Atacama Large Millimeter Array
Interesting facts
- Costing about 1.4 billion US dollars, ALMA is described as the most expensive ground-based telescope in operation.
- The name ALMA was chosen in 1999; in Spanish the word alma means soul.
- For political reasons the antennas came from three different manufacturers, in the United States, Europe and Japan, each with its own design.
- Each large antenna weighs about 115 tonnes, and the German-built transporters that carry them have driver seats designed to take an oxygen tank.
- At its sharpest ALMA can resolve detail of about 10 milliarcseconds, roughly five times finer than the Hubble Space Telescope.
- ALMA grew from three separate plans: an American Millimeter Array, a European Large Southern Array and a Japanese Large Millimeter Array.
- The first image released, in October 2011, showed cold gas in the colliding Antennae Galaxies, invisible to optical telescopes.
- The Atacama Compact Array was named the Morita Array in 2013 after its designer, Koh-ichiro Morita, who died in Santiago in 2012.
- In August 2013 staff went on a 17-day strike, one of the first strikes ever to halt an astronomical observatory.
- The array observes at wavelengths between about 0.32 and 3.6 millimetres, between the infrared and ordinary radio waves.
Why it is worth it
High on the Chajnantor plateau in the Chilean Atacama, some 5,000 metres above sea level, sixty-six white dishes stand in a landscape of ochre dust and bare volcanoes. This is the Atacama Large Millimeter Array, ALMA, a single instrument built from many: fifty antennas twelve metres across, plus a tighter cluster of sixteen smaller ones known as the Atacama Compact Array. The site was chosen for what it lacks. At this altitude and in one of the driest places on Earth there is almost no water vapour overhead, and that is what lets faint millimetre and submillimetre radiation from cold gas and dust in space reach the ground.
What makes ALMA visually unusual among observatories is that it does not stand still. The dishes can be picked up by two enormous custom haulers, 28-wheeled machines of about 130 tonnes each, and set down on different pads, so the array can be squeezed into a knot 150 metres across or spread over a span of 16 kilometres. Seen together, the antennas look less like a building than a herd grazing on the plateau, and each reconfiguration changes the shape of that herd and the sharpness of the telescope's vision.
ALMA is run by an international partnership led by the European Southern Observatory, the US National Radio Astronomy Observatory and the National Astronomical Observatory of Japan, together with Canada, South Korea, Taiwan and Chile. Science observations began in 2011 and the full array has worked since March 2013. Its best-known image is that of the young star HL Tauri, where a disc of dust around the star showed concentric bright rings split by dark gaps, read as the tracks of planets being born. ALMA also took part in the Event Horizon Telescope campaign that produced the first direct image of a black hole, published in 2019.
The high plateau itself is a working site with no casual access. The public side of ALMA is the Operations Support Facility at about 2,900 metres, where the control room, laboratories and antennas brought down for maintenance can be seen, sometimes alongside one of the transporters.
Getting there
The nearest city is Calama, about 135 km away, served by El Loa Airport (CJC), roughly 130 km from the array. Visits start from the oasis town of San Pedro de Atacama, which lies about 35 km from the Operations Support Facility; the observatory's visitor bus collects registered guests there.
Plan your visit
We have no confirmed visit data yet. Once it is confirmed, this block also carries the date it was checked.
Nearby places
- Licancabur 24.5 km · volcano
On these lists
From the encyclopaedia
The Atacama Large Millimeter/submillimeter Array (ALMA) is an astronomical interferometer of 66 radio telescopes in the Atacama Desert of northern Chile, which observe electromagnetic radiation at millimeter and submillimeter wavelengths. The array has been constructed on the 5,000 m (16,000 ft) elevation Chajnantor plateau – near the Llano de Chajnantor Observatory and the Atacama Pathfinder Experiment. This location was chosen for its high elevation and low humidity, factors which are crucial to reduce noise and decrease signal attenuation due to Earth's atmosphere. ALMA provides insight on star birth during the early Stelliferous era and detailed imaging of local star and planet formation.
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