search this site
HomeProject Manager's Corner

Thirty Meter Telescope

My Summer Vacation in February
Gary Sanders, TMT Project Manager

Yes, in February. I know that readers of this page are now enjoying the beginning of summer and school is now out and so the summer vacation trek begins. But that is a Northern Hemisphere view. My summer vacation was in February. In Chile. There it was summer.

It was really a business trip with serious work involved, both physical and mental. But the locations visited and the departure from our normal lives and the expedition quality and nearly complete breaking of contact with the project office back home made it feel like a vacation. And my wife was along. She served as expedition photographer on a marathon TMT trip to visit nearly all of the northern Chile sites being studied as candidate TMT observatory locations.


It stands to reason that the world’s best telescope will need the world’s best site, or at least the best site that we can gain access to. And it must be a practical site, so Dome C in Antarctica seems out. But sites in Hawaii, Mexico and northern Chile were identified in early screenings and TMT has set out an ambitious program to carefully measure the quality of "seeing" on these mountains.

The site must have superb astronomical "seeing," a quality that is not just lack of dust and clouds and light pollution, though those are important. What is really important is that images of a skyward "dot" must be a dot. Not a blur. Not twinkling on and off. A dot as close to the real size of the image of the dot as possible. For this to happen, light from that star or galaxy or cosmic feature and its nearby region must travel through the atmosphere and all arrive at the telescope together. After passing through many kilometers of Earth’s atmosphere, all that light must arrive no farther ahead or behind the adjacent light by more than about the size scale of atoms. The culprit is layers of the atmosphere that are more or less dense. How can that happen? Layers of the atmosphere with temperature differences (remember warmer air is less dense) will ruin good astronomy.

So an even temperature atmosphere, even with some wind, is what we look for. Air moving around is okay if the temperature is the same. When you see heat waves rising off the surface of a road ahead of you, you are seeing bad "seeing". You do not want to look up through such an atmosphere and attempt frontier astronomy.

Of course we care about high winds rattling our telescope. We care about cloudy nights and water vapor absorbing some spectral lines and whether patches of sky that are good are small or large, or how long the good times are each night. So it is complicated.

To find the best mountains, several years of data are required to even have the flimsiest reason to guess how a mountain might serve for 30 years. We know that weather and the atmosphere have periodic cycles. There is always a bit of a gamble.

Astronomy sites tend to be on mountain tops. High and clear. Better dry. Good weather. That lets out any good ski areas.

In fact, they tend to be on coastal or island mountains where ocean breezes help maintain clear dry conditions and the air flow is smooth and undisturbed. Observatory sites like Hawaii and the Canary Islands and coastal ranges in Chile are renowned for good conditions.

Or they tend to be further inland and higher and drier. Mountains in the Atacama desert region of Chile fall into that category. The Atacama desert is the driest in the world (again except for Antarctica). Some locations there claim to have had no precipitation in hundreds of years. No bugs. No plants. No birds. Nothing. Like being on Mars. And that is what we found. Visiting the Atacama was like an exotic vacation. Read on.

Robot Eyes

To test the seeing, we have placed telescopes and instruments on candidate mountains. The intrepid TMT site testing team (Footnote 1) has this robotic testing equipment running on mountains in Chile and Mexico and, as I am typing this story, are beginning operations in Hawaii. Data is streaming in.

On each mountain, every night at sundown, on top of a 6 meter tower, a fabric covered half-egg shaped dome opens under computer control. (Figure 1) Revealing a small telescope that could fit into a pickup truck (Figure 2), the robotic scope begins a night-long campaign of pointing towards preselected stars and calibrates itself and collects image data. The data is stored on disk drives on the mountaintop in racks below the tower. The data is also sent by fiber link or microwave link (depending on the mountain) across the internet to one or more TMT partner sites. Sonic ranging devices measure temperature layers in the atmosphere by echos. Other devices measure water vapor and cloud cover. Solar panels power the systems. Web cameras are mounted on the towers connected to the internet. At dawn, the fabric dome trundles closed and the telescope parks itself under the protective shroud.

You can sit in Pasadena (or anywhere on the internet) and log into these remote mountains. You can read the data, checking, for example, how good it was last night. You can access the web cameras and see how things look. Mountain vistas. Your colleagues visiting and checking things. With your latte next to you in Pasadena, you can peek in on the activities.

You can wait for two years, plot out the data and you know the answer. This mountain is bad, that one good, that one better and the best is over there. The choice is clear.

Not so fast. Choices like this cannot be made by readouts from robot telescopes. Some mountains are easy to get to. Some require building the very first access roads. That costs money. Dust from nearby mining. Infrastructure from the local community. And so on. There are practical issues that will influence the choice.

We have to build summit facilities. Power. Winds from nearby mountains. Prevailing wind directions. What these all mean is that you have to go to the sites and explore and ponder each one. Our intrepid testing gang has been to all sites, of course. But what about the white-haired decision makers?

I had learned from prior projects that maps and books and reports and data are not enough. You have to go and get the feel of the place.

Setting Out

So, on February 3, eight of us flew to a marathon inspection of each site in northern Chile. We began in Antofagasta, Chile. Fly down to Santiago no matter where you come from in the world and then on to Antofagasta, a coastal town 900 miles north of Santiago.

Led by our Site Selection Group Leader, Paul Gillett, and the Site Testing Leader, Matthias Schoeck, both from the TMT Project Office, but really organized by our senior scientist in Chile, Bob Blum of the AURA-managed Cerro Tololo Inter-American Observatory, we converged in Antofagasta. The expedition was filled out by Jerry Nelson, the TMT Project Scientist (UC Santa Cruz), George Djorgovski, co-chair of the TMT Site Advisory Group (Caltech), Eric Steinbring, site testing leader from our Canada partner (Herzberg Institute of Astrophysics), and me, TMT Project Manager (with white hair). And my wife Marjorie, sole female, chronicling our journey through the lens of her Canon SLR, consultant on the livability of each site (not much to say), consultant on the relative safety of steep mountain switchbacks (much to say) and doomed to endure harsh conditions and little privacy in this highly motivated male siege.

We met at our hotel in a parking lot with four Hertz rental Toyota Hilux 4 wheel drive trucks. Just two to a truck because backseat passengers cannot see the bumps well enough to brace themselves safely. Head banging is part of astronomy. Ouch!

Toyota Hilux. Not available in the USA, this small truck is pervasive around the world. A simple (no electric seat adjusters) truck. A go-anywhere manual shift with 4-wheel drive low-range truck, roll bars with a light on top and no less than two spare tires (It is a long walk back from some of these places). Back seat filled with luggage (no dust inside) and jugs of water and truck bed loaded with tires. With air conditioning. The perfect truck for traveling across Afghanistan. Or Iraq. Or the Atacama desert.

Cerro Z

Leaving the Hotel Antofagasta we set out for the first TMT site, a coastal 3000 meter mountain called Cerro Z. Several hours on long straight flat and very dusty roads and you approach the Cerro Z cone. Our first really steep passage up a slope by way of switchbacks and some thrilling dropoffs lands us on the summit amid our equipment. These Hiluxes do the job.

(Figure 3) There we see our 6 meter tower, the special Halfmann telescope, the solar panels, our array of electronics cabinets, a weather station and cables and all of the things to turn this remote outpost into a forward sentinel for our grand telescope of the future. We familiarize ourselves with the equipment, check everything to be in working order, and a few climb the tower to get the full tour. (Figure 4)

But what we are really here for is to look at the region, the surrounding terrain and neighbor peaks and to imagine what it would be like to build and operate an observatory in this remote outpost. Nearby mountains and prevailing winds do not seem to threaten this peak with turbulent flow. The distance traveled from Antofagasta is not too far (!). The slope makes it easy to imagine summit facilities high up and lower elevation support facilities down below. Though it is calm today, this peak has frequent windy conditions. A promising site but let’s wait for all of the data. (Figure 5)

Across the valley to the west we see the neighboring coastal peak of Paranal, home to the 4 telescopes (8 meter mirrors) of VLT, run by the European Southern Observatory. They have made it work out here. But they have also experienced an apparent shift in the prevailing wind direction since they did their testing. This fluctuation in weather has caused deterioration of their seeing, though they are still at the front of the pack of large telescopes in publishing cutting edge science. The pendulum and winds will swing back but the experience is sobering for the next generation.

Our expedition creeps down the switchbacks, four trucks in a queue. Past the site of the small observatory run by the Universidad Católica del Norte. Thrilling, sunny, warm, breezy and otherworldly.

Across the dry flat valley, guided by GPS and poor maps. We realize that we have taken a wrong turn and do not know which of the unmarked dusty tracks is right. We are lost? No, says one of our genius colleagues. With our GPS, "we know our location exactly…". But we do not know which path ahead is right. And the map says "Valle de la Muerte". Great.

A little driving in circles and we are back on track, thumping along the straight and dusty roads. Now it is easy.

Ore trucks. Really big tractor trailer ore trucks are a regular fixture on these remote roads. We are visitors here today with our LL Bean’s clothes and Garmin GPS’s. But they are here everyday running many tons of stone from point A to point B as fast as they can go. Across these same dusty tracks. Fast. Huge rooster tail plumes of white dust make them visible for many miles as they approach. Anticipation is not equal, though, to the sudden arrival of these hurtling behemoths, yielding no track to us, headlights on, diesels roaring, get over to the side and stop stop stop and the giant thunders by and there is a whiteout like a blizzard and you wait, frozen, and then it is quiet and the dust settles and you peer across to the other Hiluxes and they are still there. And you now know why Bob Blum, in our lead Hilux, called out "truck" on the little two way radios as the ore monster approached. A warning repeated many times in our trek. Who said astronomy was safe?

Down the last coastal dirt tracks, mining's tailing piles about, to the vista of the Pacific and Antofagasta. A sea port and a mining hub, rustic and hard scrabble but a metropolis in northern Chile as we shall see. And we are rewarded by pisco sours. A highlight of any visit to this region, this drink is made by simple recipe; a bottle of Pisco, a cup of lemon juice, sugar to taste, and ice. High octane! It is perfectly matched to a dusty palate in a region with centuries between rain. Sweet and sour and just right.

Departed Souls

Sunrise and loads of water jugs and luggage and we travel up the coast highway (yes, it seems like the southern hemisphere version of the California Pacific Coast Highway but drier) to Tocopilla. Here and there we encounter coastal camping. It is February in Chile. Not exactly August on the French Riviera, but the same pattern of the big vacation month sends these families yearning for breezes and scenes and renewal.

Past roadside shrines marking recent fatal vehicle accidents, we travel up the coast. The shrines, dubbed "animita" for "departed soul," each tell a story. Carefully prepared, different in design, tended lovingly with flowers, range from simple settings with crosses to a grand display of a little church or chapel with a model tanker truck on top. Perhaps this one signals the loss of a father or son or husband who drove such a truck in happier moments. They are everywhere, chronicling the sudden passage of our kind out of this life. Together, hour after hour, day after day on this trip, they tell a story of rural Chile and the families who dwell here.

Tocopilla and Cerro L

If Antofagasta seemed to be a remote outpost, Tocopilla is the next level of far away and out there. Smaller, coastal, not a big port, and no hotel to match the one last night. The Hotel Atenas is as basic as you can imagine, but with a proprietor beaming through his Greek gaze, recognizing some of our group from past trips, and most attentive. We drop our things and most of us head out to a quick visit to L.

Again, through the terrain of another drier world we wind our way on a dirt track. 90 minutes later we see the cone ahead. (Figure 6) Our equipment speckles the summit and the road up the mountain is as direct and sudden in its climb as yesterday’s approach was serpentine. No Cerro Z switchbacks here to slice up the climb. Now 4-wheel drive low is needed for the direct crawl up. Up we go, a sense of creeping and vertigo about us and the feel of soft and slippery talcum. We arrive.

Much the same equipment layout. Familiar now and checked and prodded. This summit is surrounded by a chain link fence, separating an amateur radio club transmitter from the dreamers who look up. An Entel wireless telecom installation is our link to the world. Our remote hopes feed into and depend upon technology.

L seems well suited for TMT. Separated from neighboring peaks, a bit more remote than Cerro Z. As before, let’s carry on and collect our data.

Calama, Chuquicamata and San Pedro

The next morning marks our departure from coastal mountains. We travel inland through the major city of Calama, hub of the northern mining region. A major airport serves this town and it sits just below the Chuquicamata mine, the world’s largest open pit copper mine. It is truly vast with its own town appended to the operation though now the populus is relocating to Calama.

The earth opened up. Ant-like giant vehicles creep about in the distance. One monster truck perches on the edge of a steep slope above us, rear tilting and disgorging what must be a house-sized pile of rubble. Down the slope the dust cascades. The iron and rubber colossus teeters on the edge of the steepness. One false move…

Dusty again we provision in Calama at a southern hemisphere Walmart-like megastore. Air conditioned with a vengeance and rows and rows of cookies and soda pop and jugs of water and Pringles. Pringles. Got to maintain that salt balance.

On to San Pedro de Atacama. Ecotourist oasis and style icon of the Atacama region. This tiny hamlet out-Santa Fe’s the US Santa Fe, NM. Dirt streets, charming adobe walled compounds, upscale hand carved and shiny varnished signs on old shop facades, restaurants in open plazas with open fire pits under portals and waiters who look like the crew from Pirates of the Caribbean. And internet cafes. A conquistador rides by on a loping horse. Leather vest and drooping hat and the face of the Spanish conquest. Passed by a $3000 dollar composite mountain bike. Biker garish in skintight yellow lycra, he sports a polycarbonate crown that would have served the conquistadors well. Old and new and growing its cuteness, San Pedro is the mecca of the Atacama and a place we rest for the night and feast in smokiness under the deep dark sky. Pisco sours.

Morning comes and the expedition visits, by a paved road, the 16,500 foot Chajnantor plateau, site of the Atacama Large Millimeter Array (ALMA) project. This North American-European-Japanese array is the current frontier mega-project in millimeter radio astronomy. Requiring a very dry atmosphere, ALMA must be high. We are considering a few peaks in this rarefied atmosphere and we operate a weather station on one 17,000+ foot altitude peak. To contemplate building and staffing an optical observatory at a place where supplemental oxygen must be breathed by the staff is not our first choice. We will watch the progress of ALMA and study our data at lower altitude summits and keep this possibility on our list. But just barely. Three of our team (stalwarts Bob, Eric and Matthias) do carry out a side journey, later in our expedition, above 17,000 feet to our little weather station, maintaining this rarefied option.

An evening visit to the Valle de la Luna at sunset reveals an other-worldly scene. Can this be Earth?

A wonderful dinner next to a pit fire under stars, pisco a flowing and we retire for a more rugged next day.

Cerro CH

Now inland we are going to study a mountain higher than the 3000 meter (10,000 foot) class Cerro Z and L. To achieve good seeing without the scouring of sea breezes, we have learned that we must go high. We travel across a new kind of terrain, with some vegetation and weather to Cerro CH, in the 4000 meter class. We pass by llama herds and tiny farms and come to rough roads and climb to the foot of a cone.

TMT has not yet conquered Cerro CH. While our stalwarts have visited we have no great equipment on top. There is no road or dirt track. Just a flat plateau with a bit of scrub confronting a cone. (Figure 7) But this mountain is higher than Mauna Kea in Hawaii. It is high. It is promising.

Our purpose today is to scout the area, consider where to grade a road and to look at prevailing winds and what is nearby. Remember, neighbor peaks may disturb the airflow and cause turbulence and disturb the seeing. You can study these questions with topographic maps and satellite photos. We did that. And computer visualization and aerodynamic studies in the computer and in wind tunnels with scale models. We did that and continue that. We use sophisticated techniques like computational fluid dynamics. But we also use going there and looking. This is too important to leave to models.

We stop at the foot and gaze upwards and we pause for a tailgate feast of watermelon and Pringles and chocolate chip cookies and just plain water. Paul and Eric drive about the cone considering road alignments. Others survey the surrounding mountains and debate the scouring and disturbing winds. The wind rose (the plot of how often wind at different speeds comes from different directions) and the seeing rose (the corresponding plot of how good the seeing is as the wind comes from different directions) are imagined and debated. Jerry and George and Matthias are locked in discourse. They wish a few of these mountains were further away. But this is a world-class site by any reasoning. The devil will emerge in the details of our data.

Our visit to Cerro CH is complete. We will study this mountain and Paul and Eric rejoin us with visions of the road to build.

On that day, we had no permission to test on this peak. Our story, written on that day, would have left out the name of the peak. We had no rights and are required to apply for permits that are granted only when commercial, cultural, community and environmental issues are properly studied.

After our February visit, Bob Blum and our colleagues and supporters from our AURA and Chile partners carried out the application process. Meetings were held with agency officials, representatives of the regional government and residents of local villages. In one of the most touching moments since I joined TMT, Bob Blum described one in a series of meetings with indigenous residents in the villages of Socaire and Peine regarding permission for us to study Cerro CH. Bob described a rural meeting attended by 40 to 50 residents that included vigorous and detailed discussions of the project, satellite photos of the mountain and village boundaries and ended in a unanimous voice vote of “¡Sí!” Bob and his colleagues left with a sense that we had made new friends and that it we would find it rewarding to partner with the local residents in our work.

We threaded our way from Cerro CH, back to San Pedro, through meadows, by irrigation ditches and llamas and through the very villages that Bob will be visiting later as supplicant.

Mountain X

Our summit for the next day, departing from San Pedro, will remain nameless. We have not yet applied for permission. Until we obtain proper rights and fully respect the local sensitivities and laws, we must cloak its identity. But it is another 4000 meter class peak, as attractive as Cerro CH and in a different setting with respect to local mountain ranges. It may surpass Cerro CH we think, considering the winds that arrive from neighbors and bathe this candidate.

Our hoped testing location cannot be reached by Hilux at this site. We can only approach its pre-summit. Our stalwart team has visited on foot before, backpacking upward. Today we study from nearby and are most encouraged by the surroundings. We will bring our testing campaign here right after we mount Cerro CH.

Our caravan descends and travels to Calama for the night. Our last outpost. The great mining town and site of a gateway airport. WiFi service in the Park Hotel. The faint scent of return to civilization intrudes.


We want to make sure that our suite of studied mountains contains enough high mountain options. Mauna Kea is one. Cerro CH is another. And there is Mountain X. We want yet another high (4000 meter) or higher (5000 meter) option in the mix. As some of us prepare to return from Calama through Santiago to the US, others split up for a final day searching for insurance in the form of another high mountain.

Using the same screening that led us to our present sites, they set out with maps and GPS on a search. Not for the mountains (3 are on their list), but hoping just to identify roads through seeming roadless areas to our candidates. Roads to be traveled on following trips.

They travel all day on minor roads through tiny villages and do reach one mountain. The visit pays off but not in a way that was hoped. This mountain is too close to others. Winds from neighbors will disturb the seeing. The mountain is dropped from our list.

The second mountain eludes them. Fording streams and trying several dirt tracks with only hints from maps, they cross the roads off the list and do not succeed in finding the way to a summit that they can see taunting in the distance. Consolidating what has been learned that day, the expedition is declared completed.


There is no substitute for going there. The remoteness can only be appreciated by the trek. The vistas show a place that is not where we live.

Why do we go to such places? I have described a single event, a short and soft trip to this special place. I have called it a vacation. But we are sending a future generation of astronomy pioneers forward on a much longer visit to an outpost.

To live in the heady and rarefied atmosphere of humanity’s questions about the universe will require a generation of sojourn in one of these far and remote and dry and stark places. The special nature of nature here will be joined by the special nature of our inventions. Perfectly polished mirrors. Smooth and quiet and precise motors and drives. Laser light touching layers of the atmosphere and mathematical wizardry smoothing out the ripples to perfected clarity. All of this in cloudless dry and crystal nights far from intrusion and comfort.

email webmaster local users

Figure 1: A TMT site testing telescope on top of a 6 meter tower on Cerro Z. Note the closed fabric dome covering the telescope during the day. Gary Sanders studies the scene on the left. George Djorgovski enjoys the view as well.

Figure 2: The Cerro Z dome opened during the day, reveals the telescope against a cloudy sky. But daytime clouds do not matter.

Dear Reader: Though the first appearance of this article on the web included the names of the mountains that we are studying, we have received sage advice to drop the actual names. Thus, we have hidden the names behind monikers like Cerro Z and Mountain X. This regrettable departure from the openness of a project such as ours is motivated by the attention of land speculators who do not admire the images of the edge of the universe as much as they admire more worldly matters. Stripped of this detail, we hope that you will still feel the excitement of these remote and special places.

Figure 3: The expedition arrives on Cerro Z. Jerry Nelson (foreground), Paul Gillett (hat) and Eric Steinbring (red shirt) explore the summit and approach the telescope tower and sloped solar panels.

Figure 4: Matthias Scheock is at home on top of the tower.

Figure 5: Jerry Nelson (left), Bob Blum and Gary Sanders survey the surroundings and discuss the site.

Figure 6: The track up L. TMT equipment is just visible on the summit.

Figure 7: The undeveloped summit of Cerro CH.

The TMT project is a collaboration of Caltech, University of California (UC) and the Association of Canadian Universities for Research in Astronomy (ACURA). © Thirty Meter Telescope


Association of Canadian Universities for Research in Astronomy