Picture of the Week 2021

27 December 2021: From its dome on Cerro Paranal in Chile’s Atacama desert, the ESO-operated Visible and Infrared Survey Telescope for Astronomy (VISTA) enjoys a stunning view of not only the majestic southern heavens, but also of the nearby mountainous peak, home to ESO’s Very Large Telescope (VLT). Conceived and developed by a consortium of 18 universities in the United Kingdom, VISTA is the world’s largest telescope entirely devoted to mapping the sky in infrared light. It carries out six public surveys taking up the majority of its observing time. The goal is to discover objects such as brown dwarfs, variable stars and ancient quasars, shed new light on fields such as the nature of dark matter and galactic structures, and even help create a 3D map of about five percent of the entire observable Universe. But why observe in the infrared? Because it allows VISTA not only to admire the cool side ...

20 December 2021: As 2021 comes to an end, we send our best wishes to you and your families! Like its predecessor, this last year has been challenging to most of us. Here at ESO we have worked hard to continue exploring the Universe and sharing its wonders with you while keeping our staff safe and protected. On behalf of everyone at ESO, we wish you a healthy end of the year and a wonderful start of 2022!

13 December 2021: This week’s picture may just hypnotise you! Resembling a vortex or an optical illusion, the starry circles draw you deeper into this breathtaking mountainous landscape of Chile’s Atacama Desert, home to ESO's La Silla Observatory. Each circular streak represents an individual star which maps out a star trail. Such trails are due to Earth’s rotation, which causes the stars to seemingly move across the sky, slowly tracing out perfect rings centred on the south celestial pole as they do so. A photograph like this therefore requires a long exposure to capture the passage of time. La Silla is located some 2400 metres above sea level, and offers perfect observing conditions for long-exposure shots like this; the site experiences over 300 clear nights a year! Here, ESO operates two of the most productive 4-metre class telescopes in the world: the ESO 3.6-metre telescope which is home to the world's foremost extrasolar ...

6 December 2021: This family portrait of the telescopes residing at ESO’s La Silla Observatory was captured in 2019 during the breathtaking sunset over the outskirts of Chilean Atacama Desert. Standing tall at the front of the portrait is one of La Silla’s new family members: BlackGEM, an array of optical telescopes which will join soon the search for some of the most powerful and dramatic events in the Universe, such as merging neutron stars and black holes. This robotic array was developed by Radboud University (from where it is remotely controlled), the Netherlands Research School for Astronomy (NOVA), and the KU Leuven. These exotic events cause ripples in the fabric of spacetime known as gravitational waves. BlackGEM will work together with gravitational wave detectors such as LIGO and Virgo to pinpoint in visible light the sources responsible for gravitational waves. This will allow for bigger telescopes — such as ESO’s Very Large ...

29 November 2021: Just as people at a busy crossroad may accidentally bump into each other, so too can galaxies in the Universe! But in this case, the outcome is more dramatic than a small nudge. When two galaxies clash, they merge into each other, giving birth to a new, bigger one. One example is the NGC 7727 galaxy, shown in this image from ESO’s VLT Survey Telescope (VST) in Chile. Located 89 million light-years away from Earth in the constellation Aquarius, NGC 7727 is believed to be the result of a clash between two galaxies that occurred about one billion years ago. The consequences of this tremendous cosmic bump are still evident in the peculiar, irregular shape of NGC 7727 and the streams of stars in its outer regions. The image was taken in visible light as part of the VST-ATLAS survey. The goal of the survey is to map a vast ...

22 November 2021: Powerful lasers leave the dome of one of the four Unit Telescopes of ESO’s Very Large Telescope (VLT) at Paranal Observatory in Chile. The beams reach a layer of the atmosphere about 90 kilometres above the ground, very rich with atoms of sodium. The lasers make the sodium shine, creating artificial stars in the sky. But why? Earth’s atmosphere distorts light reaching us from cosmic objects, decreasing the sharpness of astronomical observations. This is the same reason why stars seen from Earth appear to “twinkle”. To correct observations for this effect, astronomers have developed a technology known as adaptive optics, where a flexible mirror is deformed hundreds of times per second to counteract atmospheric turbulence. However, to calculate the necessary corrections, adaptive optics need reference stars close to the observed object. Such stars are not always ideally placed, though, which made astronomers come up with the idea of using lasers ...

15 November 2021: Yes, the bright light you see in the centre of this picture, shining below the Milky Way’s dark, pinkish belt, is in fact the king of the planets in the Solar System! Jupiter is flanked by two hills hosting ESO’s Very Large Telescope (left) and VISTA (right) in the Atacama Desert in Chile. Jupiter is the largest planet in our Solar System and the third brightest object in the night sky, only outshone by the Moon and Venus. Naming it after the god of the sky and thunder is certainly fitting! Mainly made of hydrogen and helium, one of Jupiter’s most distinctive marks is the famous great red spot on its surface, the largest storm in the Solar System. Jupiter has been observed by the 8.2-m telescopes of the VLT on more than one occasion. The VISIR instrument captured a stunning high resolution infrared image of Jupiter, key to understanding ...

8 November 2021: The image shows a pair of overlapping spiral galaxies, NGC 3314a and b, in the top left, caught in a majestic cosmic dance — captured by ESO’s VLT Survey Telescope (VST). But don’t let the perspective fool you! They are, in fact, not interacting at all. The two galaxies, located between 117 and 140 million light-years away in the constellation of Hydra, are actually physically unrelated and only appear to overlap when viewed from Earth. This unique alignment gives astronomers the opportunity to measure many properties of the galaxies, such as how dust absorbs starlight, and hence gain insight into their composition and evolution. There is another hidden secret in this picture if you look closely at the lower right region: beyond this stunning cosmic dance you will find a faint yellowish smudge, the signature of an ultra-diffuse galaxy (UDG). UDGs are objects as large as the Milky Way but ...

1 November 2021: The Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS) telescopes sited at ESO’s Paranal Observatory in Chile’s Atacama Desert are usually the ones looking for new worlds, but this picture actually captures the observing site looking like a planet itself. This is constructed using a photography technique called stereographic projection, whereby a spherical image — like a 360º panorama — is projected onto a plane. The mission of SPECULOOS is to detect terrestrial planets as they pass between us and their parent small, cool star in the solar neighbourhood, leading to a tiny, regular dimming in the star’s brightness. Exoplanets discovered by this so-called transit method can be studied in great detail, including making precise measurements of their mass and radius, and analysing their possible atmospheres and potential for life. SPECULOOS, whose name is inspired by the sweet treat famous in Belgium, The Netherlands and Germany, comprises four telescopes, each ...

25 October 2021: Captured with the MUSE instrument mounted on ESO’s Very Large Telescope (VLT), this image shows the innermost regions of the distant spiral galaxy NGC 5248, also known as Caldwell 45. Located around 59 million light-years away from Earth, in the constellation of Boötes, this galaxy is notable for having not one but two rings around its centre. These rings are characterised by “hot spots” of starburst activity. Starburst regions, seen as an orange glow in the picture, are where stars form much more frequently than usual. MUSE, which stands for Multi Unit Spectroscopic Explorer, is attached to Yepun, one of the four 8.2-metre telescopes that make up the VLT. MUSE decomposes the light of every single pixel within its field of view into its constituent colours or wavelengths. This allows researchers to map complex mechanisms within extended objects, such as analysing the formation of stars in galaxies.

18 October 2021: Cast against the background of a magnificent sunset above the Chajnantor Plateau in the Atacama Desert, the antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) keep watch over the skies. ALMA, of which ESO is a partner, is the largest ground-based astronomical project in existence. The beautiful shades of orange and red that illuminate the sky as the Sun sets behind the horizon teach us an interesting physics lesson. As it passes through the Earth’s atmosphere, sunlight with shorter, bluer wavelengths gets scattered off the molecules of gas and dust in the air more than that with longer, redder wavelengths. As the Sun approaches the horizon, light that reaches the Earth’s surface takes a longer path through its atmosphere, and most of the blue part of its visible spectrum gets scattered away. The light that reaches our eyes dyes the sky around the setting Sun in stunning hues of red. ...

11 October 2021: A person’s welcoming silhouette is outlined against one of the Auxiliary Telescopes (ATs) at ESO's Paranal Observatory in the Atacama Desert of Chile, as the coalsack nebula waves its majestic hello as a dark smudge in the middle of the night sky. This is one of ESO’s Very Large Telescope’s four 1.8-metre Auxiliary Telescopes, which also includes four giant 8.2-metre cousins, the Unit Telescopes (UTs). Depending on the needs of each observing project, the ATs can be repositioned in up to 30 different observing locations along a system of tracks and act together as part of the VLT Interferometer. The interferometer combines the light the ATs or the UTs capture from celestial objects with a technique known as interferometry, allowing researchers to observe the cosmos in incredible detail. The Coalsack Nebula is the most prominent dark nebula in the sky. In the Southern hemisphere, these dark clouds are more prominent ...

4 October 2021: Each family has its own traditions and the staff at ESO’s Paranal observatory in the Atacama Desert of Chile are no exception. Before the observations start, people meet on the observatory’s platform to enjoy the sunset, accompanied in this picture by one of the 1.8-metre diameter Auxiliary Telescopes (ATs) of ESO’s Very Large Telescope (VLT). The ATs can be moved along rails, and they work together as a single, “virtual” instrument, the Very Large Telescope Interferometer (VLTI), which uses interferometry to combine the light collected by the individual telescopes and probe the cosmos with much sharper eyes. The VLT also comprises four static 8.2m Unit Telescopes, which can work either as standalone telescopes or with the VLTI. The orange colour of the Sun and the sky at sunset is caused by the Earth’s atmosphere. This scatters the light reaching the Earth from space in different directions, depending on the colour. ...

27 September 2021: The low twilight Sun highlights the clouds hanging over the Chilean Atacama landscape in this Picture of the Week, bathing the scene in deep, fiery red light. The image is dominated by the Purico Complex, a clump of volcanic mountains whose highest peak reaches a whopping 5703 metres in elevation! A single vehicle is visible on the remote road below, kicking up a stream of opaque dust in its wake, and towards the left of the image is a cluster of buildings...and a single antenna. This is the ESO-operated Atacama Pathfinder Experiment (APEX), one of the highest telescopes in the world. APEX is designed to work at submillimetre wavelengths between infrared light and radio waves, which are key to revealing some of the coldest, dustiest, and most distant objects in the Universe. Over the years, it has explored a wide range of astronomical phenomena, probing the wild early lives of ...

20 September 2021: In this Picture of the Week, taken by drone, you can see nearly all of the telescopes at ESO’s La Silla Observatory snaking along the top of the 2400-metre saddle-shaped mountain and into the distance. One for the La Silla family album! La Silla is located on the outskirts of Chile’s Atacama Desert, far from human-made light pollution in an area famed for its dark, clear skies. It was ESO’s first observatory, inaugurated in 1969, and remains at the forefront of astronomy today, with around 300 scientific papers using observations from La Silla telescopes published every year. The most prominent telescope in this image is the ESO 3.6-metre telescope, home to the world's foremost exoplanet hunting instrument: the High Accuracy Radial velocity Planet Searcher, or HARPS. Thanks to the observations made with HARPS, astronomers have worked out that there are likely billions of rocky planets in the temperate zones around ...

13 September 2021: Looking at this photo might make you feel a little topsy-turvy! This Picture of the Week captures both the Northern and Southern Hemisphere at once — the whole night’s sky in one mind-bending image — something that would be impossible to see in real life. To create this image, photographers Petr Horálek and Juan Carlos Casado took two pictures at observatories located at the same latitudes in the Northern and Southern Hemispheres. The top half is a photo taken at the Instituto de Astrofísica de Canarias’ Roque de los Muchachos Observatory in La Palma in the Canary Islands, 29 degrees north of the equator, whilst the bottom half was taken at ESO’s La Silla Observatory in Chile’s Atacama Desert, 29 degrees south of the equator. When digitally stitched together, they create a continuous sweeping view of the night’s sky. One of the most noticeable features in this picture is the ...

6 September 2021: Like Atlas holding up the sky in the Ancient Greek myth, it looks like ESO’s Very Large Telescope (VLT) is supporting the Moon in this extraordinary picture of a total lunar eclipse at the Paranal Observatory in Chile’s Atacama Desert. The photograph was taken on 26 May 2021 by astrophotographer Yuri Beletsky and it is featured in the ESO Calendar 2022. To take this Picture of the Week, some detailed planning was required on the part of the photographer. Careful calculations allowed him to pinpoint a location nine kilometres to the east of Paranal, where the setting lunar eclipse would be briefly visible just above the domes of the telescopes, glowing faintly in the early morning twilight. A total lunar eclipse occurs when the Sun, Earth and Moon align, with the Earth between the Sun and Moon. The Earth’s shadow blocks direct sunlight, so that the only light reflected from ...

30 August 2021: How does a fish see the Milky Way? We can get a pretty good idea thanks to this picture of our galaxy, taken with a fisheye lens from the entrance of the Paranal Residencia at the Paranal Observatory’s Base Camp, located 3 km away from ESO’s Very Large Telescope (VLT). The Paranal Residencia is a true “oasis for astronomers”. Located in the Atacama desert, one of the driest regions on our planet, it is a comfortable and modern building where ESO staff and visitors can rest during their long shifts and withstand the extreme local climatic conditions. The Residencia is a subterranean construction with a 35-metre wide glass-covered dome, which brings in natural light, and a swimming pool, which helps the staff to relax and also contributes to the building’s humidification system. The building’s facade opens towards the Pacific Ocean, just 12 kilometres away. From its southern latitude, Paranal offers ...

23 August 2021: A meteoroid lights up the night sky at Paranal in the Chilean desert, with three Unit Telescopes and one Auxiliary Telescope of ESO’s Very Large Telescope (VLT) witnessing the end of its journey across the Solar System in a stunning burst of light. Smaller than asteroids, meteoroids are rocky objects wandering through space. When they enter the Earth’s atmosphere, they heat up and vaporise due to friction with the air, leaving behind a luminous trace in the sky known as a shooting star (or meteor). The remains of a meteoroid which are not entirely vaporised and reach the ground are called a meteorite. The colour of the luminous trace reveals the chemical composition of the meteoroid which left it. Green and yellow lights indicate the presence of magnesium and iron, respectively. The diffuse red glow across the sky is emitted by the oxygen and nitrogen in the Earth’s atmosphere. ESO’s ...

16 August 2021: Dark lines criss-cross the Chilean sky at ESO’s Paranal Observatory, making the brightest region of the Milky Way play hide-and-seek with ESO’s VISTA telescope. These lines, known as the Great Rift, are immense clouds of gas and dust located between the Solar System and the internal regions of the Milky Way. These clouds absorb most of the visible light trying to reach us from the billions of stars in the centre of our galaxy. Nonetheless, astronomers are still able to probe the inner Milky Way by observing infrared and radio light, which passes through the clouds without being absorbed, allowing us to literally “look through” the great rift. Part of ESO’s Paranal Observatory, the Visible and Infrared Survey Telescope for Astronomy (VISTA) is located on the peak next door to the one where the ESO Very Large Telescope (VLT) is perched. It is one of the largest telescopes for stellar ...