Timelapse of Orion rising over the ALMA array. The constellation Orion is seen rising from behind the telescope at right. At far right is Sirius, the brightest star in the night sky. 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.