Starwatch: The European Extremely Large Telescope

Alan Pickup on the world's largest optical telescopes, and the new European one to be built in the Andes that will revolutionise astronomy

Our image shows an artist's impression of the European Extremely Large Telescope, or E-ELT, whose 39-metre aperture puts it in line to be the world's largest optical-infrared telescope. Being built by the European Southern Observatory, it will cost in excess of 1bn euros, including a British contribution of £88m. Explosions began in June to create a level home for it atop the 3000-metre peak of Cerro Armazones in the Chilean Andes, overlooking the Atacama Desert.

It could be another ten years before the E-ELT is fully operational. By then, the Thirty Metre Telescope (TMT), may have seized the crown. albeit temporarily, as the world's biggest. Built by a US-led consortium that includes India, China and Japan, work to place it on Mauna Kea in Hawaii should begin this summer.

For almost three decades from its completion in 1948, the 200-inch Hale telescope on Mount Palomar, California, was the largest telescope. Its single mirror, 200 inches or 5.08 metres, in diameter, was unrivalled in light-collecting area until the Soviet 6.0-metre BTA telescope on the Caucasus mountains saw its first light in 1975. Sadly this was bedevilled by structural and observing-site problems from the start, but it remained the largest until the first of the two 10-metre Keck telescopes came into operation on Mauna Kea in 1993.

The 10.4-metre and largely Spanish-operated Gran Telescopio Canarias, on the Canary Island of La Palma, has headed the pack since 2006. This and the Kecks use segmented mirrors in which the aperture is filled with an array of smaller computer-controlled mirrors. The new super-telescopes will use segmented mirrors, too, with a total of 798 hexagonal segments for the E-ELT and 492 for the TMT.

The observing locations are also critical. The sites in Chile and Hawaii are clear on most nights of the year, with near-perfect "seeing" and negligible interference from artificial lighting. They are also extremely arid with scarcely a hint of water vapour to absorb infrared wavelengths.

It seems inevitable that the size and power of the E-ELT will revolutionise astronomy. It should, for example, allow rocky planets of other stars to be imaged for the first time and for their atmospheres to be analysed. While the ultimate aim may be to glimpse signs of alien life, it is more realistic to expect that it will be able to characterise the planetary systems of other stars, and how they form and evolve.

It should also give us our sharpest views yet of the earliest stars and galaxies, those born only a few million years after the big bang, and how interactions and mergers over the aeons have led to the universe we see today. There must be countless other discoveries awaiting and, undoubtedly, new mysteries identified that we cannot yet imagine.


Alan Pickup

The GuardianTramp

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