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The Paranal Metamorphosis

From Mountain Top to Top Observatory

20 de Diciembre de 2000

Some years ago, the Paranal mountain was still a remote and inhospitable site, some 12 km from the Pacific Coast in the dry Atacama desert in northern Chile. Few aircraft passengers flying along that coast would notice anything particular about this peak, except perhaps that it was one of the tallest in the steep coastal mountain range. Already in the early 1960's, pioneer astronomers crossed this desolate region in search of suitable sites for future observatories. One of them, Jürgen Stock, did notice the Paranal peak as a possible candidate. However, without any water in this extremely dry area, how could any people, even hardy scientists, ever live up there? He then went on to discover La Silla, where ESO decided to build its first observatory in 1964.

ESO presence at Paranal from 1983

In the beginning of the 1980's, when the main construction phase at La Silla was over, ESO launched a thorough search for the best possible site for the next-generation telescope, already then known as the "Very Large Telescope", or VLT. During this campaign, the Paranal mountain was visited by a small search troupe from this organisation, including the ESO Director General (1975 - 1987), Lo Woltjer . The first test measurements indicated a great potential for astronomical observations, both in term of clear nights and low humidity, the latter being particularly important for infrared observations.

From 1983, ESO maintained a small site testing station at the top of Paranal. The meteorological conditions were registered around the clock and the atmospheric transparency and stability were recorded each night. At that time, the mountain Vizcachas, a site near ESO's first observatory, La Silla, and some 600 km further south, was also considered a possible site for the VLT. The data from the two sites were therefore carefully compared over a period of several years.

Paranal becomes the site for the VLT

Following the decision in December 1987 by the ESO Council to embark upon the VLT Project (with Massimo Tarenghi as Project Manager), Paranal was chosen as the site in 1991. In the meantime, the Chilean Government had resolved to donate an area of approx. 700 km 2 around this mountain to ESO, and construction work started the same year. The left photo shows Paranal at this stage.

The development of Paranal included much blasting and heavy earthwork; about 350,000 m 3 of rock had to be moved to achieve a flat platform of sufficient size to house the various components of the VLT and, in particular, the spacious VLT Interferometer. The situation, right after this work, is depicted in the middle photo from 1994.

An operational observatory

The construction at Paranal progressed at high speed. It is hard to believe that just four years later, "First Light" was achieved with the first 8.2-m telescope, ANTU, in May 1998. Then followed KUEYEN (March 1999), MELIPAL (January 2000) and YEPUN (September 2000).

The first two telescopes have now been "taken over" by the astronomers and Paranal has become an operational observatory with Roberto Gilmozzi as Director. Large numbers of scientists in the ESO member countries, and even more within international collaborations, are busy producing exciting research results, now increasingly visible in the world's professional journals and some of which are announced in the ESO Press Releases.

The other two will soon be equipped with high-quality astronomical instruments; the first will be VIMOS at MELIPAL in the beginning of 2001. Both telescopes will become fully available to the astronomical community in the course of 2001.

And now the VLT Interferometer...

The next decisive step will happen already in early 2001, when the VLT Interferometer is expected to see "First Fringes", the equivalent of "First Light" for this type of facility.

This is when two small "siderostats" on the Paranal platform will track and capture the light from one and the same (bright) star, directing the two beams towards the underground Interferometric Laboratory via a series of intermediate mirrors.

Here, the critical technical elements are the "delay lines" in the Interferometric Tunnel. They have already undergone the first tests with very positive results, so the ESO staff is in a confident mood.

Later in 2001, two of the 8.2-m Unit Telescopes will be coupled and interferometric test observations will be made on faint celestial objects. In the next years, the three movable 1.8-m Auxiliary Telescopes will be installed on the Paranal "railroad" and the VLT Interferometer will progressively enter into full operation.

From a lonely mountain top to the world's foremost optical/infrared astronomical observatory, Paranal has indeed come a long way!

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