Prime real estate for astronomy

Cordon Macon, a candidate site of the E-ELT

Cordon Macon, a candidate site of the E-ELT

I recently spotted this great image on the ESO website, where it was “ESO Chile Image of the Month” a while ago.  It’s an eastward view over Cordon Macon, located in the Argentinian province of Salta and one of the candidate sites for the European Extremely Large Telescope, or E-ELT. The equipment used for monitoring of the site is just a tiny speck on the ridge, shown enlarged in the inset.

The ESO-led E-ELT project is one of a number of observatories under development worldwide for the optical and infrared that will enable astronomers to take a giant leap in our understanding of the Universe. With its primary mirror measuring 42 m in diameter, it will smash the size record for optical telescopes, which currently stands around 10 m, in spectacular fashion. When this giant light bucket comes online around 2018 we’ll be able to collect and analyse the sparse photons from the most distant corners of the Universe, the faintest exoplanets and the smallest objects in our own Solar System.

Location is of crucial importance: to get the scientific return from such a mammoth telescope, observing conditions have to be optimal at all times. Dark and clear skies and little atmospheric turbulence are essential for the E-ELT to reach its peak resolution and sensitivity. This is the reason today’s telescopes are found in very strange and exotic locations you may associate more with James Bond films than science.

The amount of water in the atmosphere, which tends to decline strongly with height above sea level, is also important as it will dictate how much infrared light can be spotted by the E-ELT. While observing in the infrared is not so fundamentally different from the optical, infrared radiation is absorbed by water molecules in the atmosphere at particular wavelengths. This creates just a number of infrared “windows” that are open to observers from the ground. A very dry site can open up gaps in the windows that would otherwise we blocked by the atmosphere.

ESO are currently undertaking an intensive site testing campaign at a  number of candidate sites around the world for their flagship optical telescope for the next decade. While scientists’ careful measurements over many months of the temperature, wind and turbulence profiles are a powerful driver for the final choice of site, politics also play an important part.  Will the government of the country allow an international organisation to purchase the land and develop it for astronomy? What will they want in return? Is there support from the local (often indigenous) population? Is the area politically stable? Who owns the mining concessions in the area? All these questions need to be addressed before a final decision is made – and that means tons of careful negotiating and diplomacy!

I think I’ll stick to dreaming about my first visit, wherever it is (and helping design one if its instruments).

Image credit: Gianluca Lombardi, 2008.

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