Picture of the Week

8 July 2019: This red-hued cloud of gas is named Abell 24, and is located in the constellation of Canis Minor (The Lesser Dog). It is something known as a planetary nebula — a burst of gas and dust created when a star dies and throws its outer layers into space. Despite the name, planetary nebulae have nothing to do with planets. The term was coined by William Herschel, who also famously discovered Uranus; in a time of low-resolution astronomy, these nebulous objects appeared to resemble giant planets swimming in a dark cosmos. A Sun-like star spends most of its life converting hydrogen into helium in its core. In its twilight years the star runs out of fuel and becomes unbalanced; it can no longer resist the inward crush of gravity and the core begins to collapse. The temperature in the core rises dramatically while the cooler outer layers expand, causing the entire ...

1 July 2019: Almost exactly 100 years ago, a remarkable event occurred: a total solar eclipse. This eclipse was special in more ways than one. Firstly, at just under seven minutes in duration, it was the longest such eclipse in over 500 years. Secondly, it was used by astronomers to explore the then-new theory of general relativity — with successful and groundbreaking results. Einstein published his general theory of relativity in 1915. The total solar eclipse of 1919 offered the perfect opportunity to test it experimentally, by exploring whether — and how — the immense gravity of the Sun bends and distorts incoming light from more distant stars, as predicted by Einstein’s theory. For a brief moment during the eclipse, the Moon would block the Sun’s light in the sky and make visible some of the stars that lie close to the line of sight of the Sun, not normally visible during the ...

24 June 2019: ESO’s observatories located on the mountains of Chile — La Silla, Paranal and Chajnantor Plateau — are home to a wide range of telescopes built and operated by the organisation’s 16 Member States. As time passes, older telescopes are slowly overtaken by their newer and more advanced peers. One of these old-timers is pictured here: the Swedish-ESO Submillimetre Telescope (SEST). Built back in 1987 at La Silla, the SEST was a groundbreaking instrument. It was the only large telescope in the southern hemisphere to study radio waves from objects in the distant Universe (known as submillimetre astronomy). A huge dish, with a diameter of 15 metres, the telescope was able to observe some of the most extreme phenomena in the cosmos. Eventually, however, newer and more advanced telescopes — such as the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Pathfinder Experiment (APEX), both situated on Chajnantor Plateau — began to ...

17 June 2019: This stunning photograph shows some of the antennas comprising the Atacama Large Millimeter/submillimeter Array (ALMA), all observing a panoramic view of the Milky Way’s centre. There is far more to ALMA than shown here; the array can span distances of up to 16 kilometres and is formed of 66 individual antennas! Some features visible in the sky include Crux (The Southern Cross) just above and to the right of the nearest antenna, and the Carina Nebula slightly further to the right. Astronomers use ALMA to peer into gigantic star-forming molecular clouds, and to observe galaxies forming at the very edge of the observable Universe. The green lights visible on the telescopes are a normal part of their operation, but in this scene they also cast an ethereal, otherworldly glow over the Chilean site. This photograph was taken by Petr Horálek, one of our ESO Photo Ambassadors.

10 June 2019: This rugged, wrinkled landscape may resemble Mars, but it is in fact much closer to home — this patch of rippled terrain is a northern region of the Chilean Atacama Desert, home to many of ESO’s world-leading telescopes and observatories. The distinctly otherworldly appearance of the desert has not gone unnoticed; this part of the world is actually used as an “analogue site” for Mars! Scientists visit the Atacama to explore: soil composition and texture; potential similarities in surface geology and features; limitations for past biological activity (including whether such locations may, or may once have been, friendly to extremophile life); weather conditions; aridity and more. Perhaps most importantly, sites like the Atacama can help us to prepare for both in-progress and planned space missions (manned and unmanned alike) by providing a suitable environment in which to test equipment, manoeuvres, and mission plans. Visible just below right of centre in ...

3 June 2019: This stunning long-exposure photograph by ESO Photo Ambassador Petr Horálek captures the hive of activity that is ESO’s La Silla Observatory, the distant glow of roads and settlements in the Chilean Atacama Desert, and the unmissable faint green radiance of airglow (produced by light in Earth’s upper atmosphere). Flirting with the horizon, the mythical Seven Sisters of the Pleiades open star cluster can be seen dancing above distant mountain peaks. Directly above them, the dazzling constellation of Orion (The Hunter) dominates the view, as giant clouds and arcs of ionised gas — called emission nebulae, and seen here as red patches — encompass the imagined form of mythological hunter. The familiar sight of the Milky Way is also visible, carving its way across the night sky. The La Silla Observatory is located in northern Chile at an altitude of 2400 metres. It enjoys some of the darkest night skies on ...

27 May 2019: Even in their downtime, many astronomers cannot resist catching one more glimpse of the star-studded sky. This image captures a fascinated astronomer stargazing from the Residencia, ESO’s living quarters for staff working at Paranal Observatory in Chile. This view shows the dusty and star-filled band of the Milky Way rising over the Atacama Desert, the remote home of ESO’s Very Large Telescope (which sits atop Cerro Paranal). The desert’s inhospitable conditions drove the construction of the Residencia, which was completed in 2002. An oasis for astronomers, the building contains 108 bedrooms built into a depression in the desert, and is considered a refuge from the harsh conditions of the Atacama — it even hosts a verdant garden and swimming pool! The building was designed to blend into its environment, and to minimise light pollution in the exceptionally dark skies of Paranal. The Residencia’s fascinating and unusual setting captured the eye ...

20 May 2019: In a once-in-a-lifetime opportunity, staff at ESO’s Paranal Observatory were treated to a unique performance by the world-renowned cellist Yo-Yo Ma. On 1 May 2019, the celebrated musician visited Paranal to see the astronomical centre, home of the Very Large Telescope (VLT), and experience its dazzling skies first-hand. To the delight of the staff, he gave a special concert for which he requested completely dark skies. He is pictured here during the starlit performance, with the majestic band of the Milky Way and the Magellanic clouds overhead, making for a uniquely atmospheric setting. He gave renditions of several Bach cello suites among other pieces, and even asked his audience if they had any special requests. The next day, Yo-Yo Ma met with some members of staff, who shared their experiences of working in the extreme environment of the Atacama Desert to unveil the mysteries of the Universe. He was given ...

13 May 2019: The constellation of Orion (The Hunter) is one of the most recognisable collections of stars in the night sky. We have noted Orion’s prominent stars for tens of thousands of years at least, and likely far longer. Chinese astronomers called it 参宿 or Shēn, literally “three stars”, for its three bright dots (which form the Hunter’s belt). The ancient Egyptians regarded it as the gods Sah and Sopdet, manifestations of Osiris and Isis, respectively, whereas Greek astronomers saw a brave hunter — the eponymous Orion — with his sword above his head, ready to strike. Mythology aside, Orion is a fascinating patch of sky. This image, from ESO's Very Large Telescope, shows a reflection nebula nestled at the heart of the constellation — NGC 2023. Located close to the well-known Horsehead and Flame Nebulae, NGC 2023 lurks about 1500 light-years away from Earth, and is one of the largest reflection ...

6 May 2019: This striking UHD panorama shows a bizarre-looking scene at ESO’s Paranal Observatory, home to ESO’s Very Large Telescope (VLT). The Milky Way graces the skies above the observing site every single night, and is visible in stunning detail and clarity. But here, the galaxy appears to dip down through the night sky and create two separate columns, while still filling the sky towards the top of the frame. Why is this view so distorted? The sculpting and reshaping of this familiar celestial scene result from the way in which the photographer, ESO Photo Ambassador Petr Horálek, captured the image. Horálek photographed the entire dome of the sky, from zenith to horizon, a full 360 degrees around. The “two Milky Ways” are in fact a single band — the plane of our galaxy as it arcs across the sky from horizon to horizon. As it passes overhead, it appears to spread ...

29 April 2019: This is one of 74 nearby galaxies whose stellar nurseries were recently observed by the Atacama Large Millimeter/submillimeter Array, or ALMA, in an astronomical census called Physics at High Angular resolution in Nearby GalaxieS (PHANGS). So far, around 100 000 of these stellar nurseries have been imaged in over 750 hours of observation. ALMA’s remarkable sensitivity provides data at high enough resolution to study these regions in detail, and shows that some are bursting with new stars, while others evolve more gradually. This anticipated diversity in the process of how stars form was the motivation behind this enormous effort. There have long been theories that aimed to explain how and why these differences might occur, some involving the characteristics of the home galaxy itself — properties such as size, age, and internal dynamics — but our lack of high-resolution data had been an obstacle to testing them. The vast quantity ...

22 April 2019: This ESO Picture of the Week, captured by ESO Photo Ambassador Petr Horálek, shows a bright crescent Moon hanging above the Chilean Andes, embedded in a blood-red sky that floods the frame with waves of deep crimson. Also seen here are a couple of the antennas belonging to the Atacama Large Millimeter/submillimeter Array (ALMA), a state-of-the-art observatory that studies light from some of the coldest objects in the Universe. The silhouetted duo of antennas are seen peering upwards, eager to begin their evening of stargazing — and impatient for the eye-catching ripples of cloud to clear. At an altitude of 5000 metres in the arid Atacama Desert, clouds like these are relatively uncommon. The atmosphere in this region of northern Chile is incredibly dry and regularly leads to clear skies, offering around 300 cloudless nights per year! ALMA has 66 individual constituent antennas, each of which can be moved very ...

15 April 2019: This sweeping panorama was captured under tough conditions. ESO’s Very Large Telescope (VLT) is one of the most advanced observatories in the world, gathering astronomical data of unsurpassable clarity from Cerro Paranal, an isolated site atop a lonely mountain in the Chilean Atacama Desert. This far-flung corner of the globe has many benefits; it offers some of the driest and clearest observing conditions on Earth — some of the weather stations in the Atacama Desert have never recorded rainfall! — and a total lack of light pollution. Paranal’s stargazers can see a sky full of stars even before sunset, while the sinking Sun illuminates ground frost and casts an ethereal and irreplicable glow across the entire observatory. This isolation also has its downsides. Reaching the remote site takes dedication. There is no public transport to Paranal, so visitors must travel by car from Antofagasta airport in the north, or 110 ...

8 April 2019: The four large Unit Telescopes comprising ESO’s Very Large Telescope sit quietly beneath a purple and gold sky, calmly basking in the last rays of sunlight over Cerro Paranal in the Atacama Desert, northern Chile. The tiny crescent Moon can just about be seen at the centre of the frame — the Moon looks “upside down” from here, its familiar crescent shape apparently inverted. This is normal for the southern hemisphere as a result of the path the Moon takes through the night sky, and the perspective from which the observer is viewing it. This appearance is also known as a “wet Moon” or “Cheshire Moon”, as the tips of the crescent curve upwards to represent either a bowl — which was believed to slowly fill with rain in Hawaiian mythology — or the wide smile of Lewis Carroll’s Cheshire Cat from Alice’s Adventures in Wonderland. This photo was taken ...

1 April 2019: As dusk falls, lampposts gently illuminate the curves and angles of the ESO Supernova Planetarium & Visitor Centre. Treetops are silhouetted against the fading red glow stretching along the horizon, while artificial lights cast bright pools and carve out shadowy corners, creating an atmospheric setting around ESO’s Headquarters in Garching, Germany. The diagonal line of bright dots streaking across the sky shows the planet Mercury, which was named after the Roman messenger god. Its path is captured in multiple exposures: about 60 images taken over the course of an hour. Mercury is normally a very difficult planet to observe, largely owing to its proximity to the Sun, whose brightness easily obscures it. Seeing it from a city is especially difficult owing to light pollution. However, on this occasion, several factors conspired to allow ESO photo ambassador Petr Horálek to capture these shots: the night was especially clear; it was just ...

25 March 2019: This astonishing image clearly illustrates why astronomical observatories are usually built in remote, and often inhospitable, places. At ESO’s La Silla Observatory in Chile, the sky is so clear and untroubled by man-made sources of light that it appears as if a brightly-coloured celestial firework display is in progress! This photograph, taken by ESO Photo Ambassador Petr Horálek, has been digitally projected to show as much of the sky as possible. This is why the roads leading to ESO’s 3.58-metre New Technology Telescope (left) and 3.6-metre telescope (right) appear distorted, and the bright river of light that is the Milky Way seems to curve across the sky, stretching from horizon to horizon. Cosmic fireworks aside, this scene is filled with awe-inspiring phenomena. The pink “fireworks” themselves are actually large accumulations of glowing gas known as nebulae. To the right of the Milky Way lie the Magellanic Clouds, two nearby dwarf ...

18 March 2019: It’s impossible to miss the star in this ESO Picture of the Week — beaming proudly from the centre of the frame is the massive multiple star system Tau Canis Majoris, the brightest member of the Tau Canis Majoris Cluster (NGC 2362) in the eponymous constellation of Canis Major (The Great Dog). Tau Canis Majoris aside, the cluster is populated by many young and less attention-seeking stars that are only four or five million years old, all just beginning their cosmic lifetimes. The Tau Canis Majoris Cluster is an open cluster — a group of stars born from the same molecular cloud. This means that all of the cluster’s inhabitants share a common chemical composition and are loosely bound together by gravity. Having been born together, they make an ideal stellar laboratory to test theories of stellar evolution, the chain of events that leads from a star’s birth in a ...

11 March 2019: On the night of 20 January 2019 Coquimbo, Chile shook with the force of a magnitude 6.7 earthquake. Although Coquimbo lies 90 kilometres from ESO’s La Silla Observatory, its effects were far from unnoticed. This unique image shows the earthquake as recorded by the Rapid Action Telescope for Transient Objects (TAROT), a telescope designed to monitor gamma-ray bursts. On the night in question, TAROT was imaging geostationary satellites, which look like static points in the sky as seen from a telescope on the ground. As a result, the stars are recorded as trails, as the Earth rotates on its axis during the exposure. In this picture, three 10 second images, taken in rapid succession on the night of the earthquake, have been overlaid. The first image (left) was started 41 seconds after the start of the earthquake, and the last (right) finishes about 100 seconds after the beginning of the ...

4 March 2019: If you had a brand new state-of-the-art telescope facility, what would you look at first? Researchers at the SPECULOOS Southern Observatory — which comprises four small telescopes, each with a 1-metre primary mirror — chose to view the Lagoon Nebula. This magnificent picture is the result, and is one of the SPECULOOS’ first ever observations. The nebula is a cloud of dust and gas in our galaxy where new stars are being born, and is found roughly 5000 light-years from us. This striking image is made even more impressive by the fact that the SPECULOOS isn’t actually designed to study nebulae. The name says it all — SPECULOOS, the Search for habitable Planets EClipsing ULtra-cOOl Stars. In other words, the primary mission of this telescope facility is to find Earth-like planets orbiting faint nearby stars. The candidates it discovers will be passed over to larger telescopes, such as ESO’s forthcoming ...

25 February 2019: This Picture of the Week is a special treat: a first-light image from the newest resident of ESO’s Paranal Observatory, the SPECULOOS Southern Observatory. This planet-hunting machine aims to observe nearby but dim stars to locate exoplanets for other telescopes — such as ESO’s forthcoming Extremely Large Telescope (ELT) — to study in detail. Comprising four one-metre telescopes, each named after one of Jupiter’s Galilean moons, SPECULOOS promises to open up new frontiers in exoplanet research. This image, however, is obviously not of a faint star, but of a galaxy called NGC 6902. Before a telescope starts its primary mission it must successfully undertake an event called “first light”: the first time it is used for a scientific observation. Astronomers typically pick well-known objects for this initial test of a telescope’s capabilities, which is half demonstration and half celebration. In this case, the team settled on NGC 6902 as the ...