The European Southern Observatory (ESO) is an intergovernmental astronomy organization in Europe. Headquartered in Garching, Germany, ESO has 16 member states. These are Austria, Belgium, the Czech Republic, Denmark, Finland, France, Germany, Italy, the Netherlands, Poland, Portugal (including the Azores and Madeira), Spain (including the Canary Islands), Sweden and Switzerland. Chile is also a cooperating state of ESO. By convention astronomers use two systems to refer to objects in space: celestial coordinate system such as right ascension and declination; and equatorial coordinates such as longitude and latitude. The location of ESO’s La Silla Observatory at 29°15′ South latitude means that it can only observe objects above that declination — i.e., all objects north of La Silla appear upside down when seen from Chile!
ESO’s primary mirror at the Very Large Telescope on Cerro Paranal is an array of four mirrors each 8.2 m across; these combine to give a collecting area of about 128 m2 — one of the largest single optical telescopes currently in operation. It uses a fifth smaller auxiliary mirror to deliver light into its various instruments.
ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At 3200 metres above sea level on Cerro Paranal in the Atacama Desert — one of the driest places on Earth — ESO has built what is widely regarded as the most advanced astronomical observatory in existence: The Very Large Telescope Array (VLTA).
At 5000 metres above sea level on Llano de Chajnantor in northern Chile — one of the highest astronomical observation sites on Earth — ESO’s APEX telescope is probing cosmic mysteries with far-infrared eyesight better than ever before from ground-based facilities. Located close to APEX are ALMA antennas which form an array with up to 66 units providing unprecedented views of our Universe during construction phase which will be completed around 2013 .
La Silla was ESO’s first observatory site and remains home to several important telescopes including HARPS which has discovered more than 130 planets outside our Solar System since 2004 using the radial velocity method . In May 2009 , ESA’s Herschel Space Observatory was launched from Kourou atop an Ariane 5 rocket together with Planck , another ESA mission . After a journey lasting almost 30 minutes , Herschel separated successfully from Planck and continued its 696 million kilometre trip towards L2 , 1½ million kilometres beyond Earth . Just under four hours later , Herschel entered safe mode due presumably to high temperatures near its sunshield ; following intervention by ground controllers , normal operations resumed on 13 May .