ALMA from above

Shown here is the Atacama Large Millimeter/submillimeter Array (ALMA), located high on the Chajnantor Plateau in the Chilean Andes, 5000 metres above sea level.

The rocky edge visible in the foreground of the image is a mountain that looms above ALMA. It is here that the 1-metre pathfinder telescope, called MiniTAO, is situated. MiniTAO is part of the University of Tokyo Atacama Observatory (TAO) project which will later see the construction of a larger 6.5-metre infrared optimised telescope on the site.

NAOJ, ESO and the other partners involved in ALMA selected this site because it is one of the highest and driest astronomical observatory sites on Earth.

ALMA is comprised of 66 high-precision antennas spread over a distance of up to 16 kilometres. The antennas use a technique known as interferometry to combine their signals, enabling them to act as a single giant antenna.

Signals from each of the antennas need to be combined with perfect synchronicity — a precision of one millionth of a millionth of a second. They are collected at the ALMA correlator (just out of view in the image), ALMA’s central computer, where the accuracy of the path followed from each antenna must be known to within the diameter of a human hair.

In 2013, ALMA was inaugurated at an official ceremony, which marked the completion of all the major systems of the array and the formal transition from a construction project to a fully-fledged observatory. The array explores the enigmatic cold Universe at millimetre and submillimetre wavelengths, a largely unmapped part of the electromagnetic spectrum.