Astronomy Picture of the Day

Explanation: It is the most expensive and complex ground-based astronomy project ever -- what will it see tonight? The Atacama Large Millimetre Array (ALMA) project consists of 66 dishes, many the size of a small house, situated in the high altitude Atacama Desert in Northern Chile. Together, ALMA observes the skies in high-frequency radio light, a band usually used only for local communication due to considerable absorption by humid air. The thin atmosphere and low humidity above ALMA, however, enable it to see deep into our universe in new and unique ways that allow, for example, explorations of the early universe for chemicals involved in star formation, and observing local star systems for signs of disks that form planets. The above time-lapse video shows the course of four ALMA antennas over one night. The Moon sets early in the video, while three dishes repoint in unison. Background stars continually rotate up, the central band of our Milky Way Galaxy pivots around and eventually exits off to the right, while halfway through the Small and Large Magellanic Clouds -- satellite galaxies near our Milky Way -- rise up from below the horizon. Car headlights momentarily illuminate the dishes, while an occasional Earth-orbiting satellite crosses overhead. Daylight ends the video but not ALMA observations -- which typically run both all night and all day.