A day later, elated astronomers from the European Southern Observatory, a 10-nation consortium that is building the new observatory, marked the event at ESO headquarters in Garching, Germany and at nine other sites in member countries by releasing the first images recorded by the new telescope--the first of four that are being constructed at the site. "Even at this very early stage of evaluation we can state with confidence that the technical performance of the first 8-meter telescope meets or exceeds our expectations in all respects," said ESO General Director Riccardo Giacconi in an address from Garching.
The new telescope at Cerro Paranal is the cornerstone of an ambitious program by European nations to reclaim a leadership in optical astronomy that they held from the time of Galileo. When it is completed in 2003, the four-telescope array, known as the VLT (for Very Large Telescope), will comprise the world's most powerful ground based optical and infrared observatory. Its ability to resolve distant objects will rival--and sometimes exceed--telescopes in space, such as the U.S. Hubble Space Telescope. "For Europe this marks the realization for the first time in this century of a facility for ground based optical and infrared astronomy which equals or surpasses any available in the world," Giacconi said.
Planning for the VLT began in the late 1970s and the project moved into full swing in December 1987. The final step in preparing the first unit was the application of a thin coating of aluminum on the mirror, measuring 8.2 meters in diameter. The only larger mirror is the 10-meter telescope at the U.S. Keck Observatory on Mauna Kea, Hawaii. The coating operation, in a huge vacuum chamber, was completed at Paranal on May 20 and the mirror was installed in the telescope housing on May 21. A series of tests on the instrument's tracking and resolving ability were conducted over the next four days, leading up to the First Light on May 25.
The planned observatory incorporates advanced technology that will make it the most sophisticated ever built. The main glass mirrors, cast according to a thin honeycomb design, rest on a system of 150 computer-controlled actuators that can bend them slightly to induce precise distortions. This system, known as active optics, allows operators to adjust the lens to compensate for aberrations that would distort images. A second set of smaller mirrors--which reflect the light to viewing and recording instruments--is also computer controlled.
Astronomers will be able to combine the light from the four telescopes, once completed, into a single image, producing the equivalent of a telescope with a mirror 16 meters in diameter. And they have still another trick up their sleeves; the telescope array is designed to function as an interferometer--a device that combines the wave patterns of light from the various telescopes. A number of such projects, believed to be the cutting edge of optical astronomy, are underway around the world.