ALMA antennas reach double digits at Chajnantor

The number of antennas for the Atacama Large Millimeter/submillimeter Array (ALMA) on the Chajnantor plateau has now reached double digits! The tenth antenna was moved up from the Operations Support Facility at an altitude of 2900 metres to the Array Operations Site at 5000 metres, high in the Chilean Andes, on 4 March 2011 using one of the ALMA transporter vehicles.

ALMA is a telescope designed to observe millimetre- and submillimetre-wavelength light with its array of antenna dishes. Using a technique called interferometry, ALMA acts like a single giant telescope as large as the whole set of antennas. Thanks to the transporter vehicles, the antennas can be arranged in different configurations, where the maximum separation between them varies from 150 metres to 16 kilometres.

The distant viewpoint of this photograph is necessary for one to see all ten of the antennas in a single shot. Nine of them, including the newest addition, are clustered together on the left of the image, but the tenth is about 600 metres away on the right. ALMA is currently in a testing phase, and this lone antenna allows the astronomers and engineers to test the system’s performance with a longer baseline — the separation between a pair of antennas. When ALMA construction is completed in 2013, there will be a total of 66 antennas in the array.

The rare cloudy sky seen in the photograph is due to the Altiplanic Winter, in which the jet stream reverses and brings moist air from the east to this usually extremely arid site.

The ALMA project is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ESO is the European partner in ALMA.