Telescopes orbiting Earth can peer billions of light-years into space to observe incredible phenomena across the cosmos. But to push the boundaries of astronomy while planted solidly on the ground, Earth-bound observatories tend to be among the most extreme scientific facilities on the planet.
1. Atacama Large Millimeter/submillimeter Array (ALMA)
This radio astronomy telescope represents an unprecedented partnership between Europe, North America, East Asia, and the Republic of Chile. When fully built in 2013, the finished facility will sport 66 antennas sprouting from the high, dry Chajnantor Plateau, at an altitude of 16,400 feet (5,000 meters). "It's a tough place to work," said Phil Puxley, of the National Science Foundation. "The air pressure there is almost 50 percent that at sea level, so some people refer to it jokingly as 'halfway to space.'"
ALMA's antennas work together to scan the sky at millimeter and submillimeter wavelengths, observing the oldest galaxies as well as baby planets just beginning to form around young stars. ALMA's full power will surpass previous submillimeter instruments by factors of ten to a hundred in areas such as field of view, sensitivity, and resolution. "It's a bigger jump than Hubble was over any existing ground telescope," Puxley said. "And when we think of Hubble's incredible results, it's hard to imagine what will come out of ALMA."
2. Gran Telescopio Canarias
Boasting a massive 34-foot-wide (10.4-meter-wide) segmented mirror, the Gran Telescopio Canarias is currently the largest optical-infrared telescope in the world. The enormous telescope is perched high atop a volcanic peak on La Palma, in the Spanish-run Canary Islands, where skies are dark and observation conditions are ideal. In fact, the remote and dizzying locale created a few construction difficulties, and it took seven years of hard work before the telescope captured its first light in July 2007.
The GTC is co-owned by the government of Spain, two Mexican institutes, and the University of Florida. The instrument is able to search out some of the most distant and faintest objects in the universe, allowing astronomers to observe the birth of new stars, the characteristics of black holes, and even some of the primordial chemical remnants of the big bang.
3. South Pole Telescope
The South Pole Telescope sits on a miles-thick ice sheet at a dizzying altitude of almost 10,000 feet (3,000 meters). Winter temperatures can dip to -100 degrees Fahrenheit (-73 degrees Celsius), and the facility sits 11 hours by plane from the closest city. Astronomers use a single word to describe these conditions: perfect.
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The telescope is used to study the cosmic microwave background (CMB), the afterglow of primordial light from the big bang 13.7 billion years ago. This faint radiation is mostly blocked by water vapor in our atmosphere, but the Pole's cold, dry conditions open a window on the CMB, helping astronomers learn more about the age and evolution of our universe, and perhaps even allowing them to one day unlock the secrets of dark energy-the mysterious force believed to be driving the universe's accelerated expansion.
4. Super-Kamiokande Neutrino Observatory
Unlike most observatories perched on high peaks, Japan's Super-K observatory lies more than half a mile (a thousand meters) under a mountain. The seemingly odd location, far below Japan's Mount Kamioka, is a function of the telescope's unusual mission: the search for neutrinos-small, uncharged particles born in nuclear reactions, such as those inside stars. Neutrinos are hard to spot because they're usually overwhelmed by background radiation, and because the particles can pass through most matter without a trace. For instance, more than 50 trillion neutrinos from the sun passed through your body during the time it took to read this sentence.
To detect such ghostly particles, Super-K was built far enough underground to isolate its detectors from background noise. The facility contains a large, stainless steel tank filled with ultrapure water, and the chamber is lined with glass tubes that can detect the unique kind of radiation created when a neutrino does interact with the water's subatomic particles. Super-K allows astronomers to measure neutrinos and trace where they came from, offering clues to what happens inside stars, how stellar giants explode as supernovae, and even how the first matter in the universe was created.
5. Arecibo Observatory
The world's largest and most sensitive single-dish radio telescope is big-very, very big. The dish covers nearly 20 acres (8 hectares) and is so massive that it was built into the ground near Arecibo, Puerto Rico, so that it wouldn't collapse under its own weight.
Arceibo excels at gathering data on pulsars, rapidly rotating neutron stars that seem to emit pulses of optical, x-ray, and gamma-ray light. The huge dish allows astronomers to time these stars' pulse rates with extreme precision, NSF's Puxley said. "Using them as a reference clock, you can do some very important physics experiments, like measuring the state of the matter inside a neutron star-something that's very hard to conceive of being able to do," he said. "You can even measure the pulsar itself and make tests of the theory of general relativity in the very strong gravitational environment you get when you collapse the mass of a star down to a radius of just ten kilometers [six miles] or so."
6. Gemini South
The twin Gemini telescopes, one in Hawaii and one in Chile, are powerful optical-infrared instruments that together can observe the entire night sky. At Gemini South, on an Andes mountaintop called Cerro Pachon, an adaptive-optics system supercharges the capabilities of the telescope's massive 26-foot (8-meter) mirror, the better to study black holes or the evolution of distant stars, NSF's Puxley said.
In adaptive optics, telescope operators "shine a laser into the sky next to the telescope and observe that laser light entering the atmosphere's sodium layer at 90 kilometers (56 miles)," Puxley explained. "Then they can use the light emitted back from that spot to correct the optics of the 'scope in real time for the turbulence in the atmosphere." Instead of using just one laser to correct a small region of the sky, Gemini South uses five guide lasers, arranged like the dots on a die, to correct the telescope's entire field of view. That means Gemini South observes an area of the night sky ten times bigger than that of any other adaptive-optics system in the world.
7. McMath-Pierce Solar Telescope
The McMath-Pierce Solar Telescoe, on Kitt Peak in Arizona, is the biggest solar telescope in the world, helping astronomers keep a close watch on the nearest star to Earth.
The massive telescope looks a bit like an enclosed ski jump, with a 100-foot (30-meter) tower holding up one end of a slanted, 200-foot-long (61-meter-long) instrument that extends into the side of the mountain. Sunlight is reflected into the tunnel-like shaft by a three-mirror device called a heliostat, providing astronomers with a safe look at solar flares, sunspots, and other features of our stormy star. The telescope does double duty at night, allowing astronomers to observe more distant celestial bodies.
8. Very Large Telescope
The European Southern Observatory bills its Very Large Telescope array as the world's most advanced optical instrument. Each of the four Unit telescopes, boasting mirrors 27 feet (8.2 meters) wide, can spot objects four billion times fainter than humans can see with the naked eye. But the real showstopper is when data from the Unit dishes is blended with information from four smaller auxiliary telescopes. The resulting VLT interferometer can reconstruct images with an angular resolution measured in milliarseconds-the equivalent of a human being able to distinguish a pair of automobile headlights on the moon.
From northern Chile's Atacama Desert, the VLT has so far produced one of the first direct images of a planet outside the solar system, spotted the afterglow of the farthest known gamma-ray burst, and tracked the movements of individual stars swirling around the supermassive black hole at the center of our Milky Way galaxy.
9. Karl G. Jansky Very Large Array
In 2011 engineers completed an operational facelift of the National Radio Astronomy Observatory's Very Large Array, which has been in operation for more than 30 years. "What's happened over the last several years is a refurbishment to refit the antennas with a new suite of receivers and electronics that really has improved its capability by an order of magnitude," NSF's Puxley said. "It's a new take on an old, cherished observatory."
The famed astronomical radio observatory sits about 50 miles (80 kilometers) west of Socorro, New Mexico, and boasts 27 large antennas configured in a "Y" shape. When the power of each dish is combined, the array boasts the sensitivity of a single dish 422 feet (130 meters) wide.
10. Magdalena Ridge Observatory Interferometer (MROI)
This mountaintop telescope array sits at 10,600 feet (3,230 meters), but it's not the altitude that makes Magdalena Ridge extreme. Ten 4.6-foot (1.4-meter) telescopes-which are being assembled and will come online in late 2012-will be linked together to create the equivalent of a single telescope 1,115 feet (340 meters) wide.
The system will help scientists see objects with a hundred times the resolution of the Hubble Space Telescope-from a New Mexico mountaintop. The interferometer will target the kind of faint astrophysics phenomena that are usually measured only indirectly to explore models for active supermassive black holes, the evolution of stars, and the signatures of planet formation
