Getting to the Atacama Large Millimeter/Sub-millimeter Array (ALMA) radio observatory is done via road. The nearest town with lodging is San Pedro de Atacama, a town of about 3900 people at an altitude of 2400m (7900 feet). Getting to San Pedro is also by car, about an hour and a half southeast from the city of Calama. Calama has an airport and takes the major jet flights from other cities in Chile.
The landscape is at first barren in appearance, and one would be correct in keeping to this belief: No surprises… it is a desert! Most of the area is dry desert, dry, high-altitude desert. There are occasional stands of trees (government experiments) that run here and there in the regions between towns, but otherwise it is a hard packed sand, gravel mix with lava flows from the volcanic activity which is still very much alive. Arrival in San Pedro takes one off of the highway route 23 and into a world of high adobe packed walls, dirt roads and dust. The landscape is sparse, again from the viewpoint of driving around town. Behind those walls? There are some pretty nice homes in there, trees and gardens, hotels, restaurants, shops: it is a bustling little town full of things to discover and enjoy!
People make their way about town on foot, bicycle, and car. One has to be very careful while driving, as there are no street signs, stop signs, warning indicators, etc, and the walls are too high to see around. It is not uncommon to have a swift-moving bicycle cross your path as you drive the streets.
Each doorway can lead to any possible outcome! There are restaurants, clothing stores, textile shops, astronomy tourism centers… all located in there!
Located just off to the side of the main square (Plaza de Armas) is the San Pedro church, an active Roman Catholic church, and one of the oldest constructed in Chile. The church is now an historical site along with San Pedro’s oldest structure, Casa Incaica, which dates back to 1540.
There are a lot of dogs making their living in San Pedro – they wander the streets and call the whole town their own. People lovingly care for all of them, knitting them sweaters, feeding them throughout the day, and giving a pat on the head. The little fella in the photo below followed us as we made our way to a local bakery – some of the finest croissants in Chile, I must say! He knew where to get a meal!
One does not simply go to Chile and not try the local foods. I happen to love tamales, and they had them, and with llama! Delicious.
San Pedro is the nearest large town to ALMA. It is a good drive out through the desert to the site. ALMA itself has two main locations, or bases of operation: the “Low Site” and the “High Site”. Altitude makes a lot of difference to human activity! The low site is the Operations Support Facility, the OSF, at an altitude of 2900m. The high site is the Array Operations Site (AOS) and is much higher: 5058m which just takes one’s breath away!
Entrance to ALMA requires a few checks: One has to stop at the entrance gate for some basic safety training, a short safety video and identification with the guards. The view from the main road, Route 23, is pretty spectacular. Volcanoes stretch across the horizon, and they are still geologically active.
Once at the low site, there is the constant safety reminder in plain site: UV radiation here and at the high site is usually at the “Extreme” level resulting in terrible sun burns should one not take precautions. I used SPF110 and was ready with hats. In the winter, as when we were there, it is a bit easier to be cautious with UV, as it gets cold up there! Not much skin is exposed.
The operations center has the needed controls for operating the whole array. There are basic status boards and controls for every necessary activity on site. Safety demands that people only work at the high site for 4 hours before needing to return to lower altitudes to give their bodies a rest. We were quite happy to have been at Cerro Tololo only days before: that helped a lot with acclimatization.
Outside at the high site, the antennae were arranged closely together. They are moveable with array sizes ranging from 150m to 14km.
Maintenance at the high site is an ever-ongoing process. Technicians are able to be at the site for 4 hours before needing to return to lower altitudes. The antennae need great attention, as they are very sensitive devices. Each is cooled by Helium, powered and placed in precise locations for operations. Keeping all this going in a land that is dusty, windy and experiencing temperature extremes is a big challenge!
Antennae below are a little further away from the array’s central cluster on this day. In the background one of the many volcanoes that make the whole area.
There are two different antenna sizes at ALMA: 12m and 7m. They receive photons through the <remaining> atmospheric windows between 350 μm and 10 mm. Resolution depends on the array’s configuration, as the whole system operates as an interferometer. They have gotten to 10 milliarseconds, which is a huge accomplishment, as this is 5 times better than the Hubble Space Telescope’s ability, and ten times better than the Very Large Array’s ability.
Safety is a huge issue for ALMA and those that work there. We carried portable cans of Oxygen for a sip here and there. Let me be the first to tell you just how good it felt to get re-oxygenated once levels in the blood got to the mid-70% range. Low levels bring a person to hypoxia, something I am no stranger to as a pilot…. but one of the great equalizers of hypoxia is a general sense that all things are good, great in fact… illusory euphoria. Nice! Having 90% blood Oxygen is good, and it was easy with a quick shot or two from the cans.
Getting to a higher point on the plateau, one could see the entire array the day we were there. There was a light amount of snow also present, which was rapidly sublimating away into the very dry desert air.
There is a huge level of technical know-how going on behind the scenes at ALMA. All the antennae have FDDI feeds (fiber optics) to the central processing unit, “The Correlator”. When using many antennae, photons from their object of study arrive at very slightly differing times at each antenna. This is simply a matter of geometry. Photons from one source arrive at the closest antenna first, and hit the most distant antenna last. All this received data has to be aligned temporally before it can be analyzed scientifically. This is the job of the supercomputer called a correlator. The one at ALMA resides at the high site and has the equivalent of 134 million processors… some 20 million solder joints! That is a lot of power.
As noted earlier, each of the antennae are moveable, and with some incredible precision. Getting this done is no easy task. A specially designed and built transporter “truck” was designed and constructed just for this task. As an antenna is built and tested, it then must go up the path from the low site to the high site. This beast of a machine gets that done with the aid of very skillful drivers. The transporter has 14 independently steerable (and fully adjustable in height!) wheels, each of which is also independently powered. Ok! A 14-wheel drive vehicle! This machine lifts an antenna into a well-held mount and powers both itself and the antenna using two large diesel generators. The antenna must remain powered at all times: remember that it is cooled with compressed, super cold liquid Helium! There are two transporters, named Otto and Lore, and the best part? They can be controlled using a hand held remote control unit.
One nifty little techy trick is that the iPhone (and many others) have built in GPS and compasses which imbed geo0location metadata into your photos. Here’s the array seen from inside the high site operations center. Yes, that is 16,500 feet.
It was very windy and cold out there that day: little worry for a sun burn given that we were so bundled up in June, a.k.a. winter in the southern hemisphere. Frigid had a good time!
If you happen to be visiting the ALMA sites, you are also near one of the most interesting places in the Atacama, the Los Flamencos National Reserve. Yes, there is water out there, but it is VERY salty! Two large salt flats reside at the high altitude plateau in the Atacama: the Tara and the Aguas Calientes. The salt is pushed up out of the earth by hot springs. As the water evaporates it leaves behind fascinating crystal formations right on the surface of the desert… stretching for miles.
It would not be Los Flamencos without a…. flamingos! This particular species is the James flamingo and they just love to eat the brine shrimp that reside in the salty waters. Shrimp? Yep!
The ALMA trip is a wrap!
More about The Astronomy in Chile Educator Ambassadors Program (ACEAP), please visit their pages at the National Radio Astronomy Observatory website here: ACEAP.