English: When completed, the antennas of the Atacama Large Millimeter/submillimeter Array (ALMA) will be spread across the Chajnantor plateau in the Chilean Andes over distances of up to 16 kilometres, but they will work in unison, to form what is known as an interferometer. In doing so, ALMA will be more powerful than the sum of its parts, acting like a single giant telescope as large as the whole collection of antennas.

The 66 ALMA antennas are not all the same. A main array of fifty antennas with 12-metre dishes will be complemented by the Atacama Compact Array (ACA) of twelve smaller 7-metre dishes and four additional 12-metre dishes. The ACA dishes are being constructed by Mitsubishi Electric Corporation (MELCO). Three of them are shown in this photograph of the MELCO Site Erection Facility at the ALMA Operations Support Facility (OSF) site. The OSF is at an altitude of 2900 metres, from which the completed dishes are transported along a 28 km road to the 5000-metre altitude of the Chajnantor plateau.

On the left is one of the 7-metre dishes, clearly smaller than its neighbours. The other two dishes both have a diameter of 12 metres, but subtle differences in their design can be seen. This is because the dish on the right was originally a prototype, used for testing during the early stages of the project, which has since been retrofitted with elements from the final design of the dish in the centre. Once ready, all these dishes will take their places on the high Chajnantor plateau.

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.

This photograph was taken by ESO Photo Ambassador José Francisco Salgado.

Links

• ESO Photo Ambassadors webpage