Several dishes in the ALMA array, which is located at 16,700 feet above sea level on the Chajnantor Plateau. // All images: Astronomy: Alison Klesman
Saturday morning, the ACEAP ambassadors dutifully forewent their coffee in preparation for the physical required to visit the “high site” at the Atacama Large Millimeter/submillimeter Array (ALMA) Observatory. The Array Operations Site, or AOS, is located about 16,700 feet (5,000 meters) above sea level – which is why there’s a short physical required prior to ascending. This site is where the 66 radio dishes and the correlator that processes the signals they receive are located; when ALMA is operating, it’s these systems doing all the work. The final signal is then sent to the Operations Support Facility (OSF) via fiber-optic cables, where it can be monitored during data collection and then stored for retrieval by the astronomers who have successfully proposed for time on the array.
Visiting the high site is uncommon, but as ACEAP ambassadors, we were allowed the opportunity – provided we passed that physical.
One by one, we were called into the back of the medical clinic at the OSF, which is “only” at about 10,000 feet, to have our blood pressure and heart rate checked. The body responds to high altitude by ramping up both, typically, so if yours is too high at the lower of the two ALMA sites, you aren’t allowed to visit the high site. And one by one, we trickled out the door with the same answer: We passed!
Ultimately, the entire group of 2017 ACEAP ambassadors was cleared to visit the ALMA high site. Prior to departure, we piled on several layers of clothes after we were informed that the temperature was about 20 degrees Fahrenheit (-6 Celsius); fortunately, there was very little wind, which we were told can be brutal. We were outfitted with several tanks and small canisters of oxygen, then piled into two vehicles and began the drive up to the Chajnantor plateau, which houses the ALMA array.
One of the many vicuñas we spotted on our way up to the ALMA array.
The drive was nothing short of stunning, with spectacular views of the Atacama Desert below as we climbed ever higher. We even saw a few burros and vicuñas, which are (as far as I can tell) the slightly smaller, definitely cuter cousin of the llama. Our driver, Valeria Foncea (who works in education and public outreach for ALMA), was kind enough to slow or stop every time we spotted something we wanted to photograph, though we tried not to overdo it, given how much all of us wanted to reach our final destination.
About 30-40 minutes later, we came to the end of the road: the ALMA array! Our first stop was the operations building that houses the correlator, which was described to us as “the brain of ALMA.” This equipment is responsible for combining the signals received from each dish in the active array, turning it into a final data product that astronomers can use. The correlator itself is in two parts: One half was built in North America, and the second in Japan.
The North American-built half of ALMA's correlator.
That same building also contains the high site’s medical clinic, which I admit I saw about 15 minutes into our tour of the facility, as I was feeling pretty lightheaded (though still on my feet, which I consider a win). Fortunately, it was nothing a little extra oxygen couldn’t fix, though I was told to stay in the car once we drove out to the antennas, rather than walk around with the rest of the group. Honestly, it worked out fine, as you can see – I set myself up on the backseat with the door open, the windows down, and got to ogle the antennas plenty from a comfortable seat! Given the altitude, most of the ambassadors didn’t go far, either.
After much too short a time at the high site, it was time to head back down. Visitors like our group aren’t allowed to stay at that altitude for very long, positive physical or not. The drive down afforded views that were just as beautiful, even if they lacked the anticipation of traveling to a place where there’s only a small fraction of the oxygen available at sea level to stand among some of the most advanced radio astronomy equipment on the planet.
I know I’ve said it before, but I want to say it again – I feel truly honored to be a part of this group, especially given the unique opportunities we’ve had, which are typically not afforded to other visitors to these observatories. It’s not often that groups are allowed to travel to the ALMA high site – certainly astronomers don’t visit it, and for the most part, the only people who make the trip up to 16,700 feet are technicians and those responsible for the operation of the correlator computer system. The fact that I had the chance to see what I consider both a major technical feat and a huge, huge asset to our current (and future) astronomical community is something that I will treasure for the rest of my life.
Following lunch, we had a short presentation by Sergio Cabezón, the Education and Public Outreach officer for Associated Universities, Inc. and the National Radio Astronomy Observatory in Chile. Sergio also accompanied us for the majority of our trip through Chile, providing translation, guidance, and many, many entertaining jokes and stories. His local knowledge and his passion for astronomy education and outreach were both obvious throughout the week, culminating in a talk highlighting his past, current, and future work to continue promoting astronomy and other STEM education and interests in Chile on behalf of AUI, NRAO, and the observatories we were privileged to visit.
The salt marsh at Reserva Nacional de Flamencos.
We rounded out the day with a visit to Reserva Nacional de Flamencos, which is a huge salt marsh that serves as a home to – you guessed it – numerous flamingos. The landscape of the Atacama Desert is unlike anything I’ve ever seen, and the Reserva did not disappoint. After returning to our hotel briefly to regroup and grab equipment, we took a short jaunt outside San Pedro after sunset to view the southern sky one last time. I managed to get a few more photos of the night sky, again with the help of our astrophotographers, to whom I am eternally grateful for their patience and assistance. Although fainter than at CTIO, we were able to see the zodiacal light, which is something I have read about countless times but had also never seen for myself before this trip and the crisp, dark skies it afforded.
The zodiacal light, as seen from outside San Pedro.
Finally, it was time for a (late!) dinner, then packing in preparation for leaving San Pedro in the morning…