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May 28, 2023


All about GTC

Once upon a time...

The site

The GTC is being built on an area of 5,000 m² at the Observatorio del Roque de los Muchachos (ORM), on the island of La Palma in the Canaries. The Observatory is on the edge of the Caldera de Taburiente National Park, in the municipality of Garafía, 2,400 m above sea level on top of the ‘sea of clouds’. It is an ideal site for astrophysics thanks to the clear, stable atmosphere produced by the Trade Winds. Here, geography and climate combine to give exceptional conditions for astronomical observation, which is why the Observatory is home to one of the most extensive fleets of telescopes to be found anywhere in the world. It is also one of the most extensively researched observing sites – continuous site testing campaigns are undertaken to systematically analyse the clarity and consistency of the atmosphere, thereby guaranteeing high quality observing.

The Observatory only became a reality, though, at the end of a long hard road of work and research.

The modern history of astronomy in the Canaries begins with the astronomical expeditions of the XIX century. In 1856, the British astronomer Piazzi Smyth verified Newton’s claim that high altitude locations were best for astronomical observation. Piazzy Smyth reached this conclusion after observing from different altitudes in Tenerife, ranging from sea-level to Guajara (2,717 m above sea level) and Altavista (3,250 m), just beneath the summit of Mount Teide. Then in 1910 the French astronomer Jean Mascart travelled to the Canaries to observe Halley’s Comet. So impressed was he by the potential for observation offered by Tenerife’s peaks that he put forward plans for an international observatory at Guajara. Everything ground to a halt, though, with the advent of World War One.

In 1959 astronomers from all over the world were back in the Islands to observe a solar eclipse. Interest in creating a permanent observatory was rekindled. Prompted by the demand from the worlds of astronomy and astrophysics, Spain took the first firm steps to set up an astrophysical observatory in Tenerife. It was not long before the excellent conditions the area had to offer for this kind of research had been proven and the first Spanish astrophysics group was getting off the ground. The 1960s saw the first systematic site testing in Tenerife and in 1970 Observatorio del Teide (OT) was inaugurated, under the auspices of the University of La Laguna.

In 1964 Bordeaux Observatory built a photoelectric telescopeat Izaña (OT). Then, at the start of the 1970s, a solar telescope was added, to be joined soon after, in 1972, by a 1.5 m infrared telescope known today as the Carlos Sanchez Telescope.

With the virtues of the Canarian skies for astronomical observation now proven, the construction of Observatorio del Roque de los Muchachos got underway in the 1970s. 

After negotiating with a number of European scientific institutions interested in setting up telescopes in the Canaries, the Observatory opened its doors to international participation in 1979 when the Agreements on Cooperation in Astrophysics, which regulate the use of the sky in the Canaries, were signed.

The Observatorio del Roque de los Muchachos (inaugurated in 1985) and the Observatorio del Teide belong to the Instituto de Astrofísica de Canarias, which has its headquarters at the Instituto de Astrofísica of University of La Laguna. Together, they form the European Northern Observatory (ENO).


Modern civilisation has brought many advances but some of its effects can get in the way of observation if they are not properly controlled. Excessive light – or light pollution – from towns and cities is one such drawback, as are radio and electrical interference, flight paths and atmospheric pollution. Since 1988 they have been controlled by the ‘Sky Law’ in the Canaries – a set of regulations that protect the quality of observation for the Observatories. The IAC’s Sky Quality Protection Unit (OTCP), ensures adherence to the law, and its Sky Quality Group, continuously monitors the parameters that define observing quality at the IAC Observatories.