Crews have begun to remove 3 million cubic feet of rock from a mountaintop in the Chilean Andes to make room for what will be the world’s largest telescope.

Sometimes life plays out in pleasantly surprising ways. Here, for example, is how Patrick McCarthy, director of what will be the world's largest optical telescope, watched explosives turn the summit of a Chilean peak to rubble — to ready it for construction — and then, a week later, how he unexpectedly found himself speaking to my high-school astronomy class in suburban Boston about the event.

This story begins on March 23rd, when astronomers and dignitaries trekked into the towering Andes northeast of La Serena, Chile, to a vantage overlooking the summit of Cerro Las Campanas. Topping out at 8,400 feet (2,550 m), this remote peak offers very dark skies, little or no risk of future light pollution, excellent atmospheric stability, and a high fraction of clear nights.

Blast atop Cerro Las Campanas in Chile

Explosives detonate atop Cerro Las Campanas in Chile on March 23, 2012, signaling the beginning of work to ready the site for the forthcoming Giant Magellan Telescope. Click on the image for a short Quicktime video of the blast.

Francisco Figueroa / GMTO

Cerro Las Campanas is where, in 2007, an international consortium chose to build the Giant Magellan Telescope. But 3 million cubic feet of the summit must be removed before construction can begin, so some serious demolition work is required. March 23rd's "big bang," which accidentally happened two minutes earlier than planned, is the first step in getting the site ready.

The GMT is one of several extremely large telescopes now on astronomers' drawing boards around the world — and it's the one closest to becoming a reality. (Don't confuse the GMT with the even bigger TMT, the Thirty Meter Telescope, which is destined for Mauna Kea but faces serious funding challenges and an uphill legal battle.)

Giant Magellan Telescope

When completed in 2020-21, the Giant Magellan Telescope will have an aperture of more than 83 feet (25 m) — making it the largest optical telescope in the world. For a sense of its scale, note the large truck depicted at lower right.


The GMT's design calls for seven enormous primary mirrors, each 27½ feet (8.4 m) across, arrayed in a tight cluster that will span more than 83 feet (25 m) edge to edge. When finished, the telescope's 1,000 tons of glass and steel, combined with adaptive-optics technology, will resolve target details down to 0.01 arcsecond, besting the Hubble Space Telescope's resolution tenfold.

I was going to write about all this a week ago. But the images and video made available at the time weren't very good, so I wanted to track down better ones. Also, some critical information on the GMT's website seemed a little dated. For example, I wondered, how could the project be moving toward construction when only 40% of its estimated $750 million cost has been raised to date?

It took a while to track down anyone in the know — all of the GMT's key officials were en route back to California from Chile. But by midweek Patrick McCarthy, the observatory's director, had gotten back to me. "The project has passed a number of critical milestones in recent months," McCarthy noted in an email. "These include successfully polishing the very ambitious off-axis figure in the first primary mirror segment, casting the second primary segment, starting work on the site, and selecting the first-generation of science instruments."

High-school lecture about GMT

Patrick McCarthy (far right) describes the Giant Magellan Telescope to high-school students at the Dexter and Southfield Schools in Brookline, Massachusetts.

J. Kelly Beatty

"I will be in Boston tomorrow," he added, not realizing that I live there. "Please feel free to call me on my cell if you would like to chat."

Well! Here was a chance to get details straight from the top. His willingness to chat soon turned into a planned face-to-face meeting. One thing led to another and, thanks to McCarthy's flexible schedule, not only did I get to interview him about the GMT but he also agreed to talk about it with my high-school astronomy class. A total win-win!

So what about the financing, I asked. McCarthy says the GMT's 10 institutional partners, anchored by Carnegie Institution of Washington, Harvard, MIT, University of Michigan, and University of Arizona, have raised just over $300 million to date, and he expects them to secure some large commitments later this year. He admits that it's risky to undertake activities like casting giant mirror blanks and blowing up a mountaintop without full funding, but he's confident that the remainder will be found. In fact, the board of directors for the Giant Magellan Telescope Organization just notified the U.S. National Science Foundation that it will not seek federal funding for the project.

Meanwhile, as McCarthy explained to my students, the GMT is proceeding in three phases: conceptual, detailed design, and construction. The project team (led by astrophysicist Wendy Freedman, director of Carnegie Observatories) has reached the second step, and the observatory's design will be finalized this year. "Now it's at the level of optimization," he explains, to capitalize on recent advances in electronics and other components. This overview is a good introduction to the GMT and its scientific potential.

First mirror blank for GMT

Member of the casting team at Steward Observatory Mirror Laboratory check the first primary mirror blank for the Giant Magellan Telescope after the furnace lid was removed October 21, 2005.

Lori Stiles / Univ. of Arizona

The summit of Cerro Las Campanas can be a little windy, so the design of the telescope's wide-open enclosure is being critically reviewed. Also tricky will be getting those seven giant eyes to work together. McCarthy says that ideally the primaries would have been hexagons, which could have been mounted edge to edge in order to create an unbroken collection area. But there's no way to trim the shape of optics so massive.

So when will all this come together? The plan is to have four mirrors feasting on starlight by 2018 and all seven in place by 2020 or 2021. The initial suite of instruments, still being negotiated among the GMT's partners, will probably involve two visible-light spectrographs and one for infrared work out to 5 microns. "We can go to 25 microns," McCarthy adds, thanks to the bone-dry climate that has made the Chilean Andes the top choice for southern-sky observing sites.

As for the impromptu lecture, I'm happy to report that my class proved an eager audience and asked some great questions. McCarthy enjoyed it too. "It is not often that I get to interact with young people — and particularly as bright a group as the students at your school."

Now, can I interest anyone from the Kepler mission to stop by?


Image of Martha


April 6, 2012 at 2:26 pm

Can someone explain to me how blowing off the top of a mountain in Chile is any different than blowing off the top of a mountain in West Virginia?

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Duke Briscoe

April 6, 2012 at 2:47 pm

@Martha: It looks like this is quite different than the W. VA. situations. This mountain is in a dry area, not likely involving threatening endangered species. It does not appear to be polluting or eliminating any waterways, or endangering nearby residents. 3 million cubic feet is probably smaller than coal mining operations.

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Anthony Barreiro

April 6, 2012 at 3:04 pm

Martha, I had a similar thought when I read the headline of this story and saw the picture. I'm curious if Chile requires anything like an environmental impact report for projects like this, and if so what environmental effects were predicted (Kelly, do you know?). Here are my immediate thoughts about the differences: [1] The mountains in West Virginia are very wet. The biggest problem with mountaintop removal coal mining is runoff that clogs the streams, kills all the fish, and permanently destroys the riparian environment. The mountains in Chile are bone dry. There's almost no rain, no runoff, and thus no creeks to ruin or fish to kill. [2] Coal is a non-renewable resource. When we burn up a ton of coal, we need to go find more coal, oil, or natural gas to keep the turbines spinning. (We should be using more renewable resources like solar and wind power, and greatly enhancing conservation and energy efficiency, but we're not there yet, in large part because of the stranglehold of the oil and coal companies on the US Government.) Astronomy, on the other hand, is a vastly renewable resource. If and when the GMT gets built, it will produce useful scientific data for many decades. I believe that we should be very skeptical about blowing the tops off any mountains, but in this case I would be willing to accept that the long-term benefits outweigh the environmental costs.

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Eric Eitreim

April 6, 2012 at 6:03 pm

Construction of the Large Synoptic Survey Telescope at Cerro Pachón is further along. Go to to see what it looks like after the top was leveled. They hired botanists to do a survey of the site prior to the explosion and removed all the native plants to a safe location to reintroduce them later. This link has pictures of them saving the plants:

I don't know exactly what all the Chilean regulations are, but all of these telescopes in Northern Chile are built in an "National Astronomical Preserve" similar to a National Wilderness Area here. No activity or construction is permitted that is not directly related to the activities and operation of the observatories. These Observatories are a good deal for Chile in terms of required partnerships with Chilean Universities and employment so Chile is protecting the advantage they have as a location for large telescopes.

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April 7, 2012 at 1:31 pm

Martha, your environmental awareness is laudable. I also agree with and welcome the reasoned responses of Duke, Anthony and Eric. This new telescopic endeavor is vastly different than what’s done in strip mining. 3 million cubic feet sounds like a lot, but in strip mining at times millions of cubic yards (27 cu. Ft/yard) are removed, leaving the huge gapping pits that that can be so disturbing. Here, only a relatively tiny fraction of the mountain is being leveled off, for reducing the height of the mountain is nether intended nor desired. We need high mountains for the excellent seeing they provide. I applaud the Chilean people for the environmentally responsible manner in which they are allowing some of their mountains to be used. I enjoy looking at a scenic mountain, but when I see one that is also crowned by an observatory my heart is warmed a little more, for now I know that mankind is being treated to a better view of God’s material creations.

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John Anderson

April 7, 2012 at 8:50 pm

People require heating, air conditioning, and lighting. Our culture and economy demand these needs be fulfilled at the risk of social unrest. If coal provides it cheaper than renewable sources, we can work hard to make renewable resources less costly, but don’t imagine we can just casually wish away the economic facts of life.

The head of NREL (National Renewable Energy Lab) was asked what he would do if he had more money in his budget. He responded that his need wasn’t money but more people with the scientific skills to do research. Pierre Hohenberg, Bell Labs director of theoretical physics in 1995, said that our best scientific minds are not going into the applied science of energy production and that there were too many ‘horses to ride’, that is to say there is a disjointed set of potential technologies such as hydrogen, wind, solar, fusion, fission, and so on. It is not considered a ‘sexy’ field to go into so the top young minds don’t.

So if we want to make coal obsolete in this century, maybe we should tap some of the best people to make a sacrifice and contribute some of their time to applied science projects such as ITER, the National Ignition Facility, and other breakthrough technologies both in government funded research and privately funded research. I would like to see people of the caliber of Ed Witten, Frank Wilczek, Sean Carroll, and Adam Riess tackle some of the issues surrounding new energy generation technologies.

There is much improvement to be done in alternative/renewable energy before we can put coal in the same category as flint tools.

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John W.

April 10, 2012 at 11:14 am

Whew--lighten up! To think that we will have in our lifetimes a telescope that would have been only a dream a generation ago is something to be celebrated! Let's not try and find the devil in the details just yet--they'll have enough of that just getting this built. Best of luck to all involved--all of humanity for all time hence will benefit when this is built--the discoveries are only to be imagined. Can't wait till all 7 mirrors are in place--my only complaint is that it will take as long as it will. Again, good luck and thanks for doing all this for all of us.

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April 11, 2012 at 5:09 pm

Well said, John W. We've been so quick to assuage environmental concerns that we're overlooking this great news. Thanks for putting the discussion back on the right track.

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