Picture of the Week

5 July 2021: Cerro Armazones is the home of ESO’s upcoming flagship facility, the Extremely Large Telescope (ELT). Located in the Chilean Atacama Desert and just 20 km away from ESO’s Paranal Observatory, home to the Very Large Telescope, Cerro Armazones sits just over 3000 metres above sea level. The isolated nature of this peak is illustrated by a magnificently clear band of the Milky Way galaxy that frames the Armazones crater almost perfectly. This isolation, away from the light pollution of cities, makes the Atacama Desert an ideal location for astronomical facilities, including the ELT, which is set to be “the world’s biggest eye on the sky”. This image, taken on 5 July 2019, shows the excavated mountaintop, currently a construction site. The pouring of concrete for the foundation began in December 2019, and the construction of this epic telescope is expected to be finished later this decade.

28 June 2021: A spectacular lunar halo — known as a 22° halo — formed in the sky above ESO’s La Silla Observatory. The optical phenomenon is a result of moonlight interacting with millions of ice crystals suspended in the atmosphere, forming a ring with an apparent radius of approximately 22° around the moon. It is also known as the “moon ring” or “winter halo”. While this is a beautiful sight, it creates conditions which are not optimal for astronomical observations. Clouds and the bright light of the moon affect the quality and accuracy of astronomical observations. However, that does not diminish the allure of this ethereal sight, and in fact some stars remain visible. Notably, Sirius, the brightest star in the night sky, can be seen at the top edge of the image, just left of the centre.

21 June 2021: Perched between the cascading arch of the Milky Way and the dark mountainside of La Silla Observatory lies the New Technology Telescope (NTT). Since 1989 this ESO telescope has observed and taken images of our night sky in exquisite detail. Some of its more recent achievements include: the observation of the merging of two neutron stars; a more detailed insight into the structure of asteroids; the analysis of hundreds of planetary nebulae; and even research into planets in far off solar systems. Telescopes with larger primary mirrors are able to capture more light. However, a larger mirror’s perfect shape is more difficult to maintain. Astronomers found that with primary mirrors over five metres in diameter, image quality decreased enormously as gravity pulled them out of shape (NTT is 3.5 meters in diameter and was meant as a pioneer project to allow telescopes with larger mirrors to be built). Active optics, ...

14 June 2021: The dark skies above ESO’s Paranal Observatory, home to ESO’s Very Large Telescope (VLT), yield breathtaking views so clear and so full of stars that you could almost touch them. Standing atop a platform at VLT, ESO Photo Ambassador Petr Horálek reaches towards a standout object in the sky. You may assume this bright body, like many others in the sky, to be a star, but it is in fact a planet in our Solar System: the gas giant Jupiter. Closer to Earth, the four Unit Telescopes (UTs) that comprise the VLT can be seen in the background. Each UT features an 8.2-metre mirror and they operate synergistically to produce some of the sharpest views of the Universe. Accompanying the four UTs are four smaller, moveable Auxiliary Telescopes (ATs) which have 1.8-metre mirrors. The Chilean Atacama desert once again proves its value as the ideal location for ESO’s VLT. ...

7 June 2021: This ESO Picture of the Week features a galaxy named both NGC 4254 and Messier 99, a beautiful cosmic spectacle located in the constellation of Coma Berenices (Berenice’s Hair). Messier 99 is special, owing to its classification as a grand design spiral galaxy: a kind of galactic architecture featuring strong, prominent, well-defined arms that wrap clearly around the galaxy’s centre. Only around 10 percent of all spirals are of the grand design variety, making objects like Messier 99 somewhat uncommon. The justification behind Messier 99’s categorisation is clear in this image; bright, swirling arms carve through the dark surrounding space, and are easily identifiable as a number of different, coherent structures. This image was created as part of the ESO Cosmic Gems programme, an outreach initiative to produce images of interesting, intriguing or visually attractive objects using ESO telescopes, for the purposes of education and public outreach. The programme makes ...

31 May 2021: If you look closely at the faint and fuzzy centre of this picture, you will find a ghostly galaxy — the not-so-spooky-sounding UDG4 — captured using ESO’s VLT Survey Telescope (VST). UDG stands for ultra-diffuse galaxy: objects as large as the Milky Way but with 100 – 1000 times fewer stars. These galaxies are extremely faint and lack star-forming gas, which makes them appear almost like a fluffy cosmic cloud, or a smudge in space. Their origins remain uncertain, but astronomers speculate that they could be “failed” galaxies that lost their gas supply early in their lifetimes. This image of UDG4 was taken as part of a study from a much larger program, the VST Early-type Galaxy Survey (VEGAS), which aims to investigate very faint structures in galaxy clusters — large groups of many galaxies bound together by gravity. The study, led by Enrichetta Iodice from the Istituto Nazionale di ...

24 May 2021: In this image, the first rays of the morning Sun shine down upon Cerro Paranal in northern Chile, the home of ESO's Very Large Telescope (VLT) — signalling that another successful night of observations has concluded at the world’s most productive ground-based astronomical facility. Rising 2635 metres above sea level, the VLT’s site is amongst the best in the world for gazing deep into the Universe. Giving a sense of the site’s altitude is the apparent “sea” in the background. This is, however, a trick of the eye; the Atacama Desert, where ESO’s VLT is located, is a very dry place. Rather than liquid water, the distant, blue-hued sea is instead composed of clouds that form at lower elevations. Link: Panoramic image of the VLT

17 May 2021: ESO's La Silla Observatory stretches out before your eyes in this image taken by ESO Photo Ambassador Gerhard Hüdepohl. This perspective looks down from a mountaintop in the Chilean Atacama Desert, capturing numerous telescopes and support buildings winding through the barren, remote landscape. The telescope sitting proudly in the foreground is the ESO 3.6-metre telescope, with its curved white dome and grey base. A small bridge connects the telescope to a similarly white-domed, skinnier cylinder — the now-decommissioned ESO Coudé’ Auxiliary Telescope. In the distant background, a series of low, rectangular buildings can be seen sprawling across the mountainside; these include the site’s operations centre, dormitories, and a hotel. As this image attests, no other signs of human civilisation exist for many kilometres around. Sitting at a challenging altitude of 2400 metres and on the outskirts of the driest desert on the planet, La Silla has little chance of becoming ...

10 May 2021: This week’s picture of the week features DG121, an HII region — a cloud of ionised hydrogen — located in the constellation of Puppis (the Stern). HII regions, a type of emission nebulae, are created when young, massive stars release enough ultraviolet energy to ionise the surrounding gas clouds. These regions tend to have irregular structures and lack sharp boundaries, giving them their hazy, yet photogenic, appearance. The brightest star in the DG121 region, seen near the centre in this picture, is HD 60068. This spectacular image was taken with the FORS 2 (FOcal Reducer and low dispersion Spectrograph 2) instrument on ESO’s Very Large Telescope in the Chilean Atacama Desert. This instrument has been described by astronomers as "the Swiss army knife of instruments at Paranal", because of its ability to study many different astronomical objects in many different ways.

3 May 2021: This Picture of the Week appears to show a lone antenna gazing at the sky — but in reality this antenna is far from lonely. It is part of the Atacama Large Millimeter/submillimeter Array (ALMA), a telescope that comprises 66 high-precision antennas spread out across the Chajnantor plateau, located high up in the Chilean Andes. In this image we are treated to a spectacularly multi-coloured view of the sky above ALMA: green airglow hovers above the horizon, the Large Magellanic Cloud peeks out from behind the antenna, and the magnificent sprawl of the Milky Way stretches out overhead. These antennas are optimised to collect light at millimetre wavelengths, between infrared and radio waves, giving ALMA a view of the Universe that is very different to our own. Human eyes have evolved to see visible light while ALMA views the cosmos at longer wavelengths, picking up light from some of the ...

26 April 2021: Do you ever get the feeling that you're being watched? This friendly-looking object is the result of two galaxies merging into one another, complete with a pair of eyes hiding two growing supermassive black holes and a swirling grin. Such mergers are rare in our galactic neighbourhood; Mrk 739 is close enough (astronomically speaking) to study the event in detail, and thus gain a better understanding of the dramatic processes that take place during these cosmic mergers. By using the MUSE instrument on ESO’s Very Large Telescope, the team of astronomers, led by master’s student Dusán Tubín at the Pontificia Universidad Católica de Chile, were able to study the effects of both the merger and the radiation emitted by the growing gigantic black holes. Their study answers questions about the motion of the galaxies, the age of their stars, and the elements they are made up of. They have found ...

19 April 2021: This panoramic selfie was taken on 9 April 2016 by ESO Photo Ambassador Petr Horálek. Petr was in the Chilean Atacama Desert as a member of ESO’s Fulldome Expedition team, a select group of photographers who captured an array of stunning, ultra-high-definition visuals for use primarily in the ESO Supernova Planetarium & Visitor Centre. The landscape looms large around photographer Petr in this image, making him appear small beneath the striking Chilean sky. He can be seen standing just beneath a column of zodiacal light — perfect positioning that makes this image appear even more otherworldly. The wide, round-topped objects visible here are some of the 12-metre antennas comprising the Atacama Large Millimeter/submillimeter Array (ALMA). ALMA is the largest ground-based astronomical observatory in the world, and is located on the Chajnantor Plateau in Chile at an altitude of 5000 metres. A total of 66 antennas make up the array, and ...

12 April 2021: Great care is taken to ensure that the site for a new telescope will provide the best possible observing conditions. This picture of the week was captured in 2019 by ESO photo ambassador Petr Horálek from the top of Cerro Armazones, Chile, where the Extremely Large Telescope (ELT) is being constructed. Situated in the heart of the Atacama desert, at an altitude of 3046 metres, this high and dry location will be vital to showcase and utilise the ELT’s incredible observational power. This extraordinary panorama of the Atacama desert frames a sprawling view of our own Milky Way galaxy, seen with stunning clarity as a result of the minimum light pollution in this remote area. Massive interstellar dust clouds obscure the more distant starlight, leading to the distinctive “mottled” band in the night sky.

5 April 2021: The Atacama Desert in Chile is one of the darkest and most peaceful astronomical sites on Earth — and has, as a result, proven to be the perfect location for ESO’s various observatories and powerful instruments. This view shows ESO’s Paranal Observatory, home to the behemoth Very Large Telescope (VLT). The constituent telescopes of the VLT can be seen standing sentinel beneath a star-studded sky featuring the glittering arch of our Galaxy, and the glowing Magellanic Clouds (left). As this image demonstrates, the sky over Paranal isn’t completely dark; after sunset, the beauty of the Universe is overshadowed by that of Earth’s own atmosphere, which glows in multiple hues and paints the sky like a watercolour. The playful brushstrokes of the faraway emission nebulae that adorn the Milky Way and the constellation of Orion (The Hunter) in the upper centre of the frame, are joined by the soft swaths of ...

29 March 2021: This gently glowing area of sky is actually a hot bubble of hydrogen gas — named Sh 2-305 — that has been bombarded by intense radiation from nearby stars. Such gas clouds are known as emission nebulae, or HII regions (pronounced “H-two”). The radiation in question is in the ultraviolet part of the spectrum and is thought to emanate from at least two O-type stars, and likely several others. This stellar class is the brightest and hottest that we know of — such stars can be up to 90 times as massive as the Sun, and an incredible one million times as bright. Together with five neighbouring bubbles, Sh 2-305 belongs to a giant complex of dense clouds of dust and gas and, on a larger scale, an enormous ring called the GS234-02 star-forming supershell (located in the Perseus arm of the Milky Way, in the constellation of Puppis). This ...

22 March 2021: Humans have gazed up at the skies for a very long time, fascinated by the flowing shape of the Milky Way, the bright lights of the stars and planets, and the dark patches that obscure regions of sky. Different cultures had various names for these features; this Picture of the Week shows one object that has taken on several different identities over time, alongside an antenna of the Atacama Large Millimeter/submillimeter Array (ALMA). At the very top of the frame, within the band of the Milky Way, lies a pair of bright stars. These form part of Crux (The Southern Cross), one of the most recognisable constellations in the southern sky. Just below Crux, a dark, irregular shape is silhouetted against the central band of our galaxy. This is a prominent dark nebula lying just 600 light-years away: a giant cloud of molecules so dense it blocks out the light ...

15 March 2021: At first glance, this image may be more than a little confusing — is the domed telescope at the centre of the image part of a framed roadside photograph? Is it floating in mid-air? What, exactly, is going on? Sadly, nothing as exciting as a levitating telescope — this is simply a trick of peculiar perspective and clever camerawork. Here, the Danish 1.54-metre telescope is perfectly framed and reflected in one of the many roadside mirrors around ESO’s La Silla Observatory. The telescope appears to point towards the Large Magellanic Cloud (LMC) as if it were observing. The LMC is a small nearby galaxy that orbits the Milky Way and can be seen lurking in the upper left of the image. Due to the extremely sensitive technique used, a soft green radiance known as airglow, caused by the faint emission of light in Earth’s atmosphere, can be seen sweeping across ...

8 March 2021: Even after the Sun has set over ESO’s Paranal Observatory in Chile, the site is not truly dark. Although light pollution is practically non-existent at the remote site high up in the Atacama Desert, as daylight disappears the flowing dunes are instead illuminated by the dazzling light streaming from the stars above. The only artificial illumination for miles around comes from Paranal’s facilities, including the telescopes themselves and the Residencia, photographed here. A true oasis in the desert, the Residencia is a refuge from the harsh environment of the Atacama. The astronomers and other employees who work at ESO’s Paranal Observatory, located just a few kilometres down the road and home to ESO’s Very Large Telescope, can escape the arid environment after a long shift and enjoy a walk through the indoor garden or a dip in the swimming pool. The Residencia’s striking visual design is complemented by its world-leading ...

1 March 2021: On occasion, the Atacama Large Millimeter/submillimeter Array (ALMA) at the Chajnantor plateau in northern Chile experiences something you might not associate with an astronomical observatory — snow! When snow falls and coats the landscape with a frosty glaze of cool white, the entire site is transformed. It becomes something almost subterranean or extra-terrestrial, reminiscent of a rebel base from Star Wars or a dystopian scene from Blade Runner. A number of ALMA’s 66 high-precision radio antennas can be seen in this image, connected by cleared pathways. The array spends its time observing the cool Universe and its phenomena — star formation, molecular clouds, and the early Universe.

22 February 2021: Appearing as a bird in flight, with wings outstretched in the expanse of space, SU Aur, a star much younger and more massive than the Sun, is surrounded by a giant planet-forming disc. This image, captured by the SPHERE instrument on ESO’s Very Large Telescope (VLT), shows the disc around SU Aur in unprecedented detail, including the long dust trails connected to it. The star itself is obscured by the instrument’s coronagraph, a device that blocks the light from the central star to allow the less bright features around it to stand out. The dust trails are composed of material from an encompassing nebula flowing into the disc. This nebula is likely the outcome of a collision between the star and a huge cloud of gas and dust, resulting in the unique shape of this planet-forming disc and the surrounding dust structure. A new study of SU Aur, which used ...