From the platform of the VLT, looking east, the first hint of daylight emerges. The Milky Way arcs overhead, looking close enough to be the central beam in a vast cathedral ceiling
Credit: ESO
Sunset over the Very Large Telescope on the 2, 600-metre-high Cerro Paranal in the Atacama Desert, Chile
Credit: ESO
EVEN WHEN YOUR brain knows you're looking at the VLT your eyes refuse to believe it. Seen from a distance, the Southern Hemisphere's largest astronomical facility, aptly named the Very Large Telescope, looks like a mirage or a sci-fi special effect - an impossibly large and elaborate structure grafted onto an equally alien-looking landscape.
In my case, the otherworldly effect is augmented by a four hour drive from the city of Calama, across some of the most barren and rugged terrain in the world.
This is a desert made of endless mountains, running north to south in three great ranges. Of these, the Cordillera de la Costa is nearest to the sea. Turning off the Pan-American Highway, we follow a side road deep into the range until another turn takes us up a steep rise.
As we round a bend, the top of Cerro Paranal, a 2,600-metre-high peak, suddenly slides into view. The mountain is sprouting four monolithic cylinders, each housing one of the European Southern Observatory's four identical 8.2-metre telescopes. The sky overhead is a brilliant blue.
Marine biologists have their coral reefs, particle physicists have the Large Hadron Collider, but when it comes to astronomy, nothing is closer to paradise than this desolate stretch of northern Chile known as the Atacama Desert.
Billed as the driest place on Earth, the region's parched climate, high altitude and extreme temperatures imposed severe constraints on the first people to settle here thousands of years ago, just as it later dismayed conquistadors in search of easy gold.
Over geologic time, the dry environment produced and preserved extensive salt deposits, along with sodium nitrate useful for fertiliser and explosives - a once-precious natural resource which, in 1879, led the Chilean government to seize the Atacama, sparking a bloody war with Bolivia and Peru.
Today, another resource - smooth-flowing, clear, dry air - is drawing astronomers to the Atacama in droves, and the invasion is ramping up. One or more of three giant optical telescopes currently in development will be situated somewhere in the region.
The world's most advanced radio observatory is already under construction here. The reason is not that the mountains of the Atacama are the highest in the world, but that they offer a steady, cloudless view of the night and are about as close to the conditions of space as you can get from the Earth's surface.
"We're observing practically all the time," says Chris Lidman, a senior astronomer at the VLT. Although the Pacific is in plain sight, a mere 12 kilometres from the summit of Paranal, the mountain paradoxically receives less than 10 mm of precipitation annually. The VLT rarely loses a night to poor weather. "It's really a special place," he says.
It is also an incredibly unlikely one. A desert mountaintop is not made for human inhabitants. To comfortably maintain over 100 observatory visitors and personnel working each day and night, the VLT requires a steady stream of materials and supplies, including food and water, all of which must be trucked in from the coastal city of Antofagasta, an hour's drive away.
Because there is nowhere nearby to stay, the observatory residence operates as a full service hotel, complete with all-night cafeteria and swimming pool. Built partly into the mountainside, the residence has an understated exterior that sets up visitors for a major surprise: coming in from a blazing hot desert afternoon, a set of heavy double doors opens onto a lush, climate-controlled atrium full of tropical plants. The setting is an immediate antidote to the desiccated extremes of the Atacama.
Its incongruous luxury also conjures up the image of an evil genius' secret lair, & agrave; la James Bond. No wonder that Hollywood came to Paranal recently to film sequences for the latest Bond flick, A Quantum of Solace. Yet the movie doesn't do justice to
the real thing.
The aesthetics of Paranal may be an anomaly in modern astronomy, but the way science is done here is not. Four hundred years ago Galileo changed the world by pointing a hand-built telescope toward the heavens and reporting what he saw. Today, Galileo's intellectual descendants are doing the same thing at the VLT, using optical principles that Galileo would presumably have grasped, but at an industrial scale that would have set his head spinning.
The observatory's sprawling control room is a hive of activity by 4 pm. Each of the four large unit telescopes and a smaller survey telescope is manned by its own dedicated team preparing for the night ahead. A sixth telescope, British-built VISTA, is located on an outlying spur with its own separate control area.
Lidman, who is overseeing the night's activities, meets with engineers and astronomers to discuss the evening's agenda and to review any problems that arose the night before. "My main goal is to make sure that all the telescopes are ready at the beginning of each night," he says.
Efficiency is key. Much of the observing at VLT is done in 'service mode', which means astronomers do not visit Paranal but rather have their requested observations conducted by ESO staff. This approach has some big advantages, since observations can be scheduled and rescheduled to optimize scientific returns without the need to juggle travel schedules.
About one third of the time, observations may require immediate feedback or be sufficiently complex to merit investigators coming to the VLT in person.
Tonight a team of visiting German astronomers are working with Unit Telescope 1, also known as 'Antu' (the word for Sun in Mapudungun, an indigenous Chilean language). The three other unit telescopes, 'Kueyen' (Moon), 'Meilipal' (the Southern Cross) and 'Yepun' (Venus) are all running in service mode.
Having four identical telescopes has definitely helped the VLT become the astronomy factory it is today. Because each carries its own suite of instruments, the VLT can make many different kinds of observations in one night without pausing to switch hardware.
"The VLT is, without question, the best instrumented observatory in the world," says astronomer Ray Carlberg of the University of Toronto. "That has allowed its user community to take the lead in some important areas."
While tourists can arrange to visit the VLT during the day, a night visit like this - during a new Moon, no less - is a rare privilege and I am determined to see what makes this site so special.
Stepping out onto the observing deck at dusk, I watch the four telescope enclosures opening up to the evening air. Their mechanical whispers, groans and sudden rattling of metal gives the distinct impression of giants awakening from slumber.
A copper-red sunset is swiftly followed by the onset of night. It is a truly glorious sky, too packed with stars to properly be called 'dark'. The stars are intense but also eerily unwavering, a fortunate side effect of Pacific winds that blow steadily east along the Tropic of Capricorn and glide over Chile's coastal range with a minimum of turbulence.
In the control room, sensors have determined the 'seeing' tonight to be 0.6 arcseconds - which means the point-like image of a distant star will be blurred by only enough to cover one thirtieth the diameter of a human hair held at arm's length.
For most observatories in the world that is exceptionally good. Here it's about average. (At 4,000 m above sea level, Mauna Kea Observatories in Hawaii can do a bit better, but the higher percentage of cloudy nights there means that overall Paranal is more productive.) It's certainly the best night sky I've ever seen.
At just over a decade old, the VLT is the latest and most sophisticated optical observatory in Chile. It is also the furthest north. This is no coincidence. Now that astronomers are aware of Atacama's great potential there is interest in locating facilities closer to the heart of the region, where clouds are fewer and the air is drier.
This trend is set to continue.
Looking eastward from Paranal at sunrise I can see Cerro Armazones silhouetted against the morning sky. This is a taller mountain and it is easily spotted from the VLT because it pokes up above its neighbours. Chances are good that Armazones will become the new frontier for optical astronomy, and possibly the fullest realisation so far of the Atacama's potential for studying the cosmos.
It is currently one of two sites being considered for the Thirty Metre Telescope (TMT), a massive, segmented-mirror instrument many times larger than any in existence today. If it is not selected for the TMT, then Armazones will almost certainly become home to another great observatory, such as the European Extremely Large Telescope (EELT). (Las Campanas, another Atacama peak, has already been selected as the home for a third observatory of comparable size, the Giant Magellan Telescope (GMT). Whether all three giant telescopes will actually be built remains an open question.)
Meanwhile, an equally exciting future is already taking shape a few hundred kilometres to the northeast on the Chajnantor plain, a broad plateau nestled high within the main range of the Andes Mountains. This is the site of the Atacama Large Millimetre Array (ALMA), the most advanced radio astronomy facility on Earth.
Unlike the VLT, ALMA is not a particularly easy place to visit. It's an active construction site twice as high as Paranal - an elevation that is roughly equal to base camp on Mount Everest and not particularly conducive to clear thinking.
On my journey to Chajnantor I pass a pair of large flatbed trucks crawling up the mountain slope. They are carrying ALMA's first European antenna, a large 12 m dish neatly divided into two semi-parabolic half-shells.
In total, 66 such dishes, provided jointly by Europe, North America and Japan will work in concert to create a sensitive probe of millimetre and submillimetre wavelengths - that part of the electromagnetic spectrum where the far infrared blends into radio.
It is here that astronomers seek to explore a different kind of universe; a universe that is too cool to emit light but warm enough to reveal hidden places like the dusty cocoons where solar systems are born, or the dim awakenings of the first galaxies.
At these wavelengths, says ALMA astronomer Lewis Knee, "water is the enemy." Water molecules absorb photons in the millimetre and submillimetre bands, so even a little moisture in the air renders the sky impenetrable. But the air of the Atacama is dry, especially at an altitude above 5,000 m - above about 95% of what little moisture is present.
There is also another factor, says Knee, that makes this location ideal for ALMA. "Chajnantor offers the rare combination of a site that is high and dry but also fl at, and large enough to spread out." By distributing the array over 12 km, astronomers will gain a higher resolution - roughly 10 times better than the Hubble Space Telescope can achieve.
"That should allow us to see very small details very sharply," says Knee, "so in terms of both resolution and sensitivity, ALMA will be the premier instrument doing this kind of astronomy for the foreseeable future."
There is still a long way to go to make that future a reality. To meet the specifications for ALMA, the individual dishes that make up the array must be the finest parabolas made by human hands. They must also maintain their sensitivity despite strong winds, temperature changes and even the occasional snow storm at high altitude.
Because they are manufactured on different continents by different contractors, the dishes must also be carefully assembled and tested at ALMA's operations facility before being transported up to the plateau (see end of story).
The vision for ALMA is on a scale that dwarfs even the VLT in terms of output. When the antennas are working and signals are being rapidly combined in a device called a 'correlator', ALMA will produce the equivalent of eight DVDs worth of data every second. "All that data will be used to create images of the sky," says Knee.
Meanwhile, other experiments have been taking advantage of ALMA's location to make the kinds of observations not easily done anywhere else on Earth. Not far from where the ALMA control centre is being built, an experiment called the Cosmic Background Imager has been scanning the relic radiation from the Big Bang for years.
Further away, on a distant ridge, the Atacama Cosmology Telescope is performing a similar experiment. Meanwhile astrobiologists have been making use of the Atacama as a testing ground for life detection experiments. Even amateur astronomers are coming to the region to pursue long-term projects or casual stargazing.
For millions of years the Atacama has waited quietly, an empty corner of the planet that later proved to be a treasure chest of mineral wealth. Now a different kind of gold rush is underway. By the time it's over, we are all going to be a lot richer, and a lot closer to the universe.
Mechanic of the VLT
To take advantage of premium sky conditions, the VLT has been outfitted with every trick in the book, making it the most advanced observatory in the world but also one of the most complicated to run. The standard features begin with ‘active optics’, a system of computer-actuated supports upon which each Unit Telescope’s 22-tonne primary mirror rests. When a mirror is over eight metres across but less than 17 cm thick it cannot support its own weight or maintain its precise curvature as the telescope tilts and turns. Active optics solves the problem, continually warping the mirror by just the right amount to keep images sharp.
A second trick is the adaptive optics system, which requires firing a laser into the air above Paranal, creating an ersatz star. Momentto- moment distortions in the laser beam caused by atmospheric turbulence can be read, inverted and applied to a small mirror receiving light from a Unit Telescope. This cleverly cancels out much of the detrimental effect of the turbulence and improves image quality still further.
Finally, on occasion, two telescopes at Paranal can be used in tandem as an ‘interferometer’ – light from both telescopes is combined to achieve the equivalent resolution of a single mirror some 200 m across. In this mode, light from each telescope is passed through a network of tunnels running below the observing deck and processed in a central location.
The basic method is well established in radio astronomy, where long wavelengths make it a relatively easy matter to combine the signals from two antennae. However, it is much harder to achieve in the infrared part of the spectrum, where the VLT’s interferometer operates. Currently, the system can only be used on relatively bright stars. In 2009, astronomers will begin using an enhanced version of the VLT interferometer called PRIMA, which allows for measurements of two sources simultaneously. Among the more exciting applications of such a system would be the direct detection of planets around other stars.
ALMA transporters
How do you move a 115-tonne antennae when you want to fine-tune your brand new radio array? With a custom-built, 28-wheel transporter that is shaped like a horseshoe and can move in any direction. The unusual shape allows the transporter to wrap around an antenna and then lift it up securely before driving it off to its destination. Two such transporters are already at ALMA, where they will be used to move antennae from the assembly and testing facility to the high site for observing. Once there they can be repositioned on various pedestals to change the characteristics of the array to suit different projects.
The transporter can be operated in two modes, one with a driver behind the wheel and another with the driver standing outside the vehicle operating it by remote control – which is quite a disconcerting thing to watch if you’re not used to it!
Atacama for amateurs
During the past generation the Atacama Desert has rapidly become the world’s most enticing location for professional astronomers, but until recently there has been little opportunity for amateur astronomers to partake of the Atacama’s pristine skies.
That is now starting to change, thanks almost single-handedly to Alain Maury, a former professional astronomer and comet discoverer turned galactic entrepreneur. Maury runs San Pedro de Atacama Celestial Explorations (SPACE), a tour and lodge located in the heart of the Atacama that gives casual observers an entertaining introduction to the southern constellations while offering more serious hobbyists a place to bring their telescopes and spend a week or two revelling in the Chilean sky.
“Here, you can be pretty sure that if they come for one week they will have one week of clear weather,” says Maury.
The idea has proved so popular that Maury is expanding into a new area — hosting the remote observatories of serious amateurs who want to station their telescopes permanently in Chile. One current customer is shipping four telescopes to Maury this year to begin a systematic search for extrasolar planets.
Ivan Semeniuk is the journalist-in-residence at the University of Toronto's Dunlop
