We have looked previously on the history and design of telescopes. But what goes into planning for a new observatory and telescope site? What sites are the best in the world and why do they hold that title?
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The locations for telescope observatories need to be carefully considered, especially when you are pouring millions to billions of dollars into building a world-class telescope.
There are some obvious requirements such as it should be built where there is a dark sky. This is why so many observatories lie away from big cities, or out in the middle of nowhere. Mt Stromlo Observatory and many other old observatories such as Griffith Observatory in the US are in unique positions where they used to be great observing sites, but due to the expansion of nearby cities (Canberra for Mt Stromlo and Los Angeles for Griffith), the skies are no longer as dark due to light pollution. This is the main factor in why Mt Stromlo did not rebuild any research grade telescopes after the fires in 2003. Instead, new telescopes were built at its sister Siding Spring Observatory near Coonabarrabran, NSW.
Along with a dark sky, astronomers care a lot about the weather - the less cloudy or wet nights, the more time you can spend observing. That's why many observatories are located high up in deserts. The high altitude and dry conditions mean that your telescope can observe many more nights than if you built your telescope in a rainforest.
Being at a high altitude has another advantage as well: less atmosphere. The atmosphere is an observational astronomer's worst enemy, as winds and temperature gradients in the atmosphere cause light from stars and galaxies to get jumbled up and blurred on a camera. This is why stars twinkle at night.
While we can use techniques such as adaptive optics to reduce the effect of the atmosphere, it is best to try and minimise the amount of atmosphere from the outset. So, putting your observatory on a mountain reduces the amount of atmosphere the light has to travel through.
Perhaps the best astronomy sites in the world are located in the Atacama Desert of northern Chile. These sites, such as Paranal Observatory, tick the list of being very high (2500-5000m), very dry (the second driest place on Earth), away from light pollution, and are not dreadfully inaccessible to reach.
The island of Hawaii and the Canary Islands off the coast of Morocco are also fantastic observatory sites.
There is one last location that is fantastic for astronomy: the driest and most isolated place in the world, Antarctica.
Some of the mountains of Antarctica, such as Dome A and Dome C, are even perhaps the best places for astronomy in the world in terms of how clear the night sky is.
The problem with Antarctic observatories, though, is how inaccessible Antarctica is, as well as managing the effects of the extreme cold on your telescopes.
- Jonah Hansen is a PhD student specialising in space interferometry at Mount Stromlo Observatory, at the Australian National University.
