Timelapse of the night sky over the ALMA array. ALMA (Atacama Large Millimeter/sub-millimeter Array) is an array of 66 radio telescopes located at an altitude of 5000 metres on the Chajnantor plateau, in Chile's Atacama desert. Data from the separate telescopes is combined by interferometry, making it one of the most powerful and complex observatories in the world. Observations began in 2011, and the array is scheduled to be fully operational by the end of 2012.