Why Chile will host the Extremely Large Telescope
The European Southern Observatory (ESO) has chosen Chile as the site for it’s next generation telescope: the 42-metre E-ELT (European Extremely Large Telescope).
The E-ELT will be built on Cerro Armazones, a 3060-metre-high mountain, about 20 kilometres from Cerro Paranal, which hosts ESO’s Very Large Telescope.
These mountains are about a 2 hour drive from the coastal town of Antofagasta. The reasons why ESO chose Cerro Paranal are exactly why they chose Cerro Armazones. There are some unique climactic conditions that make the region great for astronomy.
These mountains are in the Atacama Desert, one of the driest regions of the world. It lies on the leeward side of the Andes, which act as a formidable barrier to the moisture-laden winds from the east. Some parts of the desert haven’t seen rain for years; some haven’t seen any in recent memory. Couple the dryness with the desert’s high altitude and the stillness of the air above it and you have some of the best “seeing,” as astronomers say, in the world. There’s little of the atmospheric turbulence that haunts even the best of telescopes.
Cerro Paranal is a 2,635-meter-high mountain in the Atacama Desert, about 120 kilometers south of Antofagasta and barely 12 kilometers inland from the Pacific coast. Despite a clear line of sight, the ocean is rarely seen from the mountain, as it is often obscured by a thick layer of clouds, the kind you would normally see from an airplane at 40,000 feet. These low-lying clouds are exactly what make Cerro Paranal (and hence Cerro Armazones) a perfect spot for astronomy. The cold Humboldt Current, flowing northward along the Chilean coast, creates a strong inversion layer, pulling the clouds down to well below the summit of Paranal, not just reducing the moisture in the air around its telescopes but also creating nearly 350 days of clear skies. The dry air above Paranal—low in water vapor—allows light from outer space to reach the telescopes without being absorbed by the atmosphere. Nowhere else on Earth do these climatic features—a high-altitude desert and an ocean-induced inversion layer—come together as they do in the Atacama.