Tuesday, January 28, 2014

Dry Desert and Clear Skies

Norte Chico, Chile (January 8, 2006)

We live at the bottom of a turbulent ocean, an ocean of air that we call atmosphere. It is a thin layer, if we look at it from space: an almost impalpable skin. Still, for all creatures living at the bottom of this sea, it is a nurturing elixir, our sustenance, the source of life. For us astronomers, however, is more like a scourge!

Let me qualify. It is not that we astronomers don't like to breathe, that's not the issue. The problem is that this turbulent ocean is, well, turbulent. It is like looking up from the bottom of a swimming pool: you can still see the lifeguard looking down from the side of the pool, but she is all blurred. You would never tell that she has that concerned face as she is trying to figure out what the hell are you doing at the bottom, until she jumps in and pulls you out and your pool card is revoked. Crap! It is the same with the atmosphere, it blurs and distorts the light coming from the stars, making our billion-dollar telescopes worthless (well, almost). And that's not even all of it: even in crystal-clear days the sky is not really transparent: the pesky molecules that makes up our air are very selective about the color of the light they allow to pass through. In the visible range, the one the human eye can see, it is not so bad. But go slightly redder or slightly bluer (we have nice CCD detectors for that) and the atmosphere becomes increasingly opaque. The main culprits for this are some notorious molecules we all know about: water vapor, ozone and CO2. These molecules are particularly nasty in the infrared and microwave range: this is not surprising since they are powerful greenhouse gasses. They let Sun's radiation in, but don't allow the thermal infrared radiation from the ground to escape back to space. The heat is trapped and the poor planet overheats. If you are a climatologist, you should be concerned about CO2, which of these three molecules is the one we are artificially messing up to level not seen in millions of years. If you are an astronomers, however, your enemy is water. If you want to see the infrared stars you need to find the place with the least amount of water vapors on top of your head. Hence astronomers quest for dry high mountain deserts.

This is what northern Chile offers to astronomers. A dry highland desert with little or no precipitations, and a very dry air that is as transparent as it gets without leaving the atmosphere altogether and launch your telescope to space. The Las Campanas observatory is at the edge of the largest of the Chilean dry highlands: the Atacama desert. You can see the views in the photos of this post: rocks, sands and a sturdy fauna and flora perfectly adapted to an environment where it may not rain for years: an astronomer's dream, and a beautiful muse for a photographer looking for unadulterated landscapes of the nude Earth.

Norte Chico, Chile (January 8, 2006)


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