Atacama Pathfinder Experiment

Atacama Pathfinder Experiment

The APEX telescope
Alternative names	APEX
Part of	Event Horizon Telescope Llano de Chajnantor Observatory
Location(s)	Atacama Desert
Coordinates	23°00′21″S 67°45′33″W / 23.0058°S 67.7592°W / -23.0058; -67.7592Coordinates: 23°00′21″S 67°45′33″W / 23.0058°S 67.7592°W / -23.0058; -67.7592
Organization	European Southern Observatory Max Planck Institute for Radio Astronomy Onsala Space Observatory
Altitude	5,064 m (16,614 ft)
Wavelength	0.2, 1.5 mm (1.50, 0.20 THz)
First light	2004
Telescope style	Cassegrain reflector cosmic microwave background experiment radio telescope
Diameter	12 m (39 ft 4 in)
Mounting	altazimuth mount
Website	www.apex-telescope.org
Location of Atacama Pathfinder Experiment
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The Atacama Pathfinder Experiment (APEX) is a radio telescope 5,064 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert in northern Chile, 50 km east of San Pedro de Atacama built and operated by 3 European research institutes. The main dish has a diameter of 12 m and consists of 264 aluminium panels with an average surface accuracy of 17 micrometres (rms). The telescope was officially inaugurated on September 25, 2005.

The APEX telescope is a modified ALMA (Atacama Large Millimeter Array) prototype antenna and is at the site of the ALMA observatory. APEX is designed to work at sub-millimetre wavelengths, in the 0.2 to 1.5 mm range — between infrared light and radio waves — and to find targets that ALMA will be able to study in greater detail. Submillimetre astronomy provides a window into the cold, dusty and distant Universe, but the faint signals from space are heavily absorbed by water vapour in the Earth's atmosphere. Chajnantor was chosen as the location for such a telescope because the region is one of the driest on the planet and is more than 750 m higher than the observatories on Mauna Kea and 2400 m higher than the Very Large Telescope (VLT) on Cerro Paranal.^[1]

APEX is a collaboration between the German Max Planck Institute for Radio Astronomy (MPIfR) at 50%, the Swedish Onsala Space Observatory (OSO) at 23%, and the European Organisation for Astronomical Research in the Southern Hemisphere (ESO) at 27%.^[2] The telescope was designed and constructed by the German firm VERTEX Antennentechnik GmbH, under contract by MPIfR.^[3] The operation of APEX on Chajnantor is entrusted to ESO.