Construction of ALMA

Workers at the ALMA Array Operations Site (AOS), located on the Chajnantor plateau at an elevation of 5000 metres in the Chilean Andes. At this altitude, the atmospheric pressure is about half of that at sea level. This, together with the extreme temperatures and dryness affects the machines, the behaviour of materials and, of course, humans working there. ALMA cooperates with Chilean and international medical institutes in the study of the long term effects of the high altitude on health. The reason for building ALMA at such a high altitude in spite of the additional difficulties it brings is that the millimetre and submillimetre radiation ALMA observes is strongly absorbed by the water vapour in the Earth´s atmosphere.