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A visit to the world's largest optical telescope

Paul Sutherland, Feature writer
Sep 24, 2012, 7:00 UTC

Sen—High on a crater's edge on the volcanic Canary Island of La Palma is perched one of the world's major astronomical observatories. It includes the largest optical telescope on the planet. Sen paid a visit.

Called the Observatorio del Roque de los Muchachos (ORM), the many telescopes could hardly have a more dramatic setting. At a height of 2,396 metres above sea level, and a latitude of 28° 45' north, they are Europe's most important observing facility in the northern hemisphere.

They complement the various telescopes of the southern hemisphere operated by the European Southern Observatory (ESO) in Chile and are only rivalled for importance in the northern hemisphere by the array of telescopes on Hawaii, half a world away.

This writer had a special interest in seeing the La Palma observatory again, for the first time since the 1980s, because he was one of a small band of hardy young men who tested the Canarian skies 40 years ago when the observatory was being planned.

Though I was based on the larger nearby island of Tenerife, I recall sailing over with our Land Rover to "la isla bonita" as La Palma is known in 1972 to help pack up tents that had been used by a breakaway group up at the Roque de los Muchachos (literally the rock of the chums) on the edge of a vast collapsed crater that is the Caldera de Taburiente National Park.

La Palma is said to be the steepest inhabited island in the world. We had to walk with mules for three hours to reach a desolate summit. But within ten years, a new road had been driven to the top and the first instrument, the 2.5-metre Isaac Newton Telescope, moved there from its previous home in East Sussex, England, to begin operating in 1984.

A number of European nations supported the opening of the observatory, operated by the Canaries Astrophysics Institute (IAC), and many heads of state and other dignitaries flew to the inaugural ceremony, hosted by the King and Queen of Spain in 1985.

Grantecan - world's biggest optical telescope

The GranTeCan telescope dome, left, and a fish-eye view of the instrument itself. Credit: Paul Sutherland

Two years later, in 1987, a larger instrument, the William Herschel Telescope with a 4.2-metre mirror was opened close by. This was the biggest at the observatory for many years, and one of the largest in the world, playing an important part in the 1990s in confirming the acceleration of the expansion of the Universe. But it lost its crown in 2008 when the Spanish-led Gran Telescopio Canarias, also known as GranTeCan, or the GTC, turned its segmented 10.4-metre eye on the sky.

Mexico and the University of Florida are also partners in GranTeCan which is likely to remain the world's biggest optical telescope until ESO has final approval and funds to build the European Extremely Large Telescope at Cerro Armazones in Chile.

Paul Sutherland on La Palma

Sen writer Paul Sutherland with the telescopes on La Palma. Credit: Paul Sutherland

Other instruments at the ORM include the giant open-air MAGIC, a 17-metre instrument for detecting Cherenkov radiation from gamma rays, 3.5-metre Telescopio Nazionale Galileo, 2.56-metre Nordic Optical Telescope, 2-metre robotic Liverpool Telescope which is controlled over the Internet, and 1-metre Swedish Solar Telescope.

The La Palma island government has strongly supported the observatory by controlling lighting on the island as well as aircraft routes in the locality to protect the quality of the sky.

By the way, my visit to the island this time (my fourth) to attend the annual conference of the International Meteor Organization was made a lot more comfortable than that first trek thanks to the support of the La Palma government, or Cabildo, aided by the conference's commercial organisers Astro Travels. Many thanks to them!