Picture of The Week

ESO’s Extremely Large Telescope from space

Mon, 06 Apr 2026 09:00:00 +0200

Like a tiny snail shell lying on a beach, a small spiral juts out from the expanse of the Atacama Desert. While most of the lines carving the landscape in today's Picture of the Week are natural consequences of geology, the circling path is in fact a road leading up the mountain Cerro Armazones. At the top sits ESO's Extremely Large Telescope (ELT), currently under construction, visible only as a black dot below the centre of this image.

Pinpointing the ELT in the vast area of reds and greys might, at first, make its name seem excessive. But it is all a matter of perspective. This photo was taken by Sophie Adenot, a French engineer, helicopter pilot and astronaut at the European Space Agency (ESA), currently on the International Space Station (ISS) for a long-duration mission called εpsilon. Even from her vantage point, more than 400 kilometres above the Earth's surface, the ELT is a distinguishable feature in the landscape. Once completed, it will be the world's largest visible and infrared light telescope. Its immense light-gathering capability will allow the ELT to probe deeper into the Universe than ever before. An avid stargazer herself, Adenot has sent a log from the ISS to explain why the ELT's location was chosen:

Day 051, orbit 802 – Chile has some of the most beautiful skies on Earth... Stargazing takes on a different dimension there, with three galaxies perfectly visible to the naked eye in the night sky – our very own Milky Way and its two neighbours, the large and small Magellanic Clouds.

The Mars-like Atacama desert is home to several of ESO’s observatories, including at La Silla and Cerro Paranal. This picture shows the construction site of ESO’s Extremely Large Telescope (ELT) on Cerro Armazones. Once completed, the ELT will become the world’s biggest eye on the sky, featuring a 39-meter-diameter mirror… that’s about 9 cars parked bumper-to-bumper, or two H225 helicopters nose-to-tail!

Collaboration between Europe and Chile at its best!

An ExTrA sphere

Mon, 30 Mar 2026 06:00:00 +0200

Two sunlit spheres can be seen in today's Picture of the Week. While these orbs share similarities in their shape and in being illuminated by the same star, they are vastly different. The one farthest away from the camera, hiding behind the clouds, is our own Moon, the Earth's only natural satellite. The other object is the dome of a telescope at ESO's La Silla Observatory, located in the outskirts of the Atacama Desert, in northern Chile.

The telescope is one of the three in the French project Exoplanets in Transits and their Atmospheres (ExTrA). ExTrA is focused on detecting Earth-sized worlds in the Milky Way. It relies on the transit method, where planets block a fraction of the light from the star they orbit when passing between it and Earth, just like a partial eclipse. ExTrA centres on worlds orbiting red dwarfs –– stars much smaller, colder and dimmer than the Sun. Because red dwarfs are small, planets crossing in front of them block more light, making them easier to find than planets orbiting regular stars.

Who knows, perhaps some of these planets may look as otherworldly as the landscape of this picture. “These places compel me every time to think about our position in the Universe, putting my life ‘in context’ so to say,” says the photographer, ESO astronomer Luca Sbordone. “It always brings me peace.”

The Triangulum galaxy up close

Mon, 23 Mar 2026 06:00:00 +0100

Today’s Picture of the Week is a closeup of the nearby Triangulum galaxy, also known as Messier 33, located about 3 million light-years away. This festive-looking image, taken with ESO’s Very Large Telescope (VLT), reveals the diversity and complexity of the gas and dust between the stars in great detail.

Stars are not, as is often imagined, isolated spheres in the dark, but rather live in rich and complex environments that they actively shape. Studying this cosmic interplay tells us about how stars form, and how their radiation affects the surrounding material, which helps us to understand how galaxies evolve as a whole.

The image was presented in a new study led by Anna Feltre, a postdoctoral researcher at the INAF-Astrophysical Observatory of Arcetri, Italy. The team used data taken with the Multi Unit Spectroscopic Explorer (MUSE) instrument at the VLT. MUSE’s superpower is its ability to break up the light into the different rainbow colours, allowing the team to examine the chemical composition of the interstellar matter at every location across its whole field of view.

The different colours of the image represent different elements: blue, green and red indicate the presence of oxygen, hydrogen and sulphur, respectively. MUSE allowed the team to map the distribution of many other elements, as well as their motion, key to understanding the link between stars and their surroundings. As Feltre aptly puts it: “This cosmic interplay produces a spectacular and dynamic landscape, revealing that the birthplaces of stars are far more beautiful and complex than we ever imagined.”

Reaching for the stars

Mon, 16 Mar 2026 06:00:00 +0100

The dark sky provides the perfect backdrop for today's Picture of the Week, captured by Chilean astrophotographer Alexis Trigo. The spotlight is on the magnificent Unit Telescope 1, also known as Antu, part of ESO’s Very Large Telescope (VLT). Hiding behind it is another almost identical telescope, called UT4 or Yepun, reaching for the stars with its laser beams. In the background, the Milky Way stretches low in the horizon.

The VLT comprises four Unit Telescopes, each with an 8.2 m mirror. All four UT domes are as big as a family house, keeping the telescope safe and sound from all environmental conditions. But despite their similarities, Yepun is special, as it is the only UT with a total of four lasers.

Lasers create artificial stars in Earth's upper atmosphere, allowing astronomers to measure and correct for atmospheric turbulence that blurs their data. Initially, only UT4 had lasers installed, but this changed recently with the completion of the GRAVITY+ upgrade to the VLT Interferometer. Now, a laser has been installed on all the other three UTs. Nevertheless, Yepun remains distinctive with its four lasers, delivering crystal-clear views of the cosmos.

New look at the stars around the Milky Way's centre

Mon, 09 Mar 2026 09:00:00 +0100

A new view on the heart of our Milky Way is presented in today's Picture of the Week. This stunning snapshot, taken with ESO’s Very Large Telescope (VLT), reveals the stars and gas surrounding an invisible giant — a supermassive black hole, located some 27 000 light-years away. This is a hugely dynamic environment, with stars and gas clouds hurtling by the black hole at dramatic speeds.

A team of astronomers at the Max Planck Institute for Extraterrestrial Physics in Germany has detected a new gas cloud, named G2t, orbiting the supermassive black hole. Two gas clouds, G1 and G2, were already known, but their nature and origin were still being debated. In particular, it was unclear whether these clouds were hiding a star inside or consisted purely of gas. However, the discovery of a third gas cloud now helps answer these questions.

The observations were done with the Enhanced Resolution Imager and Spectrograph (ERIS), an instrument on ESO’s VLT that can not only take images like the one in this Picture of the Week, but also spectra. Thanks to this, astronomers were able to measure the 3D orbits of the clouds around the black hole. The clouds move within a very small region at the centre of this wide-field image. It was revealed that G1, G2 and G2t are actually on almost identical orbits, only rotated a bit with respect to each other. This rules out the possibility that each cloud hides a star in their core, as the odds of different stars having almost identical orbits are slim. The similarity of the orbits suggests that the three clouds probably share the same origin, most likely IRS16SW, a pair of massive stars expelling an enormous amount of gas. As IRS16SW moves around the black hole, each cloud of gas is ejected in a slightly different orbit, explaining the small differences in the trajectories of the ‘G-triplet’.

This discovery shows that, despite decades of monitoring our Milky Way centre, new unanswered curiosities still arise. But what could be more exciting than mysteries waiting to be solved?

A cosmic hawk and its baby stars

Mon, 02 Mar 2026 06:00:00 +0100

Today’s Picture of the Week, taken with ESO’s Very Large Telescope (VLT), seems to have captured a cosmic hawk as it spans its wings. While the dark clouds in the middle of the image make up the head and body of the bird of prey, the filaments extending away from the body to the left and right compose its wings. Below it, is a mesmerising blue nebula with massive newly born stars, whose intense radiation make the gas around them glow brightly.

Altogether the image shows the RCW 36 nebula, located about 2300 light-years away in the Vela constellation. Coincidently, this nebula, resembling a hawk, was also captured by a hawk — the HAWK-I instrument on the VLT. While the most apparent stars in this image may be the massive and bright baby stars, the astronomers behind this image are actually more interested in hidden, very dim stars called brown dwarfs — “objects unable to fuse hydrogen in their cores,” explains Afonso do Brito do Vale, a PhD student at the Instituto de Astrofísica e Ciências do Espaço, Portugal, and the Laboratoire d'Astrophysique de Bordeaux, France, and lead author of a new paper where this image was presented.

HAWK-I is perfectly suited for this task. It observes at infrared wavelengths, where these cold failed stars are more easily spotted, and it can correct atmospheric turbulence with adaptive optics, delivering sharp images like this one. Besides providing invaluable data to understand how brown dwarfs form, the study produced a striking image of “massive stars ‘pushing’ away the clouds of gas and dust around them almost like an animal breaking through its eggshell for the first time,” as do Brito do Vale describes. Who knows, perhaps the cosmic hawk is guarding his baby stars — watching over them as they “hatch”.

Link

Research paper in Astronomy & Astrophysics

Two's company

Mon, 23 Feb 2026 06:00:00 +0100

We humans are strongly influenced by the presence of companions over the course of our lives, shaping each other emotionally, culturally, or intellectually. This shaping effect is made literal in the case of stellar companions, which is the topic of today's Picture of the Week. The pair of points at the centre of the image, taken with ESO’s Very Large Telescope (VLT), are an old stellar couple — a binary system officially called AFGL 4106. As most stars are born in pairs, a big question for astronomers is how does being in a couple impact a star's death?

Before dying, stars expel huge amounts of gas and dust, ingredients for a growing nebula. The massive stars shown here are at close yet distinct late stages of their lifecycles, with one having blown off enough mass to produce a dusty surrounding envelope. In a new paper led by Gabriel Tomassini, a PhD student at the Université Côte d’Azur (France), researchers have mapped this debris, shown here in orange, and precisely characterised the central stars (marked in black).

Imaging astronomical objects close to stars poses a challenge due to the overpowering effect of a star's brightness and, in fact, the stars themselves appear in black as their brightness saturated the detector of the instrument used to make this image. Fortunately, the SPHERE instrument on the VLT is well equipped to deal with large contrasts in light levels, enabling a detailed study of both the high luminosity stars and the faint surrounding nebula for the first time. Moreover, it can correct the blur caused by atmospheric turbulence, delivering very sharp images.

The shape of the nebula reveals the significant impact the companion is having on the gas ejection of the dying star, introducing asymmetries and shifting the clouds of gas and dust away from a perfectly spherical shape. Further observations of star systems like this one allow scientists to better understand how the presence of companions affects the death of stars.

Link

Research paper in Astronomy & Astrophysics

The Milky Way’s glistening band

Mon, 16 Feb 2026 06:00:00 +0100

The setting of today’s Picture of the Week is ESO’s flagship facility: the Paranal Observatory, located in the Chilean Atacama Desert. One of the Auxiliary Telescopes of ESO’s Very Large Telescope is still asleep, with its spherical dome closed. How bad, it misses this wonderful view of the Milky Way!

In ancient times, people weren't too sure what the Milky Way was. They named it after its appearance — a milky band in the night sky. It was Galileo Galilei who first pointed a self-built small telescope at that structure. He realised that the Milky Way was formed of countless stars — a revolutionary discovery!

Our understanding of the Milky Way has advanced considerably: some 100 to 400 billion stars of all ages, masses and colours belong to it. Located in a spiral arm, 25 000 light years away from the centre, is our Sun, making the Milky Way our home galaxy. From this position, we can see the galactic centre very well, as shown in this picture taken by Chilean astrophotographer Alexis Trigo. Large lanes of dark clouds are visible. These dark nebulae block the light from the stars behind them, creating the illusion of fewer stars in that region.

Viewing the glistening band of the Milky Way has been an incredible experience for ages. We have learned a lot about our home galaxy since then, but there is still so much more to uncover. It remains to be seen what revolutionary discoveries ESO’s upcoming Extremely Large Telescope will bring us.

The marvels of Paranal

Mon, 09 Feb 2026 06:00:00 +0100

Today’s Picture of the Week shows the full scope of Paranal’s beauty. Cerro Paranal in Chile’s Atacama Desert, the mountain peak home to ESO’s Very Large Telescope (VLT), is a site of many marvels. And this panoramic image taken by Chilean astrophotographer Alexis Trigo certainly captures them all.

Right in front, one of the movable Auxiliary Telescopes (ATs) stands tall. While this "relatively" small 1.8-m telescope has its eyes shut, its bigger siblings, the Unit Telescopes (UTs), each with an 8.2-m mirror, are scanning the sky. The lasers emerging from the UTs each create a bright artificial star on the sky, so the shifts and swirls of the atmosphere can be measured and corrected to deliver sharp data.

The UT4 telescope, seen here to the right, had been equipped with four lasers for several years already. But in November 2025, when this image was taken, additional lasers were being tested in the other three UTs. These new lasers are part of an upgrade to the VLT Interferometer (VLTI) and its GRAVITY instrument, called GRAVITY+. The four UTs can work together as a huge virtual telescope, and these new lasers will allow them to observe much fainter objects than before.

But the telescopes are not the only marvel that stands out in this picture: the dark sky in the background is just as striking, with the centre of the Milky Way shining to the left. This view is unfortunately polluted by many “scratches” caused by satellite megaconstellations, a growing threat for astronomy that ESO is working hard to mitigate.

The heart of the ELT

Mon, 02 Feb 2026 06:00:00 +0100

Today's Picture of the Week gives an exclusive view into the heart of ESO's Extremely Large Telescope (ELT). While the exterior appears to be almost ready for action, work is ongoing inside to complete the telescope’s structure, illuminated here by the Sun shining through the open, gigantic doors.

This structure is the heart of the ELT and will host the telescope’s mirrors, which will gather the light and send it to the instruments at the sides of the telescope. At the bottom part of the structure, the cell for the main mirror is visible. The tube above connects the main mirror structure with the top ring — the spider structure that holds the secondary mirror crown. Three additional mirrors will be hosted in a tower at the centre of the main mirror, not seen here. Once the light reaches one of the platforms at the side of the telescope, an extra mirror will redirect it to one of the several scientific instruments that will analyse it.

With its 39-metre-diameter, the main mirror will be the largest ever for an optical telescope, making the ELT the biggest eye on the night sky. Consequently, the technical requirements are as extreme as the ELT's name suggests. Everything about this telescope is larger than anything built before, making it the prototype that must perform perfectly, to enable us to explore the universe deeper and sharper than ever before.

Young or old? — There’s both

Mon, 26 Jan 2026 15:00:00 +0100

Today’s Picture of the Week represents an unexpected full circle moment. The depicted object, known as Ve 7–27, was long believed to be a planetary nebula — the end phase of a sun-like star’s life. But ESO’s Very Large Telescope (VLT) has shown that it’s actually a still-forming baby star.

For years the true nature of this nebula had been debated, but the VLT’s MUSE instrument has now captured the first detailed image of this object. It shows that Ve 7-27 is shooting energetic jets with knots or ‘bullets’ along them, which is typical for newborn stars. “Instead of being the “last breath” of a dying star, Ve 7-27 is a newborn one,“ says Janette Suherli, a PhD candidate at the University of Manitoba, Canada and first author of the study that revealed this surprising finding.

But there’s an actual dead star lurking just nearby. The compact yellowish-green smudge to the centre-left of this image hosts a neutron star produced when a massive star exploded as a supernova. This nebula is part of a larger cloud ejected by the explosion, the Vela Junior supernova remnant. The MUSE observations revealed that the baby star Ve 7-27 is embedded in the material expelled by this supernova. The distance to Vela Junior had never been precisely constrained before, but now we know this object is close to Ve 7-27. Since Ve 7-27 is known to be about 4500 light-years away, so is Vela Junior. Pinpointing the distance to Vela Junior means we now finally know its size, how fast it is expanding, how energetic it is, and how long ago the supernova exploded, solving decades of inconsistencies. The discovery therefore gives insights to not only the energetic baby star but also the true nature of Vela Junior and represents an “outstanding case of stellar birth and stellar death co-existing side by side in the same environment,” as Suherli describes.

The precious rings of space

Tue, 20 Jan 2026 09:00:00 +0100

Not all rings are forged in fantasy, my precious! For astronomers, they are found in space. The ones in today’s Picture of the Week are debris discs: the leftovers of planet formation around other stars.

Even our Solar System has a debris disc, known as the Kuiper Belt, where numerous asteroids and comets encircle the Sun beyond Neptune’s orbit. It is believed that the influence of large planets like Neptune prevented the dust and pebbles in this region from clumping together and forming larger bodies. Therefore, debris discs can be seen as remnants of planetary formation, and studying those around other stars is key to understanding the birth of planetary systems.

Using the Atacama Large Millimeter/submillimeter Array (ALMA), a team of astronomers has obtained high-resolution images of 24 debris discs around other stars. The orange images in this Picture of the Week show the distribution of dust in these discs, and the blue ones the distribution of gas in 6 of them.

The origin of gas in debris discs is debated: it could be leftover primordial gas that was present around the star from the beginning, or gas released later on as dust grains collided with each other. The debris disc around the star HD 121617, shown here in the two images at the top-right, is very interesting in this regard. The dust ring (orange) is brighter on one side, indicating a higher concentration of dust grains there. The team found that a vortex of gas could trap dust particles there, but only if the density of gas is very high. Such a high density of gas would be more consistent with this gas being of primordial origin. Further analysis of the full sample of debris discs will tell us more about the secrets of these precious rings.

"I was completely overwhelmed..."

Mon, 12 Jan 2026 06:00:00 +0100

“ ...by the beauty of it all, to the point of forgetting everything around me,” says Julien Looten, a French astrophotographer. During his visit of ESO's Very Large Telescope in Cerro Paranal, Chile, he captured this extraordinary snapshot. Today’s Picture of the Week reveals the astonishing impression he gained of one of the world's darkest skies on Earth.

This 360-degree panorama shows the Milky Way arching above an Auxiliary Telescope of the VLT, with the two Magellanic Clouds next to it. The faint green and red shimmer along the horizon is airglow, light naturally emitted by the atmosphere and only visible under very dark skies. Adding to the scene, one of the Unit Telescopes of the VLT projects laser beams into the sky to correct for blurring caused by atmospheric turbulence. To the left, the zodiacal light can also be seen, stretching like a white brush into the sky.

“Coming from northern France, where the sky is often cloudy and spoiled by light pollution, the contrast upon arriving in Chile was breathtaking: a sky of absolute purity, free from artificial light, with the galactic bulge shining right at the zenith…” Julien says. “ESO gave us a truly unique opportunity, and that night will remain etched in our memory as one of the most beautiful of our lives.”

Survey gives astronomers a latte to think about

Mon, 05 Jan 2026 06:00:00 +0100

Creating a star is hard work, and the process is not very efficient. Current knowledge suggests that a stellar nursery must have a minimum density of gas and dust for a star to form. Only 1-2% of all the gas and dust in these clouds is utilised to ignite a star. But could even denser regions be more efficient at forming stars?

In today's Picture of the Week, we’re looking at GAL316, one of the many stellar nurseries a team of astronomers observed to answer this question. This region is part of a survey called CAFFEINE – an astronomer’s best friend – carried out using the ArTéMiS camera at the Atacama Pathfinder Experiment (APEX), a radio-telescope in the Chajnantor plateau. Now operated by the Max Planck Institute for Radio Astronomy, this telescope captures the faint glow of cold gas clouds, seen here as a blue glow. This glow has been overlaid on a starry background captured with ESO’s VISTA telescope.

Results from the study show that, unlike astronomers, who get more efficient with a bit of caffeine, the densest regions observed with this CAFFEINE survey seemed no more efficient at producing stars than any other stellar nursery above the minimum density.

APEX: the beginning of a new chapter

Mon, 29 Dec 2025 06:00:00 +0100

Today, instead of a picture, we feature a Video of the Week giving a glimpse into one of the highest altitude observatories on Earth: the Atacama Pathfinder Experiment (APEX).

APEX is a telescope designed to explore cold, dark regions of our Universe, such as dense clouds of gas and cosmic dust where new stars are born. While visible light is obscured by the dust, these regions glow bright at the (sub)millimetre wavelengths that APEX observes. APEX allows astronomers, among other things, to study the chemical conditions within these clouds, detecting a variety of molecules in these dark, distant regions of our Universe.

Water vapour in the atmosphere absorbs these wavelengths. That's the reason APEX is located on the Chajnantor plateau in Chile’s Atacama Desert at an altitude of 5100 m: one of the driest regions on Earth with few clouds.

Once a joint project of the Max-Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO) and ESO, APEX now enters a new chapter and becomes a project solely of the MPIfR. But the science continues!

This caption was written by Julian Seeholzer, one of the winners of the European Contest for Young Scientists in 2023.

Happiest of holidays from ESO! (2025)

Mon, 22 Dec 2025 06:00:00 +0100

2025 — another exciting year — comes to an end. With all the groundbreaking discoveries made, milestones achieved and beautiful pictures captured, we can look back at yet another successful year. At the same time, we excitedly look ahead for the next year to come. Our 2026 new year's resolutions are clear: continue to advance innovation, set our ambitions high and safeguard our dark and quiet skies! Let us therefore enter the new year with purpose, unity and vision. We look forward to a great year! Until then, it is time to relax and enjoy! We wish you restful holidays with your family and friends and a happy new year!

Young stars blow bubbles?

Fri, 19 Dec 2025 17:00:00 +0100

We know that a star’s childhood is turbulent: growing via a disc of gas and dust, the same disc from which planets form. Young stars also experience outbursts, expelling material via fast jets that regulate how much material is left to feed the young stars and form planets around it. Today’s Picture of the Week shows one of those jets interacting with the surrounding material.

The background image, taken with the NASA/ESA Hubble Space Telescope, shows the young star SVS 13, located in the star-forming region NGC 1333 about 1000 light-years away. This star is expelling gas in the form of clumps known as “molecular bullets”. The insets show observations of one of those “bullets” taken with the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner. Each frame displays gas moving at different speeds, ranging from 35 km/s (red) to 97 km/s (blue).

This series of images is similar to a medical tomography, and allows astronomers to reconstruct the 3D shape of the rings and shells of gas that the jet creates as it interacts with its environment. “This is the first time such a degree of fine detail has been reached, thanks to the exquisite sensitivity achieved in our study with ALMA,” said Guillermo Blazquez-Calero, lead author of the study recently published in Nature Astronomy. This will help astronomers understand the not-so-peaceful infancy of stars and how planets form around them.

Link

Research paper in Nature Astronomy

Endless expanse

Mon, 08 Dec 2025 06:00:00 +0100

This view of the seemingly endless expanses of the Chilean Atacama Desert is definitely worth to be today’s Picture of the Week. The silver full Moon shines bright in the beautiful gradient evening sky. Below it, to the right, the giant dome of ESO’s Extremely Large Telescope (ELT) glows with the golden sunset light.

The ELT is perched atop Cerro Armazones, at an altitude of 3046 m. The dome might look small in the image, but the full 30-minute walk via the set of stairs from the entrance of the dome to its top, indicates its gigantic size: 80 m high and 93 m wide. Weighing about 6100 tonnes, the dome is designed to protect the telescope and its mirrors, including the 39-m wide primary mirror — the biggest eye on the sky.

To the left of Cerro Armazones the last sunbeams of the evening cast a dark triangular shadow: Cerro Paranal, home to ESO’s Very Large Telescope (VLT), from where this picture was taken by Luca Sbordone, ESO staff astronomer. It’s no wonder that this site hosts so many professional telescopes, as it boasts the darkest skies on Earth. Chile is in fact home to all of ESO’s observatories, thanks to a long-lasting partnership that goes back more than 60 years — may it be as timeless and inspiring as this view.

In preparation for the dark night

Mon, 01 Dec 2025 06:00:00 +0100

Before the night emerges, ESO’s Paranal Observatory glows in the colourful light of the Chilean sunset. Today’s Picture of the Week was taken by French photographer Julien Looten, who captured the Very Large Telescope (VLT) right as the Sun set, creating a pinkish band — the Venus belt.

The Venus belt, unlike the name suggests, is not related to the planet Venus. It is an atmospheric phenomenon caused by the scattering of the Sun’s light when it either rises or sets, visible on the opposite side of the sky. As sunlight reaches the far end of the atmosphere, small particles scatter it back towards the observer, creating a pinkish band. The dark band right below it is the shadow of the Earth cast on to the sky as the Sun sinks below the horizon on the opposite side.

Looten caught this moment in a panorama right after sunset, before the arrival of the night when “the excitement was at its peak”, he explains. The same way the photographer prepared to capture the clearest night skies above the Chilean Atacama Desert, the telescopes of the Paranal Observatory got ready to observe the mysteries of the cosmos.

A telescope fist bump in the sky

Tue, 25 Nov 2025 09:00:00 +0100

Only by working together as a team can all of ESO’s 8 m telescopes become the Very Large Telescope Interferometer (VLTI) — and today’s Picture of the Week captures this teamwork perfectly. The photograph, taken by Juan Beltrán, an instrumentation technician at ESO’s Paranal Observatory in Chile, marks the beginning of a new interferometry era.

Most of the time these so-called Unit Telecopes (UTs) work as standalone telescopes, each one observing a different object. But they can also point at the same target, combining their light with interferometry to obtain the same level of detail of a huge 130 m virtual telescope. This requires measuring and correcting the effects of Earth’s atmosphere, which was previously done through bright reference stars, hard to find next to the object one wants to study.

As part of the GRAVITY+ upgrade, new lasers were installed in the previously unequipped UTs. These lasers create artificial stars high up in the atmosphere, near the observation target on sky, that can be used to correct atmospheric turbulence. Now that the lasers are ready, the observations are not limited to natural bright reference stars anymore, opening the whole southern sky to the VLTI. And the GRAVITY+ trial run in early November blessed us with the mesmerising view of all four lasers pointing to one target on the sky, as if they were fist bumping as a team.

Link

Timelapse of the GRAVITY+ lasers

A hypnotising view of Paranal

Mon, 17 Nov 2025 06:00:00 +0100

“I couldn't believe I was photographing a circumpolar startrail in Paranal; without a doubt, one of the most incredible experiences I've had as a photographer,” says Osvaldo Castillo, the Chilean astrophotographer responsible for this stunning Picture of the Week.

This circular motion of the stars is caused by the rotation of the Earth around its axis. The point at which Earth's rotation axis extends to in the sky is called a celestial pole, which in today's image is the centre around which all these stars seem to move or trail — hence, the name circumpolar startrail.

Osvaldo was able to capture this hypnotising motion at ESO’s Paranal Observatory in Chile. With the tip of one of the Auxiliary Telescopes almost perfectly aligning with the southern celestial pole, it seems as if the sky revolves around the telescope, making it the centre of attention.

But capturing these circular startrails is no easy task. Multiple images must be taken over several hours with a long exposure time — a slight misalignment can completely ruin the outcome, as the final trails are only visible when the individual images come together. And since the telescope moves as it points to different locations, different shots need to be taken for the foreground and background. Osvaldo explains that he took “almost 300 images and you can't see the result immediately. Fortunately, the calculation and orientation to the South were accurate." Lucky for us! We now get to enjoy this mesmerizing Picture of the Week.

A dance of two pairs

Mon, 10 Nov 2025 06:00:00 +0100

While the two largest satellite galaxies of the Milky Way — the Magellanic Clouds — shine upon the Chilean Desert, two Auxiliary Telescopes that feed light into ESO’s Very Large Telescope Interferometer (VLTI) point up to the sky, unravelling the mysteries of the cosmos. In today’s Picture of the Week, French photographer Julien Looten wanted to capture the interplay of cosmic and technological pairs.

The Magellanic Clouds are two dwarf galaxies that accompany our Milky Way through the cosmos. Indigenous cultures in the southern hemisphere often named them after water wells. At the same time the Auxiliary Telescopes are somewhat companions of the larger VLT’s Unit Telescopes, exploring the vastness of the universe. In the background we see the extremely faint but colourful airglow of Earth's atmosphere.

All together this image shows the “immensity of the cosmos”, as Looten explains, in contrast to the human silhouette on the right side of the picture. It reminds us of how small we are as humans compared to the sizes of cosmic objects and the telescopes we observe them with. While we have the ability to study the greatness of the universe, our passage on Earth is fleeting — sometimes all we can or should do is watch and admire.

Open Sesame: The ELT doors move for the first time

Mon, 03 Nov 2025 06:00:00 +0100

As the construction of ESO’s Extremely Large Telescope (ELT) continuously develops, its performance needs to be secured at every step. Today’s Picture of the Week is a timelapse of an important milestone: the first movement of one of the dome’s giant doors.

The ELT dome and its doors guard the telescope from the harsh conditions of the Atacama Desert in Chile. Each of the doors will weigh approximately 650 tonnes once completed, including walkways, ducts for heating, ventilation and air conditioning, and other related mechanisms already installed. Moving these massive doors is no small feat, and the test shown in this timelapse, captured in early October, is key to ensuring that everything works as it should.

Once both doors are fully installed and operational they will be closed, providing a more stable and controlled environment inside the dome for the upcoming construction phases. These include installing critical systems like the hydrostatic oil bearings that will allow for a smooth and precise movement of the telescope. Once the ELT is in operation the doors must respond quickly to protect the telescope against sudden changes in the external conditions. At night, the doors will allow the biggest eye on the sky to scrutinise Chile’s uniquely dark skies.

The magic of a pristine sky

Mon, 27 Oct 2025 06:00:00 +0100

Today's Picture of the Week portrays the Milky Way arching over ESO's Very Large Telescope (VLT). Indulged in memories, the French astrophotographer Julien Looten, who capture this image, explains: “this picture has symbolic value for me, as it marked the closing of the night.”

Three of the four VLT Unit Telescopes are centred under the Milky Way, while the fourth is hidden on the right side of the image. The smaller telescope in the background, to the right, is the VLT Survey Telescope (VST).

The sky appears split in two: a greenish haze on the left side and a reddish one on the right. This so-called airglow is caused by chemical processes in the upper layers of Earth's atmosphere. Depending on the type of atoms or molecules excited, the glow can exhibit different colours.

Airglow is extremely faint and only noticeable in the darkest regions on Earth, such as the Chilean Atacama Desert, where the VLT is located. Artificial lights from even distant sources greatly outshine the faint airglow. Preserving these pristine skies is not only key to enable cutting-edge research, but also to allow more people to experience the magic of a perfectly dark night, like Julien Looten did with this image.

A pink speckle in the southern sky

Mon, 20 Oct 2025 06:00:00 +0200

Today’s Picture of the Week showcases the mesmerising dark sky above ESO’s Paranal Observatory in Chile. The sky in the southern hemisphere is home to unique jewels like the Magellanic Clouds and one particularly special eye-catcher in this image: the Carina Nebula.

The Carina Nebula — a massive star-forming region — is visible here as a big pink spot right above one of the four Auxiliary Telescopes of ESO’s Very Large Telescope (VLT). This sight was a unique one for the French photographer Julien Looten, who captured the image. “It was an unforgettable moment,“ he said about finally seeing the Carina Nebula with his own eyes, as such a view is not possible from the northern hemisphere. But Paranal’s location in the southern hemisphere and its uniquely dark skies make it possible to capture this breathtaking view.

This nebula is home to Eta Carinae, a pair of massive short-lived stars that are shedding off large amounts of material. The structure of this cloud has been studied in detail with the VLT Interferometer, by linking together three Auxiliary Telescopes like the one in this image to create a huge “virtual” telescope. The catastrophic demise of Eta Carinae contrasts with the quiet of the Atacama Desert, all nicely coming together in harmony in this beautiful picture of the southern sky.

Picture of The Week

ESO’s Extremely Large Telescope from space

An ExTrA sphere

The Triangulum galaxy up close

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Reaching for the stars

New look at the stars around the Milky Way's centre

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A cosmic hawk and its baby stars

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Two's company

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The Milky Way’s glistening band

The marvels of Paranal

The heart of the ELT

Young or old? — There’s both

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The precious rings of space

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"I was completely overwhelmed..."

Survey gives astronomers a latte to think about

APEX: the beginning of a new chapter

Happiest of holidays from ESO! (2025)

Young stars blow bubbles?

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Endless expanse

In preparation for the dark night

A telescope fist bump in the sky

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A hypnotising view of Paranal

A dance of two pairs

Open Sesame: The ELT doors move for the first time

The magic of a pristine sky

A pink speckle in the southern sky