The ALMA (Atacama Large Millimeter/submillimeter Array) observatory lies high in the Atacama desert, close to San Pedro de Atacama. Costing $1.4 billion, ALMA is the world’s most expensive ground based telescope. The ALMA observatory itself is split into two facilities: at 3200 metres, the Operations Support Facility (OSF) which contains the administrative offices, maintenance facilities, and living quarters for the scientists who work on ALMA.
Even higher on the Chajnantor plateau at 5000 metres lies the array itself, consisting of 66 radio telescopes which can be moved up to 16 kilometres apart. The data from these telescopes is processed and delivered to astronomers at the OSF. By combining the observations from these 66 telescopes, ALMA scientists are able to make observations which would otherwise only be possible with a single much larger telescope (which would be impractical to build).
Since its inception ALMA has been offering free tours of the facility, which can be booked from their web page. As of July 2015 the tours operation only on Saturdays and Sundays. A bus collects visitors from San Pedro de Atacama at around 9am and returns around 1:30pm. This is the only way to visit the facility: private cars and individuals will be turned away at the gate.
The first thing to point out about visiting ALMA is that for safety reasons it is not possible to visit the telescope array, only the Operations Support Facility (OSF). There would be too many health risks associated with climbing so quickly to 5000 metres. Nevertheless, this is an excellent opportunity to visit one of the world’s leading telescopes, and I would strongly recommend anybody with an interest in astronomy to book a tour.
Our tour started with a rather long explanation of the ALMA project, from initial ideas in the 1980s through design and construction, to its current operations. To be honest this part of the tour became a little boring – it was overly long (over an hour) and we were standing in a corridor for most of that time. However, there were some interesting explanation panels along the corridor which you could read at your own speed. These panels explained the use of telescopes arrays to observe the sky (rather than a single huge telescope) and how the data is collected and processed. There were also some stunning images from the observatory. One of the things which made this first part of the tour somewhat frustrating was that it was followed by a short video – which explained everything the guide had just told us, but in about 10 minutes! To be fair to the guide our group was quite large (over 40 people) and he was very enthusiastic and willing to answer any and all questions.
More interesting was the second half of the tour, as we moved through the ALMA buildings. We were able to visit the technical operations centre where repair and maintenance work is carried out (we could only observe through glass as the whole area is a clean room and protected from static discharge). Here another ALMA engineer explained his role in the facility.
There was also the opportunity to visit the ALMA control centre – a remarkably ordinary looking space consisting of a small number of desks and computers. From these scientists are able to monitor and control the entire ALMA array. Because of the wavelengths of light being observed, the radio-telescopes do not suffer from interference from daylight and as such can work 24 hours a day. The astronomer here did a good job of explaining the function of the computers at ALMA, including the collection of data (93 GB/sec from each telescope!), and its reduction by the computing systems to produce approximately 1 terabyte of data per day.
For me the most interesting part of the tour was really down to sheer luck. By coincidence two of the radio telescopes had been removed from the array and were at the OSF for maintenance. After donning hard hats we were able to walk right up to the telescopes themselves and even venture beneath the giant yellow ‘Otto’ vehicle which is used to transport them. Seeing the telescopes so close really seemed like the highlight for most people on the tour so if you are lucky, one might be broken when you visit too!
ALMA tours are free and can be booked from the observatory’s website. Our guide was fully bilingual but as most of the tour participants understood Spanish, the tour was almost exclusive in Spanish. This was not a problem for me, but there were two people who spoke only English who must have felt a little left out. It might be worth checking if this is likely to be an issue for you. All of the visual materials and explanations in the visitors’ centre were in both English and Spanish.