European Southern Observatory

European Southern Observatory (ESO), an intergovernmental organization for astronomical research with headquarters in Garching, near Munich, Germany. The ESO began in 1962 as a consortium among Belgium, Denmark, France, Germany, the Netherlands, and Sweden. Great Britain, Italy, Portugal, and Sweden subsequently joined. The ESO operates two major observatories in the Atacama desert, Chile.

The older observatory, inaugurated in 1969, is located on Cerro La Silla at an altitude of about 8,000 ft (2,400 m). The initial instrument was a 3.6-m (142-in.) reflecting telescope, but in 1989 the 3.58-m (141-in.) New Technology Telescope (NTT) was installed. Its primary mirror is three times faster than the 3.6-m and has only half its weight. It uses a principle called active optics, in which the optics are adjusted by computer to react to the changing seeing conditions of the night sky. Other instruments include a 2.2-m (86.6-in.) reflector, a 0.5-m (20-in.) reflector, a 1-m (39.4-in.) Schmidt camera telescope, twin 0.4-m (15.7-in.) astrographic telescopes, a 1.52-m (60-in.) spectrographic reflector, and a 1-m (39.4-in.) photometric reflector. Also located at Cerro La Silla are a 0.5-m (20-in.) reflector belonging to Denmark and a 0.62-m (24.4-in.) reflector belonging to the Univ. of Bochum, Germany.

The second observatory, initiated in 1988 and inaugurated in 1999, is located atop Cerro Paranal at an altitude of about 8,640 ft (2,635 m). The observatory is the home of the Very Large Telescope (VLT) program. Begun in 1996, it links four 315-in. (8-m) telescopes together with several movable 72-in. (1.8-m) telescopes through optical interferometry, a technique in which the signals from each telescope enhance the signals from the others. Completed in 2003, the combination produces a virtual telescope image equivalent to that of a 630-in. (16-m) conventional reflecting telescope.

Among the other programs of the observatory is the completion of the photographic Sky Survey for the Southern Hemisphere, in cooperation with the Siding Spring Observatory in Australia. This project is a continuation of the work begun in the Northern Hemisphere with the Schmidt telescope at Palomar Observatory.