Picture of the Week 2023

25 September 2023: It’s hard not to get sucked into this Picture of the Week, taken using a long exposure at ESO’s Paranal Observatory in the Chilean Atacama Desert. Above the mountaintop observatory, a spectacular dance is playing out: imaged over several hours, stars appear to make their way in long arcs, called star trails, across the night sky. Paranal is home to one of the world’s most advanced optical telescopes: ESO’s Very Large Telescope, or VLT. This flagship facility actually consists of four Unit Telescopes and four smaller movable Auxiliary Telescopes, like the one in the foreground on the right. But what are those mysterious beams of orange light erupting from one of the Unit Telescopes? Well, they’re for making stars, kind of. The Four Laser Guide Star Facility propagates laser beams[1] into the sky, making sodium atoms in the upper atmosphere glow like artificial stars. Each laser delivers 22 watts of ...

18 September 2023: This Picture of the Week shows the unique stellar system HIP 81208, as captured by ESO’s Very Large Telescope (VLT) in Chile. Astronomers thought HIP 81208 was a system consisting of a massive central star (A, the central bright spot), a brown dwarf (B) circling around it, and a low-mass star (C) orbiting further away. However, a new study has revealed a never-before-seen hidden gem: an object (Cb), approximately 15 times more massive than Jupiter, orbiting around the smaller of the two stars (C). The discovery of Cb means that HIP 81208 is a uniquely intriguing system with two stars and two smaller bodies orbiting each one –– in other words, a hierarchical quadruple system. The mass of the newly found Cb object places it right at the border between planets and brown dwarfs –– failed stars that are not massive and hot enough to fuse hydrogen into helium. The ...

11 September 2023: There are several galaxies in this Picture of the Week, but the most fascinating is probably the one surrounded by four light-blue dots, resembling a flower with blue petals. But, are these dots real? Yes and no… Taken with ESO’s Very Large Telescope (VLT), this image shows a so-called Einstein Cross. The four ‘petals’ are images of a distant galaxy hidden behind the orange galaxy at the centre. Something very fascinating happens to allow us to detect the light from this hidden object: the galaxy at the centre acts as a gravitational lens, bending the light emitted from the distant galaxy around it. As a result, we see several images of the distant galaxy, distorted and magnified. In the special configuration of these two galaxies, the hidden one appears as four images around the central ‘lens’ galaxy, forming a cross-like (or flower-like) pattern dubbed an Einstein Cross. Gravitational lensing thus ...

4 September 2023: It might look like the opening scene from The Lion King, but this stunning Picture of the Week was actually taken in the Chilean Atacama Desert rather than the African savannas. Taking centre stage is ESO’s Extremely Large Telescope (ELT), or part of it, at least. The ELT’s steel dome is about 80 metres tall and one day it will play host to the world’s biggest eye on the sky. When finished, the dome will weigh some 6100 tonnes and be capable of rotating 360 degrees on a set of 36 stationary trolleys. This spectacular photograph of the sunrise over Cerro Armazones, the ELT’s perch, was shot on 29 August from around 23 kilometres away on top of another famous mountain: Cerro Paranal, home to the ELT’s older sibling, ESO’s Very Large Telescope, or VLT. You could say the stars were aligned for this image: since the position of the ...

28 August 2023: The flat panorama of the Chajnantor plateau dominates this Picture of the Week. Situated at an altitude of around 5000 metres in the Chilean Andes, this plateau is one of the driest places on Earth — challenging for humans, but perfect for astronomical observations. This breathtaking landscape is home to the Atacama Pathfinder Experiment (APEX), the white structure down in the centre of the image. Inaugurated in 2005, APEX is a 12-metre diameter radio telescope that studies the cold, dusty and distant Universe, and is operated by ESO on behalf of the Max Planck Institute for Radio Astronomy (MPIfR). Now look ahead, towards the distant brown mountains, and you might be able to make out a bunch of white dots. Those are in fact the 66 high-precision antennas of ALMA, the Atacama Large Millimeter/submillimeter Array, operated by ESO together with its international partners. Like APEX, ALMA’s antennas observe the coldest ...

21 August 2023: Welcome to ESO’s La Silla Observatory, home to several telescopes since the 1960s and the setting of this Picture of the Week. Located 600 km north of Chile’s capital Santiago, La Silla sits at around 2400 meters above sea level. More than just the telescopes live at this idyllic location: the staff who run them do too. Astronomers, engineers and support staff spend shifts of several days working on-site, and the buildings in the foreground allow them to live, work and relax in the harsh conditions of the Atacama desert. The building at the centre contains bedrooms, a canteen, a gym and a cinema room, among other facilities. On the left we can see dormitories where visiting astronomers can rest after a long night observing the cosmos. Meanwhile, the long white building right at the bottom is the New Operations Building, from which the New Technology Telescope (NTT), ESO 3.6-metre ...

14 August 2023: This Picture of the Week — taken with ESO’s Visible and Infrared Survey Telescope (VISTA) at Paranal Observatory in Chile — might look like a scene from a snowy winter's night, but it’s not. It’s an infrared image of NGC 6723, a globular cluster located about 28 000 light years from Earth in the constellation Sagittarius. Globular clusters are spherical-shaped groups of stars, tightly bound together by gravity. Their name is derived from the Latin word globulus, meaning small sphere — somewhat misleading given that NGC 6723, as most globular clusters, contains hundred of thousands to millions of stars. So far, astronomers have found more than 150 globular clusters in our galaxy, the Milky Way, with most of them estimated to be at least 10 billion years old and hosting some of the oldest stars in the galaxy. Globular clusters were key to pinpointing our own location within the Milky ...

7 August 2023: It’s now close to 80 metres high — the mammoth steel structure of the ESO’s Extremely Large Telescope (ELT) dome is taking shape in this Picture of the Week, taken on 2 August 2023 under the light of the full Moon. Right now, engineers and construction workers are assembling the structure of the telescope dome in the Chilean Atacama Desert, with progress visible almost every day. When completed, the ELT will be the world’s biggest eye on the sky for visible and infrared observations. Overall, the ELT project is now more than 50 percent complete. The dome structure visible here will house a pioneering five-mirror optical design, which includes a giant main mirror (M1), 39 metres wide and made up of 798 hexagonal segments. The telescope mirrors and other components are being built by companies in Europe, where work is progressing well too. All of the other systems needed to ...

31 July 2023: Can you see ESO’s New Technology Telescope (NTT) peaking out of its enclosure on the right of this Picture of the Week? When this telescope was inaugurated in 1989 it packed innovative technology that laid the foundations for all ground-based telescopes that would follow. The mirrors of professional telescopes are so large and heavy that they bend under their own weight; if left uncorrected, this would yield distorted images. The NTT, which is located at ESO’s La Silla Observatory in Chile, has a flexible main mirror that can change shape during observations. Using a so-called ‘reference star’, the NTT adjusts the mirror's shape to correct these deformations, thus ensuring optimal image quality. This technique, called active optics (not to be confused with adaptive optics) was developed by the late Raymond Wilson at ESO. Today, it is applied to all major modern telescopes, including ESO’s Very Large Telescope (VLT) at Cerro ...

24 July 2023: Imagine looking through your door’s peephole and seeing this! This Picture of the Week shows a fisheye view of the 1.52-metre telescope at ESO’s La Silla Observatory in Chile, one of our first telescopes that is now enjoying a second life. ESO was founded in 1962, and only a few years later the 1.52-metre telescope was inaugurated. This telescope had several spectrographs like the Boller & Chivens, ECHELEC and FEROS, which studied spectacular comets, stars with powerful winds and exciting exoplanets among other things. This pioneering telescope was decommissioned in 2002, and FEROS was moved to the MPG/ESO 2.2-metre telescope also at La Silla, where it still searches for distant new worlds. But this wasn’t the end for the 1.52-m telescope. After a 20-year-long shutdown, the telescope was recommissioned and upgraded in 2022 as part of the PLATO Spec international project, led by a Czech team. It will now study ...

17 July 2023: Can you see the chameleon in this picture? No? Well, it's camouflaged! Yes, we are joking, but this Picture of the Week actually shows the Chamaeleon Cloud, or IC 2631. In the southern hemisphere, this cloud is visible in the sky for most of the year, and in this image, captured by ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA), you can admire it in infrared light. IC 2631 is a reflection nebula made of dust clouds that reflect the light emitted from nearby stars. The nebula is mainly illuminated by one of the youngest, most massive and brightest stars in its neighborhood, HD 97300, visible to the centre-right of the image. The Chamaeleon Cloud is in fact the brightest nebula in the Chamaeleon Complex, a vast region of gas and dust clouds –– much larger than what this image shows –– where numerous newborn and still-forming stars live. ...

10 July 2023: This Picture of the Week shows a beautiful flock of sheep, grazing in the Chilean Andes. No, wait, wait, wait. There's no grass to feed on here, and they are at an altitude of around 5000 metres. Ok, no, they are not sheep. Let’s start again. This Picture of the Week shows the beautiful antennas of the Atacama Large Millimeter/submillimeter Array (ALMA), operated by ESO and its international partners in the Chilean Andes. Ok, that’s better! As you can see, ALMA’s 66 white antennas are not the same size: most of them are 12-metre antennas, and only twelve are 7-metre antennas (see the smaller ones over to the left of the ‘flock’?). They work together as an interferometer, acting like a single big telescope. ALMA observes the light emitted from some of the coldest objects in the Universe, such as the most distant galaxies. These antennas can be physically moved ...

3 July 2023: Have you ever seen so many telescopes all together? This Picture of the Week was taken at sunset at ESO’s La Silla Observatory, suspended over an ocean of mountains and soft, foggy clouds. Nestled in the Chilean Atacama Desert at an altitude of 2400 metres, La Silla is far from sources of light pollution and has one of the darkest skies on Earth, which explains why it's packed full with telescopes! How many can you spot here? Let’s take a closer look at a few of them. Almost at the centre of the frame, ESO’s 3.6-metre telescope stands out, with the smaller dome of the Coudé Auxiliary Telescope attached to it. The 3.6 m telescope is home to one of the world’s best extrasolar planet hunters, the so-called High Accuracy Radial velocity Planet Searcher (HARPS) spectrograph. The antenna to the left side of the picture is the Swedish-ESO Submillimetre Telescope ...

26 June 2023: Take a look at this aerial photo of the Atacama Pathfinder Experiment, or APEX for short, sat stoically atop the Chajnator plateau in Chile’s Atacama Desert. This remote, dry location, some 5100 metres above sea level, is the perfect location to uncover the secrets of the so-called “cold universe”, the regions in space only a few tens of degrees above absolute zero. APEX is a 12-metre telescope hosted and operated by ESO on behalf of the Max Planck Institute for Radio Astronomy (MPIfR). It observes at millimetre and submillimetre wavelengths — between infrared and radio waves — where vast cold clouds of interstellar dust and gas glow. These clouds act as the birthplace for new stars and would be obscured in the visible light range. Light collected by APEX is then recorded by different instruments. One of these, known as the Large APEX Bolometer Camera (LABOCA), has an array of ...

19 June 2023: In Chile’s Atacama desert, ESO’s very own colosseum — the Extremely Large Telescope, or ELT –– is being assembled. As this image taken in early June 2023 shows, progress is moving quickly on the construction site, as the steel frame of the telescope’s dome is pieced together. Parts of the steel backbone running around the edge of the building are fitted together at the ELT base camp before being transported to the platform atop Cerro Armazones using specialised transporters. Not an easy feat given that these pre-assembled steel blocks weigh some 70 tonnes! Once they’re on location, the giant steel Lego-like blocks are hoisted up using the gigantic cranes you see here, and mounted on a rail inserted into trolleys. The entire dome, which will weigh 6,100 tonnes, will rotate on these trolleys when the ELT enters operation. If you peer into the distance, to the right of the yellow ...

12 June 2023: It might look like there’s not a lot going on in this Picture of the Week, but looks can be deceiving. Far off in the distance, huddled together like penguins in an Antarctic storm, sit the 66 high-precision antennas of the Atacama Large Millimeter/submillimeter Array (ALMA). Operated by ESO together with international partners, ALMA is designed to study the light emitted by the coldest objects in the Universe, such as vast cold clouds in interstellar space. Stretching out either side of the antennas is the empty landscape of the Chajnantor plateau. Sitting at 5,000 m above sea level in the Chilean Andes, this remote location is one of the driest places on Earth. It’s this dryness that makes it the perfect place for observing the signals from the cold Universe which would otherwise be heavily absorbed by water vapour in our atmosphere. ALMA is what’s known as an interferometer, meaning ...

5 June 2023: This Picture of the Week shows a long exposure image of the BlackGEM telescopes, located at ESO’s La Silla Observatory in Chile. The whitish star trails in the sky are an effect due to the Earth’s rotation on its axis around the southern celestial pole, which gives the impression of the stars’ movement over the course of several hours. To the right hand side of the central telescope the Milky Way is visible, seen here as a particularly bright region, densely packed with streaks of starlight. As these streaks move in circles across the night sky, the viewer gets a sense of tumbling around inside a giant washing machine, as they peer out at the scene through the fisheye lens. BlackGEM, which recently started operating, is an array of three 0.65-metre optical telescopes, which can point at different regions of the sky, searching for some of the most dramatic events ...

29 May 2023: Sometimes dramatic events are needed to create something stunning. This beautiful structure of filaments and clouds in the southern constellation of Vela are all that remains of a massive star that died in a powerful explosion known as supernova. This is a small section of a larger image taken using the wide-field camera OmegaCAM at the VLT Survey Telescope (VST). Hosted at ESO’s Paranal Observatory in the Chilean desert, the VST is one of the best telescopes in the world to take large images of the sky in visible light. Even though bright stars populate this image, it's hard to not be captivated by the pink gaseous clouds filling up the frame. Some tiny, others thicker, the filaments stretch outwards like tentacles. As they intertwine and cling together, an intricate network is formed which mixes with blurred clouds. But how did they come to be like this? Around 11 000 ...

22 May 2023: A lot can change in more than two decades — just take a look at these pictures of ESO’s Very Large Telescope (VLT)! On the left we see the VLT when it was still under construction atop Cerro Paranal in Chile, while on the right we see it in all its glory as it stands today. Before building the telescopes themselves the mountain had to be lowered by 28 metres to create the telescope platform, which meant removing some 350 000 cubic metres of rock. Then in 1998 the Unit Telescope UT1 (Antu), the leftmost telescope and the furthest along in its construction in the “then” picture, captured its first image of the cosmos — 25 years ago this week. Today, the VLT consists of four Unit Telescopes with main mirrors of 8.2 metres diameter and four movable 1.8-metre diameter Auxiliary Telescopes. After a quarter of a century of observations, ...

15 May 2023: Have you ever seen a sunset so red? Probably not, since the cause of this reddened twilight sky is something quite dramatic: a volcanic eruption. This Picture of the Week was captured at ESO’s Paranal Observatory in Chile; under the Milky Way, on the top of the dark silhouette of Cerro Paranal, ESO’s Very Large Telescope looks upwards to the sky. On 15 January 2022, the submarine volcano Hunga Tonga–Hunga Ha‘apai erupted in the southern Pacific Ocean. This eruption created shock waves that rippled through the atmosphere, reaching places far from the volcano itself. At ESO’s Paranal and La Silla observatories in Chile, more than 10 000 kilometres away, weather stations detected these atmospheric disturbances. The eruption also launched an ash plume 57 kilometres tall, releasing massive quantities of particles into the atmosphere, including water vapour and dust. Sunlight is scattered and reddened by these tiny dust particles, and this ...