Atacama Pathfinder EXperiment telescope, APEX, is at the highest observatory site on Earth, at an elevation of 5100 metres, high on the Chajnantor plateau in Chile's Atacama region. APEX is a 12-metre diameter telescope, operating at millimetre and submillimetre wavelengths — between infrared light and radio waves. Submillimetre astronomy opens 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 is an ideal location for such a telescope, as 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.

Photo: The APEX Telescope. 

APEX is a leg of Around the World in 80 Telescopes tour: Click to play; click  (lower right) to view video full screen Next stop: ALMA (previous stop: Teide)

The APEX Telescope is the largest submillimetre-wavelength telescope operating in the southern hemisphere. It has a suite of different instruments for astronomers to use in their observations, a major one being LABOCA, the Large APEX Bolometer Camera. LABOCA uses an array of extremely sensitive thermometers — known as bolometers — to detect submillimetre light. With almost 300 pixels, it is the largest such camera in the world. In order to be able to detect the tiny temperature changes caused by the faint submillimetre radiation, each of these thermometers is cooled to less than 0.3 degrees above absolute zero — a frigid minus 272.85 degrees Celsius. LABOCA's high sensitivity, together with its wide field of view (one third of the diameter of the full Moon), make it an invaluable tool for imaging the submillimetre Universe.

APEX is a pathfinder for ALMA, the Atacama Large Millimeter/submillimeter Array, a revolutionary new telescope that ESO, together with its international partners, is now building on the Chajnantor plateau. APEX is based on a prototype antenna constructed for the ALMA project, and it will find many targets that ALMA will be able to study in great detail. ^[1] 

APEX, the Atacama Pathfinder Experiment, is a collaboration between Max Planck Institut für Radioastronomie (MPIfR) at 50%, Onsala Space Observatory (OSO) at 23%, and the European Southern Observatory (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 APEX telescope is operated by ESO.

Observing with APEX will allow us to study warm and cold dust in starforming regions both in our own Milky Way and in distant galaxies in the young universe. High frequency spectral lines enable the exploration of the structure and chemistry of planetary atmospheres, dying stars, molecular clouds as well as inner regions of starburst galaxies. We will address issues from the vast scales of the structure of the Universe down to the physics and chemistry of comets. [2]  READ MORE »