Atop the mountain Cerro Armazones in Chile, construction is underway on the Extremely Large Telescope (ELT), which will usher in a new era of astronomy when it's completed. The ELT will be the world's largest telescope, with a primary mirror that measures 128 feet (39 meters) across.

What is it?

Astronomy depends as much on location as it does on technology. To observe the faintest and most distant objects in the universe, telescopes need dark, dry and stable skies, conditions that are increasingly rare on Earth. Mountains in the Chilean Atacama Desert, like Cerro Armazones, offer an almost perfect natural laboratory. Situated at high altitude, far from cities, and in one of the driest places on the planet, they provide exceptionally clear nights with minimal atmospheric disturbance.

For more than six decades, this environment has made Chile the global center of ground-based astronomy. The European Southern Observatory (ESO) operates all of its observatories here, including the Very Large Telescope (VLT) at Cerro Paranal and, soon, the ELT. Together, these facilities represent humanity's ongoing effort to understand the cosmos, from nearby exoplanets to the earliest galaxies.

Where is it?

The ELT is under construction atop Cerro Armazones, which is a mountain in Chile's Atacama Desert.

Why is it amazing?

Scientifically, the ELT represents a transformative leap. With its massive mirror and advanced instruments, it will be able to directly image exoplanets, analyze their atmospheres for signs of habitability, study the formation of stars and galaxies, and probe the nature of dark matter and dark energy. The proximity of ELT and VLT reflects continuity in scientific progress, with each new generation of telescopes building upon the legacy of the last.

Want to learn more?

You can learn more about the Extremely Large Telescope and other ground-based telescopes.

German Nobel Prize-winning astrophysicist Reinhard Genzel has penned a letter urging the government of Chile to halt the development of a green hydrogen plant in the vicinity of one of the world's top astronomical observatories.

In the letter, Genzel and 30 other world-leading astronomers urge Chilean leaders to protect the pristine, unpolluted night sky above Cerro Paranal, an 8,740-foot-high (2,664-meter) peak in the Atacama Desert that is home to the European Southern Observatory's (ESO) most valuable astronomical observatories including the Extremely Large Telescope (ELT), which when built will be the world's largest telescope.

The astronomers believe that the Paranal Observatory, currently considered among the least light-polluted astronomical sites in the world, will suffer if a planned clean hydrogen plant gets a go-ahead. "As currently conceived, the project represents an imminent threat to some of the most advanced astronomical facilities on Earth, operating under one of the world's last pristine dark skies," the scientists wrote in the letter, criticizing the placement of the clean hydrogen plant, called INNA, just a few miles from the summit of Cerro Paranal. "Earlier this year, an in-depth, data-driven technical analysis by ESO revealed that INNA would cause an increase of up to 35% in light pollution above Cerro Paranal."

It's not just light pollution that poses a threat, however. the letter continues. The signing scientists write that the same analysis "also revealed other impacts of the project, from creating micro-vibrations that will negatively affect and possibly impede the operation of some of the most cutting-edge astronomical facilities, to increasing turbulence that blurs our view of the universe."

The Paranal Observatory is home to the Very Large Telescope (VLT), which is actually a quartet of telescopes with 27-foot-wide (8.2 meters) mirrors that can work in concert as a so-called interferometer to maximize the facility's sky-observing abilities.

Genzel, who won the 2020 Nobel Prize in Physics for his research of the Sagittarius A* black hole at the heart of the Milky Way galaxy, used VLT to observe the movements of stars close to the galaxy's center to determine the black hole's properties.

Cerro Paranal is also home to the Cherenkov Telescope Array, the world's most powerful observatory for research of high-energy gamma rays, extremely energetic radiation emitted from black holes and released in supernova explosions. According to the ESO analysis, the Cherenkov array could suffer an up to 50% light pollution increase from the proposed plant, being located only 3 miles (5 kilometers) away from the prospected site.

The astronomers think that interference from the hydrogen plant might degrade Paranal from being the world's premium astronomy site to a merely mediocre one.

"We might lose the ability to observe about 30% of the faintest galaxies," Xavier Barcons, ESO's Director General, told Space.com in an earlier interview. "We are at the point of starting to be able to see details of exoplanet atmospheres, but if the sky gets brighter, we may not be able to see those details anymore."

The unspoiled nature of the Paranal sky, together with the world's most favorable weather conditions for astronomy, prompted ESO to choose the neighboring Cerro Armazones as a site of the next-generation ELT. ELT, currently under construction, will be fitted with a single 130-foot-wide (39.3m) mirror and will become the world's largest telescope capable of studying the universe in visible light.

The $1.4-billion observer should enable astronomers to directly image exoplanets orbiting nearby stars and observe the most distant galaxies. The presence of INNA, however, is likely to increase the brightness of the sky above ELT by 5%, reducing the telescope's scientific potential.

The $10 billion INNA renewable hydrogen plant, developed by the U.S.-headquartered energy company AES, will spread across 7,500 acres (3,021 hectares) of land and consist of three solar farms, three wind farms, a battery energy storage system and facilities for the production of hydrogen.

AES submitted its environmental assessment for the development a year ago and is awaiting a decision by local authorities. The astronomers call for the plant's relocation away from Atacama's precious observatories.

"While we recognize the need, both in Chile and globally, to develop green energy facilities, the proximity and extent of the infrastructure associated with the INNA project pose a grave threat, which cannot be mitigated given the closeness of the planned installation to the observatory," the scientists wrote in the letter. "We are convinced that economic development and scientific progress can and must coexist to the benefit of all people in Chile, but not at the irreversible expense of one of Earth's unique and irreplaceable windows to the universe."

AES previously told Space.com that the site's impact on the Paranal night sky would be negligible.

High atop the arid plateaus of Chile's Atacama Desert, one of humanity's most powerful astronomical instruments peers into the depths of the cosmos: the Very Large Telescope (VLT). Operated by the European Southern Observatory (ESO), the VLT has long been at the forefront of astronomical discovery, as scientists use its cutting-edge technology to explore distant galaxies, and some, like our own Milky Way, that are closer to home.

What is it?

Three of the VLT's massive domes were recently treated to this view of the Milky Way. Above the observatory, a soft green and red glow, known as airglow, helps to tinge the horizon. Airglow is a natural phenomenon arising from chemical reactions high in Earth's upper atmosphere, where atoms and molecules release light in the process. Depending on which elements are involved, airglow can appear in subtle shades of green, red or orange.

Where is it?

The VLT is based in the Andes Mountains in the Atacama Desert.

Why is it amazing?

Airglow is incredibly faint, and invisible in most parts of the world because of widespread light pollution. Only in some of Earth's darkest places, such as the Atacama Desert, can this natural radiance be seen. It is precisely these conditions that make the VLT's site one of the best observing locations on the planet.

Astronomers are increasingly concerned that even remote observatories like the VLT may one day face the creeping glow of artificial light. Urban expansion, satellite constellations and industrial development all threaten to erode the natural darkness that makes sites like the Atacama Desert invaluable. Protecting these rare darkness sanctuaries is not only an environmental issue, but a scientific and culture one.

Want to learn more?

You can learn more about the Very Large Telescope and ground-based telescopes.

Behold the golden-orange horizon over Kitt Peak National Observatory, a fiery twilight moment where day bows out and the stars prepare their grand entrance. Captured by NOIRLab, this sunset reveals the pristine conditions that make Kitt Peak such a favorable astronomical site.

What is it?

Founded in 1964, the Kitt Peak site was chosen by the National Science Foundation to house a national observatory capable of delivering clear, dark-skied views of the cosmos. There, more than two dozen optical and radio telescopes now share the peak with ancient desert winds and perhaps, in the spirit of Halloween, a few ghost stories yet untold.

Over the decades, the observatories on Kitt Peak have helped map dark matter, chart distant galaxies and train generations of astronomers.

Where is it?

Kitt Peak is in the Baboquivari Mountains of southern Arizona, 56 miles (90 kilometers) southwest of Tucson on land owned by the Tohono O'odham Nation. The telescope complex sits at an elevation of about 7,000 feet (2,100 meters).

Why is it amazing?

The vivid orange sky at Kitt Peak National Observatory is more than just a Halloween color; it shows the dry air and lack of light pollution at the site, two things needed for pristine astronomy. As even the tiniest speck of dust, or nearby city lights can break equipment or make noise in readings, remote areas like Kitt Peak offer sanctuary to astronomers peering deep into space.

Want to learn more?

You can learn more about ground-based telescopes and observatories.

As one half of the International Gemini Observatory, the Gemini North telescope in Hawaii provides astronomers with a window into the distant universe, from growing stars to evolving galaxies.

Its twin, Gemini South, is located in the Atacama Desert in Chile. Together, these telescopes form a powerful duo that allows astronomers to observe the entire sky from both hemispheres.

What is it?

In this long-exposure image, the lines of light in the night sky are caused by both stars and satellites moving across the heavens. Satellite streaks in particular are becoming a growing issue for telescopes like Gemini North and Gemini South, as they can affect the accuracy of measurements.

Where is it?

The Gemini North telescope is located on top of Mauna Kea in Hawaii.

Why is it amazing?

In recent years, the growing number of satellites in orbit has increased dramatically as private companies like SpaceX and Amazon launch large satellite constellations to deliver global broadband internet and other services. While these networks bring important technological advances, their presence also means more bright objects moving in the sky.

For observatories like Gemini North and Gemini South, this poses a serious issue. The reflected light from satellites can contaminate astronomical images, obscuring faint celestial objects or creating unwanted artifacts in valuable data. These disruptions make it harder to study phenomena like distant galaxies, near-Earth asteroids and the subtle signatures of exoplanet atmospheres.

To help mitigate this problem, the U.S. National Science Foundation's NOIRLab, which helps run both Gemini North and Gemini South, co-hosts the Center for the Protection of the Dark and Quiet Sky (CPS), a global collaboration that coordinates research and advocacy efforts to preserve our natural view of the cosmos.

Want to learn more?

You can learn more about satellite pollution and working to protect dark skies.

High in Chile's Atacama Desert, one of the driest and most remote places on Earth, sits the Atacama Large Millimeter/submillimeter Array (ALMA). Operated by the European Southern Observatory (ESO) and its international partners, ALMA is not a single telescope but an array of 66 high-precision antennas that together probe the universe in wavelengths unseen by human eyes.

What is it?

Unlike optical telescopes, ALMA observes in the millimeter/submillimeter range, between infrared and longer radio waves. These wavelengths allow astronomers to study regions where young stars are shrouded by dust or where galaxies lie so far away that their light has stretched and cooled during its journey across space and time.

ALMA's antenna's are spread out across the desert plateau in various configurations. The assemblage operates essentially as a single, giant telescope with extraordinary resolution, sharp enough to discern the tiniest of details.

Where is it?

The radio dish array sits on the Chajnantor Plateau, at an altitude of 16,500 feet (5,000 meters) above sea level.

Why is it amazing?

The high altitude of the Chajnantor Plateau provides the perfect vantage point for radio astronomy: here the air is thin and dry, with little water vapor to absorb faint cosmic signals. Looming over the site is the majestic Licancabur volcano, its snow-dusted summit and crater lake watching silently over the antennas below.

Under Licancabur's watchful eye, ALMA continues to gaze deeper into the cold, hidden corners of the universe.

Want to learn more?

You can learn more about ALMA's findings and other telescopes in Chile.

The Vera C. Rubin Observatory has begun its decade-long survey to scan the entire night sky every three days. To do this, it uses the Simonyi Survey Telescope and the Legacy Survey of Space and Time (LSST) camera, the world's largest digital camera.

What is it?

Together, the telescope and camera work to make this process as efficient as possible. The Simonyi Survey Telescope has an advanced drive system that allows it to move more quickly than any other telescope of its size, completing an exposure and repositioning itself for the next image in as little as five seconds, allowing Rubin to scan the sky at an unprecedented pace.

Similarly impressive, the LSST camera has a massive focal plane that can cover an area of the sky 45 times larger than the full moon with every exposure, building an ever-expanding record of a universe in motion.

Where is it?

This long-exposure image was taken at the Vera C. Rubin Observatory at Cerro Pachón in Chile.

Why is it amazing?

The glowing streaks in this long-exposure image show how often and how fast the Simonyi Survey Telescope spins as it scans the night skies. This scanning will continue for years to come as the Vera Rubin Observatory continues its Legacy Survey of Space and Time flagship project. Over the course of a decade, Rubin will repeatedly scan the entire visible sky, creating a dynamic portrait of cosmic change in the universe.

The LSST is designed to track the shifting positions of asteroids and other near-Earth objects, monitor the flickering of stars and capture the explosive brilliance of supernovae. Beyond these immediate discoveries, Rubin will also probe some of the most profound mysteries in modern science: the nature of dark matter and dark energy.

Want to learn more?

You can learn more about the Rubin Observatory and dark matter.

Night after night in the dry air of Chile's Atacama Desert, fine dust and pollutants settle on the aluminum coating of the mirrors belonging to the Very Large Telescope, part of the European Southern Observatory (ESO). This process degrades the mirrors' reflectivity and clarity over time, so technicians regularly recoat and polish them to ensure the best precision.

What is it?

Keeping a 25-ton (23 metric tons) mirror in perfect condition is a delicate process. For light cleaning, technicians sometimes spray frozen carbon monoxide across the surface to dislodge the dust. Eventually, however, the thin aluminum coating has to be replaced.

After the mirror is painstakingly removed from its mount, engineers check for particles and chemically strip away the old layer of aluminum before adding a shiny new layer just 80 nanometers thick, a thousand times thinner than a human hair.

Where is it?

This image was taken at the VLT basecamp at the foot of Cerro Paranal.

Why is it amazing?

The VLT has delivered some of the most detailed observations of our universe. From imaging exoplanets to probing the environments around supermassive black holes at the centers of galaxies, the VLT has pushed the limits of what ground-based telescopes can achieve.

Want to learn more?

You can read more about the Very Large Telescope and other telescopes in Chile.

An enormous piece of glass-ceramic has been cast for the secondary mirror of the European Southern Observatory's (ESO) Extremely Large Telescope, entering a year-long cooldown and heat-treatment period until it's ready to be ground and polished for use with the megatelescope.

The completed mirror will measure nearly 14 feet across (4.2 meters) and weigh 3.9 tons (3.5 metric tons) — larger than the primary mirror for many current research telescopes, ESO officials noted in a statement. For the Extremely Large Telescope, though, the mirror will be suspended upside down over the 128-foot (39 meter) primary mirror, which is made of 798 hexagonal mirror segments. The telescope is scheduled to reach first light in 2024 on a mountain in Chile's Atacama Desert. ESO documents the casting process in a new video.

After the year of cooling, the mirror base will be transported from Germany to France, where it will be ground into a precise convex shape and then polished precisely to within 15 nanometers to meet the giant telescope's needs. According to the ESO, the piece will be the largest convex mirror ever produced and the largest secondary mirror to be used in a telescope.

The mirror is made from a special ceramic-glass material manufactured by the glass company Schott, which is used in many astronomical telescopes. The compound has very little thermal expansion when exposed to different temperatures, to avoid distorted measurements; it can be polished very precisely; and is chemically resistant, the statement said.

The ESO also contracted with Schott for the base of the third mirror, and for the flexible fourth mirror, which has already been delivered. (A total of five mirrors make up the telescope's unusual structure.) 

Once complete, the telescope will survey the universe in optical and infrared light, letting scientists probe deep into the universe's past to see how galaxies have evolved and pinpoint planets around distant stars, searching for signs of biological activity. There are two other megatelescopes under construction on a similar time frame that could share the burden of discovery: The Giant Magellan Telescope, also slated for the Atacama Desert, with a maximum 80-foot (25 m) light-gathering surface, and the Thirty Meter Telescope in Hawaii, whose light-gathering surface would stretch to 98 feet (30 m).

Email Sarah Lewin at slewin@space.com or follow her @SarahExplains. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com. 

The world's largest telescope has gotten its official construction go-ahead, keeping the enormous instrument on track to start observing the heavens in 2024.

The European Extremely Large Telescope (E-ELT), which will feature a light-collecting surface 128 feet (39 meters) wide, has been greenlit for construction atop Cerro Armazones in Chile's Atacama Desert, officials with the European Southern Observatory (ESO) announced Thursday (Dec. 4).

"The decision taken by Council [ESO's chief governing body] means that the telescope can now be built, and that major industrial construction work for the E-ELT is now funded and can proceed according to plan," Tim de Zeeuw, ESO's director general, said in a statement. "There is already a lot of progress in Chile on the summit of Armazones, and the next few years will be very exciting." [Photos: World's Largest Telescope Being Built in Chile]

E-ELT construction was first approved in June 2012, but on the condition that contracts worth more than 2 million euros ($2.48 million at current exchange rates) could be awarded only after 90 percent of the total funding required to build the telescope (1.083 billion euros, or $1.34 billion, at 2012 prices) had been secured. An exception was made for "civil works," including the leveling of the site and a road up Cerro Armazones, ESO officials said.

The 90-percent threshold was reached in October, when Poland agreed to join ESO, officials said, but making the numbers work took some tweaking. ESO split E-ELT development into two phases: 90 percent of the project's costs go toward "Phase 1," which will get E-ELT up and running, and 10 percent of the costs are allocated to "Phase 2," for the development of nonessential elements. These include about one-quarter of E-ELT's 798 individual mirror segments (which together make up the huge main mirror) and part of the telescope's adaptive optics system, which helps cancel out the blurring effects of Earth's atmosphere.

The current construction approval applies only to Phase 1; contracts for this work will be awarded in late 2015. The Phase 2 components will be approved as more funding becomes available, ESO officials said.

"The funds that are now committed will allow the construction of a fully working E-ELT that will be the most powerful of all the extremely large telescope projects currently planned, with superior light-collecting area and instrumentation," de Zeeuw said. "It will allow the initial characterization of Earth-mass exoplanets, the study of the resolved stellar populations in nearby galaxies as well as ultra-sensitive observations of the deep universe."

As de Zeeuw said, E-ELT is not the only giant ground-based telescope in the works. The Giant Magellan Telescope (GMT) will soon start taking shape atop Las Campanas, another Chilean peak. GMT will arrange seven 27.6-foot-wide (8.4 m) primary mirrors into one light-collecting surface 80 feet (24 m) across; project officials are aiming for "first light" in 2021.

And the Thirty Meter Telescope (TMT) — which, not surprisingly, will boast a light-collecting surface 30 m, or 98 feet, wide — is slated to start observing from Hawaii's Mauna Kea in 2022. Like E-ELT, TMT's primary mirror will be composed of hundreds of relatively small segments.

All three megascopes should help researchers tackle some of the biggest questions in astronomy, including the nature of the mysterious dark matter and dark energy that make up most of the universe.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.

The Hubble SpaceTelescope may take photos of the universe's deepest reaches, but some groundtelescopes may now get a "Lucky" leg-up on image clarity.

Using thenew "Lucky Imaging" system, a team of astronomers claims to havetaken pictures of stars twiceas sharp as those produced by Hubble.

?These arethe sharpest images ever taken either from the ground or from space," saidCraig Mackay, an astronomer at the University of Cambridge in England who led the research.

Mackay andhis colleagues' findings are presented on the Web site for the Institute of Astronomy at the University of Cambridge.

Twinkle stopper

Earth'sfluctuating atmosphere not only causes stars totwinkle, but also blurs the photos of astronomers trying to snap clearimages of the cosmos.

Sensitivecameras can beat the blurriness, but they produce grainy "noise" thatcan make images nearly unusable. On the other hand, space telescopes such asthe Hubble avoid the problem by orbiting above Earth's atmosphere altogether,yet they carry billion-dollar price tags.

To create aground-based system that could beat noise and fit a budget, Mackay and his teamused power in numbers. Their new imaging system takes pictures at 20 frames persecond, chooses the best of tens of thousands of images, merges them togetherand eliminates random noise.

?To produceimages sharper than Hubble from the ground is a remarkable achievement byanyone?s standards," Mackay said of the system, adding that its estimatedcost of about $100,000--less than a hundredth of a percent of the Hubble spacetelescope's growingprice tag--is an even greater achievement.

Telescopetest

Theastronomers tested the Lucky Imaging system with a 200-inch (5.1-meter)telescope at the Palomar Observatory in San Diego, Calif. The observatorynormally produces images 10 times less detailed than Hubble's, but the newcamera created images twice as sharp as those of the space telescope.

Mackayexplained that the performance boost came from comparingtwo images of the globular star cluster M13.

"Thestar cluster image already shows we can exceed Hubble's clarity, but we thinkwe can do much better," Mackay told SPACE.com. The astronomernoted, however, that Hubble has a better ability to take longer exposures andproduce "deeper" views of the cosmos.

Mackay thinksthe new imaging system's most effective use will be in larger telescopes, whereit can be used to expand the search for mysteriousdark matter.

?The imagesspace telescopes produce are of extremely high quality, but they are limited tothe size of the telescope,? Mackay said. ?Our techniques can do very well whenthe telescope is bigger than Hubble and has intrinsically better resolution.?

The onecatch for Mackay's new system: Clear conditions and plenty of time are requiredto produce crisp images that exceed Hubble's abilities.

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