ESO Observing Facilities

As set out in its convention, ESO provides state of the art facilities for Europe's astronomers and promotes and organises cooperation in astronomical research. Today, ESO operates the La Silla Paranal Observatory, providing some of the world's largest and most advanced observational facilities at three sites in Northern Chile: La Silla, Paranal and Chajnantor. These are the best locations known in the southern hemisphere for astronomical observations.


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The Very Large Telescope (VLT) at Cerro Paranal is ESO's premier site for observations in the visible and infrared light. All four unit telescopes of 8.2-m diameter are individually in operation with a large collection of instruments.

The VLT offers also the possibility of combining coherently the light from the four UTs to work as an interferometer. The Very Large Telescope Interferometer (VLTI), with its own suite of instruments, ultimately providing imagery at the milli arcsecond level as well as astrometry at 10 micro arcsecond precision. In addition to the 8.2m diameter telescopes the VLTI is complemented with four Auxiliary Telescopes (AT) of 1.8m diameter to improve its imaging capabilities and enable full nighttime use on a year-round basis.

La Silla

ESO operates two major telescopes (3.6m telescope, New Technology Telescope (NTT)) at La Silla. They are equipped with state of the art instruments either built completely by ESO or by external consortia, with substantial contribution by ESO.


APEX, the Atacama Pathfinder Experiment, is a collaboration between Max Planck Institut für Radioastronomie (MPIfR) at 50%, Onsala Space Observatory (OSO) at 23%, and ESO at 27% to construct and operate a modified ALMA prototype antenna as a single dish on the high altitude site of Llano Chajnantor. The telescope was supplied by VERTEX Antennentechnik in Duisburg, Germany.


The ALMA project is an international collaboration between Europe, East Asia and North America in cooperation with the Republic of Chile. It is coordinated and operated by the Joint ALMA Observatory (JAO) in Chile on behalf of the three executives. The European executive is represented by ESO, which also hosts the European ALMA Regional Centre. The other partners North America and East Asia are represented by NRAO and NAOJ respectively.