effect that makes stars twinkle — in real time. To do this, they use a guide star as a reference, since the star should appear as a sharp point when the effect of the atmosphere is removed. This lets the telescope make images almost as sharp as if it were in space.

ESO has led the way in adaptive optics systems, having used them for over 20 years on its telescopes. The first such system on the VLT was installed just over ten years ago (see eso0137). In early 2006, the technology was improved with the first use of a laser guide star at the VLT. The unit projects a high-power laser beam into the sky, which excites a layer of sodium atoms at an altitude of 90 kilometres in the atmosphere and makes them glow. This glowing spot acts as an artificial guide star which can be positioned at will in the sky, so astronomers are not restricted to observations close to a sufficiently bright natural guide star (eso0607).

The next generation Four Laser Guide Star Facility will use four such artificial stars, to improve the removal of atmospheric turbulence over a wider field of view. The technology will also serve as a testbed ahead of the construction of the future European Extremely Large Telescope, which will also have multiple laser guide star units.


28 November 2011

A Galaxy Full of Surprises — NGC 3621 is bulgeless but has three central black holes

This image, from ESO’s Very Large Telescope (VLT), shows a truly remarkable galaxy known as NGC 3621. To begin with, it is a pure-disc galaxy. Like other spirals, it has a flat disc permeated by dark lanes of material and with prominent spiral arms where young stars are forming in clusters (the blue dots seen in the image). But while most spiral galaxies have a central bulge — a large group of old stars packed in a compact, spheroidal region — NGC 3621 doesn’t. In this image, it is clear that there is simply a brightening to the centre, but no actual bulge like the one in NGC 6744 (eso1118), for example.

NGC 3621 is also interesting as it is believed to have an active supermassive black hole at its centre that is engulfing matter and producing radiation. This is somewhat unusual because most of these so-called active galactic nuclei exist in galaxies with prominent bulges. In this particular case, the supermassive black hole is thought to have a relatively small mass, of around 20 000 times that of the Sun.

Another interesting feature is that there are also thought to be two smaller black holes, with masses of a few thousand times that of the Sun, near the nucleus of the galaxy. Therefore, NGC 3621 is an extremely interesting object which, despite not having a central bulge, has a system of three black holes in its central region.

This galaxy is located in the constellation of Hydra (The Sea Snake) and can be seen with a moderate-sized telescope. This image, taken using B, V, and I filters with the FORS1 instrument on the powerful VLT, shows striking detail in this odd object and also reveals a multitude of background galaxies. A number of bright foreground stars that belong to our own Milky Way are also visible.

21 November 2011

A Double Green Flash

At sunset, the sky is often painted with an array of oranges, reds and yellows, and even some shades of pink. There are, however, occasions when a green flash appears above the solar disc for a second or so. One such occurrence was captured beautifully in this picture taken from Cerro Paranal, a 2600-metre-high mountain in the Chilean Atacama Desert, by ESO Photo Ambassador Gianluca Lombardi. Cerro Paranal is home to ESO’s Very Large Telescope.

The green flash is a rather rare phenomenon; seeing such a transient event requires an unobstructed view of the setting (or rising) Sun and a very stable atmosphere. At Paranal the atmospheric conditions are just right for this, making the green flash a relatively common sight (see for example eso0812). But a double green flash such as this one is noteworthy even for Paranal.

The green flash occurs because the Earth’s atmosphere works like a giant prism that bends and disperses the sunlight. This effect is particularly significant at sunrise and sunset when the solar rays go through more of the lower, denser layers of the atmosphere. Shorter wavelength blue and green light from the Sun is bent more than longer wavelength orange and red, so it appears slightly higher in the sky than orange or red rays from the point of view of an observer.

When the Sun is close to the horizon and conditions are just right, a mirage effect related to the temperature gradient in the atmosphere can magnify the dispersion — the separation of colours — and produce the elusive green flash. A blue flash is almost never seen as the blue light is scattered by molecules and particles in the dense blanket of air towards the horizon.

The mirage can also distort the shape of the Sun and that of the flash. We see two bands of green light in this image because the weather conditions created two alternating cold and warm layers of air in the atmosphere.

This stunning photo was taken by ESO Photo Ambassador Gianluca Lombardi on 28 March 2011. The phenomenon was captured on camera as the Sun was setting on a sea of clouds below Cerro Paranal.

14 November 2011

Working at ALMA, Day and Night

In the foothills of the Chilean Andes, at an altitude of 2900 metres, the Operations Support Facility (OSF) for the Atacama Large Millimeter/submillimeter Array (ALMA) is a hive of activity. This photograph shows engineers moving a heavyweight antenna at night — with the help of a special 28-wheel transporter — and illustrates how work at ALMA continues around the clock. The antenna, one of 25 provided for the ALMA project by ESO, is being moved into position next to antennas from the other ALMA partners to be tested and equipped with highly sensitive detectors.

When completed, ALMA will consist of 66 12-metre and 7-metre antennas that will work together as a giant radio telescope observing at millimetre and submillimetre wavelengths. The facility will allow astronomers to study our cosmic origins by probing the first stars and galaxies, and imaging the formation of planets.

The telescope is being constructed on Llano de Chajnantor, a plateau that is a 28-kilometre drive from the OSF, at the even higher altitude of 5000 metres. Since the photograph was taken, this antenna has joined others on Chajnantor and has been taking part in ALMA’s first science observations.

While the plateau’s elevated location gives it the extremely dry conditions that are vital for observing at millimetre and submillimetre wavelengths, the altitude make it less pleasant for people working there. Therefore, the people working on ALMA do as much as possible from the lower altitude of the OSF, where work continues day and night. Not only are astronomers and engineers working in shifts and controlling the telescope on Chajnantor remotely, but this is also where the antennas are assembled and tested, and where they are brought for occasional maintenance.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

7 November 2011

GRAAL on a Quest to Improve HAWK-I's Vision

This image shows some of the GRAAL instrument team, inspecting GRAAL’s mechanical assembly in the integration hall of ESO’s Headquarters in Garching bei Munchen, Germany. GRAAL, which will be installed on ESO’s Very Large Telescope (VLT) on Cerro Paranal in Chile, is designed to improve the vision of the VLT’s already excellent HAWK-I camera even further.

GRAAL stands for GRound layer Adaptive optics Assisted by Lasers. It will use the technique of adaptive optics to improve the quality of images by compensating for turbulence in the lower layers of the atmosphere, up to an altitude of 1 kilometre.

GRAAL will form part of the observatory’s next generation Adaptive Optics Facility (AOF). The VLT already uses a powerful laser beam to create an artificial guide star, 90 kilometres up in the atmosphere. The current adaptive optics systems use this guide star as a reference to remove the effect of turbulence in the atmosphere, giving sharper observations, almost as though the telescope were in space.

The next generation AOF, however, will have no fewer than four laser guide stars, launched from Yepun, the VLT’s fourth Unit Telescope. GRAAL captures their light with four sensors, and then adjusts the shape of a deformable mirror up to 1000 times per second to compensate for the blurring effect of the atmosphere. This mirror — part of the AOF upgrade — is in fact a complete replacement for the 1.1-metre secondary mirror of the telescope, and will be the largest deformable mirror yet made. Combined with the multiple guide stars of the laser launching facility, it allows for better corrections over a wider field of view.

GRAAL will be attached to the High Acuity Wide field K-band Imager (HAWK-I), already installed on Yepun. Currently, HAWK-I operates without adaptive optics. Installing GRAAL will improve the sharpness of HAWK-I’s images, and reduce the exposure times needed by up to a factor of two.

After recent successful testing of the main parts of its mechanical assembly, GRAAL’s optics are now being assembled at ESO’s Headquarters. The instrument is expected to reach Paranal at the end of 2013.


31 October 2011

Twinkle Twinkle Little Star

A glowing laser shines forth from the European Southern Observatory’s Very Large Telescope. Piercing the dark Chilean skies, its mission is to help astronomers explore the far reaches of the cosmos. ESO Photo Ambassador Gerhard Hüdepohl was on hand to capture the moment in a stunning portrait of modern science in action. 

We have all gazed up at the night sky and seen the stars gently twinkle as the Earth’s turbulent atmosphere causes their light to shimmer. This is undoubtedly a beautiful sight, but it causes problems for astronomers, who want the crispest possible views. To help them achieve this, professional stargazers use something that sounds as though it has come from science fiction: a laser guide star that creates an artificial star 90 km above the surface of the Earth.

The method by which it achieves this is nothing short of remarkable. The laser energises sodium atoms high in the Earth’s mesosphere, causing them to glow and creating a bright dot that to observers on the ground appears to be a man-made star.

Observations of how this “star” twinkles are fed into the Very Large Telescope’s adaptive optics system, controlling a deformable mirror in the telescope to restore the image of the star to a sharp point. By doing this, the system also compensates for the distorting effect of the atmosphere in the region around the artificial star. The end result is an exceptionally crisp view of the sky, allowing ESO astronomers to make stunning observations of the Universe, almost as though the VLT were above the atmosphere in space.


24 October 2011

Portrait of an Imperfect but Beautiful Spiral

Not all spiral galaxies have to be picture-perfect to be striking. Messier 96, also known as NGC 3368, is a case in point: its core is displaced from the centre, its gas and dust are distributed asymmetrically and its spiral arms are ill-defined. But this portrait, taken with the FORS1 instrument on ESO’s Very Large Telescope, shows that imperfection is beauty in Messier 96. The galaxy's core is compact but glowing, and the dark dust lanes around it move in a delicate swirl towards the nucleus. And the spiral arms, patchy rings of young blue stars, are like necklaces of blue pearls.  

Messier 96 lies in the constellation of Leo (The Lion). It is the largest galaxy in the Leo I group of galaxies; including its outermost spiral arms, it spans some 100 000 light-years in diameter — about the size of our Milky Way. Its graceful imperfections likely result from the gravitational pull of other members in the group, or are perhaps due to past galactic encounters. 

A multitude of background galaxies peers through the dusty spiral. Perhaps the most striking of these objects is an edge-on galaxy that — because of a chance alignment — appears to interrupt the outermost spiral arm to the upper left of Messier 96's core.

This image was processed by ESO using the observational data found by Oleg Maliy from Ukraine, who participated in ESO's Hidden Treasures 2010 astrophotography competition [1], organised in October–November 2010, for everyone who enjoys making beautiful images of the night sky using astronomical data obtained with professional telescopes. The image was made with data taken at visible and infrared wavelengths through B, V, and I filters. 


[1] ESO’s Hidden Treasures 2010 competition gave amateur astronomers the opportunity to search through ESO’s vast archives of astronomical data, hoping to find a well-hidden gem that needed polishing by the entrants. To find out more about Hidden Treasures, visit http://www.eso.org/public/outreach/hiddentreasures/.

17 October 2011

Stars Dancing Above the VLT

The night sky above the 2600-metre-high Cerro Paranal in the Atacama Desert in Chile is dark and clear. So clear, that very long sequences of photos can easily be taken without a single cloud obscuring the stars as they rotate around the southern celestial pole.

The site is home to ESO’s Very Large Telescope (VLT) array. Its four 8.2-metre Unit Telescopes dominate this image made by Farid Char, a student at Chile’s Universidad Católica del Norte. One of the smaller Auxiliary Telescopes is also visible, hiding in the background in the bottom left corner.

But the star of the show is the striking starry sky. Made by combining 450 exposures of 20 seconds each, the image captures the apparent stellar movement during two and a half hours. This movement, signalled by dotted trails, is illusory: the Earth, and not the stars, is rotating as time goes by.

The sequence has also captured the Unit Telescopes as they observe different objects in the night sky over the hours, transforming their precise motions into a seemingly frenetic blur of activity. What’s more, one of the exposures has even caught a shooting star, seen as a small trail above the Auxiliary Telescope in the bottom left of the image.


10 October 2011

Flying above the ALMA Site: The Operations Support Facility

This spectacular aerial view shows the ALMA Operations Support Facility (OSF), located 2900 metres above sea level in the foothills of the Chilean Andes, near San Pedro de Atacama.

ALMA, the Atacama Large Millimeter/submillimeter Array, is currently under construction on the 5000-metre-high Chajnantor plateau. Such a high altitude site is necessary for ALMA’s array of antennas to observe the Universe in millimetre and submillimetre radiation, but the lack of oxygen makes the Array Operations Site (AOS) a very uncomfortable place for people to work. For this reason, as much of the scientific and technical work as possible takes place at the OSF, which is 2100 metres lower in altitude. The antennas are even controlled remotely from the OSF.

In this picture, from the bottom left to the centre right, the North American, the Japanese and the European antenna assembly facilities are clearly distinguishable. In these areas, the antennas are assembled and tested by the partners and their contractors, before being handed over to the Joint ALMA Observatory. At this point, the antennas are moved to the area next to the main OSF building, which is visible in the centre of the picture. Here, they undergo further testing before being transported to the AOS along the 28-kilometre road, which leads off to the right of this image. The camp, which offers accommodation for the personnel working at the site, is seen on the left. In the background, the snow-capped high volcanoes of the Andes are silhouetted against the vivid blue sky. The distinctive conical shape of the volcano Licancabur is clearly recognisable.

The ALMA project is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ESO is the European partner in ALMA.


3 October 2011

VLT Observes the Antennae Galaxies

A new Very Large Telescope (VLT) image of the Antennae Galaxies gives us what may be the second-best visible-light view yet of this striking pair of colliding galaxies with dramatically distorted shapes. This amazing object takes its name from the long antenna-like "arms" extending far out from the nuclei of the two galaxies, best seen in wider-field images by ground-based telescopes such as the one at this link.

This VLT view focuses instead on the galaxies’ nuclei, where the real action is taking place as the two galaxies merge into a single giant galaxy. Spurred by shock waves created by their gravitational wrestling, the two galaxies have become dotted with brilliant blue hot young stars in star-forming regions, surrounded by glowing hydrogen gas, shown here in pink. The two pale yellow blobs are the cores of the original galaxies, shining with the light of old stars and picked out by delicate lanes of dust. 

The Antennae Galaxies were immortalised in 2006 by one of the NASA/ESA Hubble Space Telescope’s most famous images (composed by ESA’s Hubble group residing at ESO).

If you are hungry for more information about this amazing object, read the just-published ESO press release about the first image from ALMA, the Atacama Large Millimeter/submillimeter Array, which has just started its Early Science observations. ALMA , constructed by ESO and its international partners, observes the Universe in light with millimetre and submillimetre wavelengths — radically different from visible-light and infrared telescopes. ALMA’s view is the best submillimetre-wavelength image ever made of the Antennae Galaxies, despite being just a taster of what ALMA will deliver. The ALMA image was made using test data from only twelve antennas, and as the observatory grows, the sharpness, efficiency, and quality of its observations will increase dramatically.

This image was processed by ESO using the observational data found by Alberto Milani (Italy), who submitted it to ESO’s "Your ESO Pictures" Flickr group.

26 September 2011

All Four VLT Unit Telescopes Working as One

When light from all four 8.2-metre Unit Telescopes of ESO’s Very Large Telescope (VLT) in Cerro Paranal on 17 March 2011 was successfully combined for the first time (ann11021), ESO Photo Ambassador Gerhard Hüdepohl was there to capture the moment.

Having all four of the Unit Telescopes (UTs) working as one telescope observing the same object was a major step in the development of the VLT. While mostly used for individual observations, the UTs were always designed to be able to operate together as part of the VLT Interferometer (VLTI).

All the UTs are pointed in the same direction, at the same object, although this isn’t obvious because of the wide-angle lens used to take the photo. The light collected by each of the telescopes was then combined using an instrument called PIONIER [1]. When combined, the UTs can potentially provide an image sharpness that equals that of a telescope with a diameter of up to 130 metres.

Two of the four 1.8-metre Auxiliary Telescopes, which are also part of the VLTI, can be seen in the picture together with the UTs. While the larger telescopes are fixed, these smaller instruments, in round enclosures, can be relocated to 30 different stations. With the ATs as part of the VLTI, astronomers can capture details up to 25 times finer than with a single UT.

Gerhard Hüdepohl has lived in Chile since 1997. Aside from taking stunning photos in the Atacama Desert, he works as an electronics engineer at the VLT.


[1] PIONIER, developed at LAOG/IPAG in Grenoble, France, is a visiting instrument at the Paranal Observatory. PIONIER is funded by Université Joseph Fourier, IPAG, INSU-CNRS (ASHRA-PNPS-PNP) ANR 2G-VLTI ANR Exozodi. IPAG is part of the Grenoble Observatory (OSUG).


19 September 2011

The “Little World” of Paranal

This interpretation of a previous Picture of the Week was created by astronomer Alex Parker. It captures some of the essence of Paranal Observatory — a little world where astronomers leave the Earth behind and travel to the stars... metaphorically at least.

The observatory lies deep in the barren Atacama Desert, which can really seem like an alien environment. It is far from civilisation and modern life, a place where visiting astronomers spend their nights gazing out at the wonders of the Universe using ESO’s flagship facility, the Very Large Telescope (VLT). The VLT is the reason why Cerro Paranal was transformed from just another mountain in the Chilean Andes into a base for world-class scientific research.

When night falls over Paranal, and the night sky is aglow with stars, nebulae and nearby galaxies, the unearthly view emphasises our place in the Universe — as Alex Parker so creatively demonstrates — floating through space on a tiny chunk of rock.

Have you made something special using ESO’s images or video? Let us — and other ESO fans — know through our new Flickr group, called Your ESO Pictures.


12 September 2011

Red Moon Rising

Deep in the heart of the Atacama Desert, home of the Paranal Observatory, the Sun is setting at the start of another clear night. This charming photograph, taken by ESO Photo Ambassador Gianluca Lombardi shows one of four Auxiliary Telescopes (ATs) that belong to ESO’s Very Large Telescope (VLT) sitting boldly against a vivid sky of pink and blue. The full Moon, seen hovering over the horizon, has a distinctly reddish hue, a phenomenon caused by the scattering of light by Earth’s atmosphere.

When the Moon is close to the horizon, the light we see from it must travel through a greater thickness of the atmosphere, so the effects of scattering are increased. As red light is more resilient to scattering than green or blue, our view of the Moon is reddened. As it happens, the reddening effect is somewhat less pronounced at sites like Paranal, as the clear air contains fewer particles that cause scattering. In addition to this, Paranal’s isolated location, far from civilisation and hence sources of light pollution, makes it a perfect place for ground-based astronomy.

The 1.8-metre Auxiliary Telescopes are integral to the VLT Interferometer (VLTI). Whereas the Unit Telescopes are very often engaged in independent activities, the ATs devote all their time to the interferometer. One advantage of this is that the ATs can be used for regular, long-term monitoring observations, which allow exceptionally precise measurements to be made of object positions; this is known as the Narrow Angle Astrometry mode of the VLTI. The ATs telescopes are mobile and able to relocate between 30 different observing positions. By utilising the entire Paranal platform this way, a separation of 202 metres between ATs is possible — the longest baseline of the VLTI.


5 September 2011

Laser Meets Lightning

As ESO tested the new Wendelstein laser guide star unit by shooting a powerful laser beam into the atmosphere, one of the region’s intense summer thunderstorms was approaching — a very visual demonstration of why ESO’s telescopes are in Chile, and not in Germany. Heavy grey clouds threw down bolts of lightning as Martin Kornmesser, visual artist for the ESO outreach department, took time-lapse photographs of the test for ESOcast 34. With purely coincidental timing this photograph was snapped just as lightning flashed, resulting in a breathtaking image that looks like a scene from a science fiction movie. Although the storm was still far from the observatory, the lightning appears to clash with the laser beam in the sky.

Laser guide stars are artificial stars created 90 kilometres up in the Earth’s atmosphere using a laser beam. Measurements of this artificial star can be used to correct for the blurring effect of the atmosphere in astronomical observations — a technique known as adaptive optics. The Wendelstein laser guide star unit is a new design, combining the laser with the small telescope used to launch it in a single modular unit, which can then be placed onto larger telescopes.

The laser in this photograph is a powerful one, with a 20-watt beam, but the power in a bolt of lightning peaks at a trillion (one million million) watts, albeit for just a fraction of a second! Shortly after this picture was taken the storm reached the observatory, forcing operations to close for the night. While we may have the ability to harness advanced technology for devices such as laser guide stars, we are still subject to the forces of nature, not least among them the weather!



29 August 2011

First 7-metre ALMA Antenna Arrives at Chajnantor

The first of twelve 7-metre diameter ALMA antennas has just been transported on 24 August 2011 to the 5000-metre-high Chajnantor plateau, where the Atacama Large Millimeter/submillimeter Array (ALMA) is under construction. ALMA is a giant radio telescope composed of an array of fifty 12-metre antennas, as well as a smaller array known as the Atacama Compact Array (ACA). This will have a total of four 12-metre antennas and the twelve 7-metre dishes.

The four 12-metre ACA antennas have already been moved up to the high plateau, but this is the first of the smaller 7-metre dishes — which put the “compact” into Atacama Compact Array — to reach Chajnantor. It is seen in the centre of this photograph, surrounded by some of the other ALMA antennas. Penitentes ice formations are seen in the foreground.

The larger 12-metre antennas of the main array cannot be placed closer than 15 metres apart as they would otherwise bump into each other. This minimum separation between antennas governs the maximum scale of the features that they can detect in the sky. This means that the main array cannot observe the broadest features of extended objects such as giant clouds of molecular gas in the Milky Way, or nearby galaxies. The ACA is specifically designed to help ALMA make better observations of these extended objects. Its smaller 7-metre antennas can be placed closer together, making them better able to measure the broader structures that the main array misses.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

All of the ACA antennas are being provided by Japan through a contract with MELCO (Mitsubishi Electric Corporation). ALMA will also have 25 12-metre antennas provided by ESO, and 25 by NRAO.


22 August 2011

Flying over the ALMA Site: The Array Operations Site

ALMA, the Atacama Large Millimeter/submillimeter Array, will be initially composed of 66 antennas, designed to observe the Universe in millimetre and submillimetre radiation. The main array will consist of fifty 12-metre antennas that can be spread over distances from 150 metres to 16 kilometres. In addition to the main array, ALMA will also have a compact array, composed of four 12-metre antennas plus twelve 7-metre antennas. By using the technique of interferometry, ALMA will work as a single giant telescope, enabling astronomers to observe the cold universe with unprecedented sensitivity and resolution. From the high altitudes of the Andes, ALMA will provide a revolutionary contribution to the search for our cosmic origins.

ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

15 August 2011

As Time Goes By

Just as the Sun rises in the east and sets in the west, so do the stars appear to slowly march across the sky. Their leisurely pace is imperceptible to a casual observer, but you can test the effect for yourself: on the next clear night note the position of a bright star, and then check again a few hours later. The change is not caused by the motion of the stars themselves, but rather the rotation of the Earth.

Long-exposure photography is the ideal way to capture this motion. A camera is set up on a tripod, and the shutter opened to the sky. Normal snapshots gather light for a fraction of a second, but these special images need starlight to pour onto them for much longer, like a bucket collecting rainwater.

To obtain this image, ESO Photo Ambassador Gianluca Lombardi collected light for a total of 25 minutes. This may not seem like a long time, but the streaks of light in the night sky tell a different story.  The Earth has rotated so that the pin-pricks of starlight have become star trails. In the top left, the trails form arcs around the southern celestial pole, which is outside the photograph. The ghostly traces of someone walking across the Paranal observing platform can also be seen.

Many familiar and outstanding pictures of astronomical objects are obtained using the same principle of accumulating light over a long period of time to build up an image. It is common for telescopes to gather light for several hours to make a single picture. This brings with it an additional challenge: the Earth rotating means that the telescope must also move to keep track of its target.


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