Science AMA Series: I’m Dr. Robert N. Shelton, president of the Giant Magellan Telescope Organization (GMTO). I’m here with my colleague Dr. Patrick McCarthy, director of GMTO and eminent astrophysicist, to talk about what it takes to build the world’s largest telescope. AMA!


Hi Redditors, we are Robert N. Shelton and Patrick McCarthy, and we’re here to talk about what it takes to build the world’s largest telescope with all of you today. The Giant Magellan Telescope (GMT) will image planets around other stars (including our nearest neighbor Proxima b), probe their atmospheres for signs of biological activity, and look back to the epoch of “first light” - the period shortly after the Big Bang when the first stars, galaxies and black holes formed. To get started, please allow us to introduce ourselves.

Robert is the president of Giant Magellan Telescope Organization (GMTO). He is leading the ambitious group behind the GMT as they take the telescope from a bold vision to a world leading research facility. Before joining GMTO, Robert was the president of Research Corporation for Science Advancement, America’s first foundation dedicated solely to funding science. In his earlier days, he also served as the executive director of the Arizona Sports Foundation, the 19th president of the University of Arizona, and many other leadership positions at well-known universities. Robert has a Ph.D. in physics and is an experimental condensed-matter physicist focusing on collective electron effects in novel materials.

Patrick is the director of GMTO and leads the team of scientists and engineers building the GMT. An accomplished astronomer, Patrick is best known for his work observing the formation of the earliest galaxies and his study of distant low frequency cosmic radio sources. After completing his Ph.D. at the University of California at Berkeley, Patrick joined the Carnegie Observatories as a Carnegie Fellow and a Hubble Fellow, and then became a faculty member at Carnegie. He was part of the team that developed the last, and most powerful, instrument to be deployed on the Hubble Space Telescope, the Wide Field Camera 3.


The GMT is slated to be the first in a new class of giant ground-based telescope, capable of producing images with 10 times the clarity of those captured by the Hubble Space Telescope. Powered by the joined forces from a global consortium of top universities and institutions, the GMT aims to discover not only the answer to the question “are we alone?” but also to answer questions we don’t yet know to ask.

As you may know, big science projects like the GMT face a range of challenges that come in many flavors. Just as Rome wasn’t built in a day, it will take a lot to build the world’s largest telescope, and we are here to share with you what we have learned so far. We've seen a lot of great questions and will start to answer now. Ask us anything!

Edit: 4PM, EDT
That’s all, folks! We have had a great time chatting about what it takes to build the world’s largest telescope. Appreciate all of your interesting and thought-provoking questions. To keep up-to-date on our recent developments or new job postings, be sure to follow us on Facebook (@GMTelescope), LinkedIn (Giant Magellan Telescope Organization), Twitter (@GMTelescope) and Instagram (@gmtelescope). Until next time. – Robert & Pat

How do you get better-than-Hubble clarity with a ground-based telescope? How much better clarity would you get if you could somehow build GMT in space (either free floating or on say at a lunar pole)?


Answered by Pat:

The angular resolution of a telescope is set by the diameter of the primary aperture and the wavelength of light used during the observation. The GMT’s primary mirror is ten times larger than that of Hubble, thus we can produce images that are ten times sharper, when observing at the same wavelengths. The caveat is that when observing from the ground we must correct for the image distortions introduced by the Earth’s atmosphere. This is done through a technique called “adaptive optics” and is most effective in the red and infrared regions of the spectrum.

If we put GMT in space we would get the same image clarity as we get on the ground with adaptive optics, but we could probably observe at shorter (blue and ultraviolet) wavelengths and get sharper images. Putting a telescope on the lunar pole is an attractive idea. One would put the telescope in a deep crater that is always in the shade. The advantage is that the telescope would get very cold and would thus be more sensitive in the far infrared. The Webb Space telescope is a free flier and its sun shield will allow it to cool to even lower temperatures than one would get in a lunar crater. There is ice in the bottom of some of the lunar craters, so one would have to take care in selecting a good spot!

Till what distance and angular separation can this telescope resolve?

Thanks for AMA


Answered by Pat:

The GMT’s angular resolution is 10 milliarcseconds (3 millionths of a degree!) when measuring at a wavelength of 1 micron. In practical terms this means you could resolve a dime at 100 miles but of course astronomers are interested in celestial applications.

In the study of exoplanets we can easily separate the closest exoplanet to our solar system (Proxima b) from its parent star. We will also be able to resolve the sphere of influence (the area in which the gravitational pull from the black hole dominates) around black holes and other galaxies and thus measure their masses.

The distance at which the GMT will be able to take good data is measured in time from the Big Bang – so we expect the GMT to be able to see back as far as 100 million years after the Big Bang.

If you were a photon entering the lens, what would your path look like as you traveled through the telescope?


Answered by a photon:

Large telescopes are built primarily around mirrors rather than lenses, but your question is a good one nonetheless. I’m a photon traveling from a distant star or galaxy and I first have to make my way through the Earth’s atmosphere. My path may be bent and phase may delayed as I travel through atmospheric layers with different temperatures and densities. After reaching the telescope my photon self would first bounce off one of the primary mirror segments and make a nearly 160 degree turn. I would then hit and bounce off one of the secondary mirror segments and make a 180 degree turn and then travel towards the center of the telescope. I then encounter a flat mirror and take a 90 degree turn heading towards a science instrument. In the case of an infrared instrument I would pass through a flat piece of pure sapphire and into a cold vacuum inside the instrument. From there I bounce around like a pinball among the internal camera optics before reaching the detector! Once inside the detector material I then travel through the crystal lattice until I encounter an electron that will bump out of its place in the crystal. At that point I have done my job and the electron I kicked out will be collected and counted as part of the “image” produced by the telescope.

Some of the photons that GMT expects to capture will have travelled for 10 billion years, but its trip through the telescope will last a few microseconds!

Who actually designs and builds the telescope? Obviously the field of science attracts so many excellent engineers, but it intuitively seems far fetched to allow someone with little experience in actually building them to design a multi-million dollar assembly. In my head I anticipate a company or group of them who have done this before, and you guys sit down with them and work with their experienced teams to create the vision you have. How close is that to the truth?


Answered by Robert:

The design of the telescope is accomplished through multiple components; for example, mirrors, enclosure, electronics, specialized instruments, and more. Each component is the responsibility of a team of engineers with extensive experience. Many of our staff have been engaged in development of prior generations of telescopes, both on the ground and in space.

The overall specifications are driven, of course, by the scientific goals for the telescope. This complex array of processes is coordinated by the project manager and project scientist. In addition to the in-house engineers and scientists, we contract with external organizations for some of the work. At each stage of design and development, we engage external reviewers with expertise from the world-wide astronomy community to review and analyze our designs. For the major procurements, such as the mount that holds all the mirrors and instruments or the observatory structure itself, we conduct a competitive bidding process.

How does one of these telescopes compare to one I can buy at a shop for recreational use?

And what's the price of one of these?


Robert: First, thanks to /u/GrizzlyAP97 for the current cost for an 8-inch telescope. The basic optical principles are similar to an 8-inch Cassegrain telescope. When I had young children at home, I recall using a similar-sized telescope to further their interests in science. Astronomy has a unique (perhaps along with children’s fascination with dinosaurs!) role in attracting young folks to science. Those children from past generations are the ones leading us these days as more powerful observatories are planned, built and employed. For the GMT, the Board of Directors has authorized a cost of approximately $1.05 billion (US); a bit of an increase over the one I used with my family!

Can you explain what types of cameras/sensors this telescope will utilize. Also will the optics be designed for visual light or near IR/IR?


The telescope will use a variety of instruments – some of which will be cameras. The main workhorse instruments will be spectrographs of different kinds. These disperse the light into its constituent colors much in the way a prism does. This allows us to measure properties such as the chemical composition, redshift and internal motions through the Doppler shift. Our instruments will span from the blue end of the visible wavelengths (0.3 microns) to the far infrared at 20 microns. The visible light instruments will use silicon based charge-coupled device detectors while the infrared instruments will use HgCdTe detectors.

The cameras work in tandem with state of the art wavefront sensors that use infrared sensitive avalanche photodiodes and other photon counting sensors.

What can this telescope do than the Hubble or Webb can't?


Hubble has produced incredible images of depth and clarity and the Webb telescope will have unrivaled sensitivity in the infrared. GMT will have angular resolution that cannot be matched by space telescopes currently under development. This will be particularly powerful when studying planets around other stars and “weighing” black holes in other galaxies. The largest telescopes on the ground today work collaboratively with the Hubble; we expect to do the same with the Webb telescope.

I'm not a person really knowledgeable in physics (I wish I was, physics has always amazed me), but I'm interested in how the optics for your telescope will work. Is it practical to use the same optics as a standard scope (glass magnifying lens), or does something special need to be done? I think that would be a lot of glass at large sizes, I feel like there almost has to be a unique/more practical​ way of doing that.

Thank you for the AMA, I'm really glad scientists like you two are taking your time to directly interact with the public. It benefits everyone.


Answered by Pat:

Glass lenses were used to make telescopes from the time of Galileo until the late 1800’s. Lenses reach their largest practical size at around 1 meter, or 40 inches, in diameter. It is difficult to make uniform transparent glass larger than this size and the focal length of the lenses makes the telescopes very impractical (see this example of an unwieldy telescope!). Modern telescopes are “reflectors” based on mirrors. Mirrors can be made larger and more steeply curved than lenses (the light only needs to bounce off the surface rather than travel through the glass). Mirrors also have a largest practical size – roughly 8.5 meters or 28 feet in diameter. For giant telescopes like the GMT we must piece together several mirrors to make a large aperture. The first telescopes to do this were the Multiple Mirror Telescope and the Keck telescopes. The GMT will use seven mirror segments, each one 8.4 meters in diameter - the maximum size that can be manufactured and transported to the mountain top in Chile. The optical physics involved is simple, but the details of making and testing the mirrors requires great expertise in optical science. We are fortunate to have a world leading team of optical scientists at the University of Arizona leading the development of the GMT optics.

What is the most interesting thing that either of you have observed using the telescope?

Are you two excited for the James Webb?


Answered by Pat: The GMT is not ready for use yet! As to my most interesting observation, it happened many years ago. I was observing a distant radio source when I noticed a strange object on my spectrum. A little thought and quick calculation revealed that it was the most distant quasar ever seen (redshift of 4.4) at that time! I hope to use GMT to push back the high redshift frontiers to z = 10 and beyond. It takes a large telescope to see back to when the Universe was only 100 million years old.

We are both excited about the James Webb telescope.

Thank you doctors, and the entire Magellan team for the hard work you're doing to expand human knowledge, and for this AMA.

What will be the resolving power of the Magellan telescope when it comes online? Will you be able to resolve any details of Earth-sized worlds?

Will you rely on exoplanets passing in front of their stars for spectral data, or do you anticipate being able to sample their spectra using the light they reflect from their parent star?

Finally, how large of a telescope would it take (and how precise of a starshade) to image continents on an Earth sized world 30 light years distant?


The resolving power of the telescope is discussed in our answer to /u/arj98. While we will be able to separate the light of the planet from its parent star, no telescope under discussion today will resolve the planets themselves or reveal their structure. You are quite correct in noting that we will use spectroscopy to study the properties of the atmospheres and surfaces of exoplanets. There are two approaches – when the planet passes in front of the star (transit) we can sample its atmosphere through absorption. When the planet passes behind the star (eclipse) we can sample the planet light via reflection by subtracting the spectrum of the star with the planet and the star alone. This requires a high precision spectrograph – and we are building just such an instrument for GMT.

The star shade concept being developed by NASA is fascinating and it will allow one to work in closer to the star, but will not allow us to image the planets directly. That will have to wait for another generation!

When the telescope is complete, who is/are the first to see the images it's able to produce?


Answered by Robert:

GMT’s Science Advisory Committee will be working on this question in the coming years.

In terms of when we get images, the telescope will undergo commissioning for a period of months. When the telescope is aligned and commissioned, the first light image will be taken. There will be no doubt some processing required but I would hope it would be a matter of days or weeks after first light before we could release it.

Philosophical question: will man ever colonize Mars?


Robert: From my perspective, this question deals more with the priorities of humankind and the necessary sustained commitment required for any project of this magnitude. I think that if the scientific and technical interests in colonizing Mars become coincident with humankind’s need to explore, then we will establish colonies on Mars.

Pat: I’m not going!

How hard is the development of the adaptive optics for this telescope? Are the systems designed for smaller telescope usable, or do you need larger devices? How many distances are they imaged to, and how is the imaging done? I'm a lens designer, and curious.


Answered by Pat:

The development of the adaptive optics (AO) for the GMT is indeed a challenge. Fortunately, we can build on the experience gained in developing AO systems for smaller telescopes. Our system uses “rubber mirrors” located at the second reflection in the telescope (the secondary mirror). The “rubber” or deformable mirror is only 2 mm thick and its shape is controlled through force actuators using permanent magnets and voice coils – similar to conventional loud speakers. We will use a total 4700 voice coil actuators to control the mirror surface with a control frequency of 1 kHz. This allows us to correct for atmospheric distortions at wavelengths as short as half a micron.

The GMT AO system builds on the heritage of the systems in use on the Multiple Mirror Telescope and the Large Binocular Telescope.

My question is for Robert. Can you discuss your interesting career trajectory and what you deem to be the key turning points/decisions therein that brought you to where you are today? What pitfalls have you seen that might not be so obvious to early career scientists?


I have been fortunate in my career because of the many and varied opportunities that came my way. In a sense, I think this type of career path is even more typical for the younger generation as they understand that a broad-based educational background affords flexibility and new ways to grow in knowledge and experience. In my case, the fundamental nature of a physics degree and a great interest in people have been the key factors.

In retrospect, there were two inflection points in my career. The first came when I accepted the position as chair of a physics department, thus committing myself to learning about the inner workings of higher education. Would I find this new challenge interesting, or just a frustrating bureaucracy? Actually, some of both! However, my path to leadership positions was set and wonderfully so as I met extraordinary individuals working well outside my own areas of expertise.

The second turning point came when I departed higher education to lead not-for-profit organizations whose missions I could embrace. That decision brought me to the GMTO Corporation. You asked about “pitfalls” and rightly so. Looking back, I know that each new position, each new challenge had pitfalls – some I negotiated well, others I had to admit to less-than-optimal outcomes. But in each position, I learned from those around me and gained increasing experience and confidence for the next set of opportunities.

Many space telescopes seem to be built for a specific mission, does the GMT have a specific mission or is this more of a general (albeit giant) telescope?


Answered by Pat:

The GMT is a general purpose telescope with a broad science mission. Our highest priority missions are the study of planets around other stars and, in particular, Earth-like planets. The GMT will allow us to probe the atmospheres of exoplanets and to study their orbital dynamics in detail.

Our second key mission is to look back in time to see the “first light” in the Universe. We expect that the first stars and galaxies lit up the Universe some 100 million years after the Big Bang. The GMT will allow us to detect the light from these first stars and galaxies and understand their chemistry and the types of stars that they are forming.

Scientists at our partner institutions will also propose cutting edge experiments and observations that address the forefront questions of the day.

Greetings doctors,

Hi! Its super cool to get to interact with you guys. I'm currently working on a novella that is set in and around the GMT, and it deals with the hypernova of Eta Carinae (hence the name.) I thought this would be a perfect time to ask a few questions to which I can't find the answers online: What is the height of the telescope housing? What is the purpose of the building on the same hilltop as the GMT? How many people will be at the GMT site on average? How many of those will be astronomers? Around what year will all 7 mirrors be installed?

Thanks billions and billions, as Carl Sagan would say.


The height of the telescope housing (the dome!) is 63 meters (206 ft). There will be two other buildings on the top of the mountain - a construction office and a laboratory. The laboratory will be used to recoat the primary mirrors and to service and upgrade instrumentation.

During operations we expect to have a staff of 60 people on the mountain, several of which will be GMTO astronomers. Visiting astronomers who come to use the telescope will stay on the mountain. We expect that on any given night there will be several astronomers on the mountain doing research and collaborating with the technical and operations staff. During the construction phase we will have between 75 and 250 people on the site. Regarding your last question, our schedule shows all seven mirrors installed in the telescope by 2025.

Good luck with your novella – we are all waiting for Eta Carinae to explode!

How would I go about getting into the astronomy job market? I am extremely fascinated with this field. I do not have a degree, but I have listened to all of Richard Pogge's lectures from his Ohio State astronomy courses. I also, am enrolling in a college level astronomy class.


Robert: First, kudos for enrolling in the astronomy class. This is an important step in learning the vocabulary and being exposed to the excitement of astronomy. If you wish to be an astronomer you need to study physics and mathematics and go to graduate school in astronomy or physics. There are, however, many pathways to a career in space-related industries. Observatories and telescope projects are always looking for qualified engineers, computer scientists, data analysts, and tech-savvy people with the desire to learn and make a difference.

At GMT we employ mechanical, optical, electrical, and systems engineers, as well as all combinations of those (e.g. opto-mechanical engineers!). We also employ project managers and people who are responsible for organizing the schedule.

If you don’t like this idea, and don’t want to do astrophysics, then you can still work on telescopes – telescope building projects and working observatories need financial people, administrators, outreach people, HR people and so on.

Pat: I went to graduate school at the same time as Richard and we spent many nights observing on Mt Hamilton together. He’s a brilliant guy and his lectures are outstanding.

If you didn't have to follow rules or program criteria. And could just use the GMT as you wish, what's the first thing you'd personally want to look at through it?


Answered by Robert: From my physics background, I have a keen interest in using the GMT to look back in time to understand the formation of the earliest galaxies. However, in all candor, I would yield to my more comprehensive inquisitive personality and focus on the earth-like planets most likely to support life as we conceive of it. I would want a thorough chemical analysis of its atmosphere – diatomic oxygen? methane? carbon dioxide? water vapor?

Thanks to both of you for you dedication to human understanding of our universe and our place in it. I'm immensely excited to see the first picture in the early 2020s(?).

How real is the threat that technology plays to a structure like GMTO?

I understand this project is going to be huge and unique, but is there a possibility that by the time it is constructed a leap in technology or more efficient use of existing technology could give us approximate results?


The advances in technology that will occur during the design and operation of the GMT will be of benefit to the observatory (we expect to see first light in 2023). One advantage of a ground-based telescope with an anticipated lifetime of 50 years is precisely the opportunity to incorporate new technology. This can be done readily as new instruments are designed, built and incorporated in the telescope. One might think of the telescope as a highly sophisticated device to collect light, while each new generation of the instruments (spectrographs, cameras, etc.) will use the latest technologies.

Are the matinence costs of the telescopes high? Like when some dust settles on the lens of a home telescope you just wipe it off, I imagine this would be a lot more difficult on such a larger scale.


We have a well-developed operations plan and budget. Most observatories spend the equivalent of 5-7% of their capital construction costs each year for operations. We expect to employ roughly 120 people during the operations phase. Some of these will be engaged in cleaning and periodically re-coating the mirrors. We will clean the mirrors with CO2 snow a few times each week (you’re right – we can’t just wipe the dust off!). Once a year we will wash each mirror with deionized water and every other year we remove the aluminum coating and apply a new coating in our large vacuum chamber.

Check out this YouTube video of the re-coating of the Magellan telescope mirror (a smaller telescope at the same observatory site as the GMT).

Can your telescope see other galaxies?


Billions and billions of them! We should be able to study nearby galaxies in great detail and observe distant galaxies when the universe was less than a billion years old.

Who funds the frontiers of astrophysics research? From the outside looking in, it seems that y'all would be constantly hurting for federal grants, considering you don't even get a 10th of what the military gets in support.


Answered by Robert:

The GMT currently focuses on private funding from the 11 founding institutions, consisting of U.S. universities and research institutions and their counterparts in Australia, Brazil and Korea. Of course, Chile is a key partner as the host country. This emphasis on private funding provides a degree of flexibility that is important at the early stage of the project.

Turning to the larger question you pose about astrophysics research overall, funding for research projects and telescope time comes primarily through federal agencies such as the NSF, NASA and the Department of Energy. Historically, farsighted individuals have supported astronomy, e.g. Andrew Carnegie, The Rockefeller Foundation, the Ford Foundation, the Keck Foundation, and other philanthropic organizations.

Do you make mirror that reflect better/magnifying or just bigger one ?


/u/blablabliam is right – the reflectivity of mirrors can now be made better than 90%. So, the only route is to make larger mirrors! Keeping the mirrors shiny is a challenge. New coatings are lasting longer than those from past generations and cleaning techniques allow us to keep the reflectively levels high for long periods of time.

Have you ever encountered a case in which the Paper or a Journal you were following during your R&D turned out to be not so accurate and in the end you had to redo most of the parts of the project that you were working on?


Answered by Robert: Yes. Scientific research is constantly evolving, with new publications improving or in some cases correcting prior work. The peer-review system allows for this self-correcting mechanism as researchers expose their work to be analyzed and replicated or refuted by others. In my discipline of condensed-matter physics, I have had occasions to revise experiments based on new data and theories. Frequently, my revised experiments led to new discoveries of materials and their unique properties.

Will the telescope primarily be used for large surveys or will people be able to write proposals and receive time on it? I'm interested in studying the rotation curves of high redshift spiral galaxies and currently we can only get to about z < 3 with current telescopes (like large binocular telescope in Arizona).


We expect that there will be a mix of large surveys or “Key Projects” and smaller individual investigator programs. All of the observing time will be assigned based on peer-review of proposals from scientists interesting in using the telescope.

We too are very interested in the rotation curves of galaxies at high redshifts. This is a great way to probe their dark matter content and merger history. As you note, current telescopes are limited to z < 3 and even there they struggle. These observations are “photon starved” – there just is not enough light to divide it up by spatial element and wavelength and still have good statistics in the presence of detector noise. The GMT and other “Extremely Large Telescopes” will deliver enough light to the spectrographs to allow us to make these observations with excellent sensitivity. Great question!

Hello! Is your organisation international? And if so how is the work divided between different teams? Also, are there new breakthroughs related to large ground-based telescope like this one? Thank you by advance! Edit : what would be the minimum magnitude that is needed for a star to be seen with this telescope?


Answered by Robert and Pat:

Yes we are indeed an international organization – it takes a large and diverse team to build a telescope as large and complex at the GMT. Scientists at our partner institutions are developing scientific instruments for the telescope and some of the critical optical and mechanical subsystems needed to ensure that the telescope produces the best possible images. Our Scientific Advisory Committee – drawn from expert scientists at all of our partner institutions – set priorities for the development of scientific instruments. At present we have expert teams in Australia, Korea and Sao Paulo, Brazil working on the design of state-of-the-art cameras and spectrographs for the GMT. Scientists at our U.S. partners are developing the optics and the sensors at the heart of the telescope.

There are a number technical breakthroughs associated with the construction of the telescope (e.g. adaptive optics, off-axis optics), but the big breakthroughs will be scientific in nature. These usually cannot be anticipated in advance!

Regarding the faintest magnitude objects that we can see – we expect to observe stars and galaxies down to 28th magnitude with long exposures!

I know you guys like glass to make telescopes, where does the best glass come from? Also does the thought that you are using glass (which is made from sand, which is made from tiny dead animals' shells from a long time ago) to make something to allow us to look back in time, kinda freak you out?

Do you think you could look so far back in time that you could see one of the animals that made the shell that the sand was made of that the lense for the telescope was made of?


Pat: Glass is a great material for making lenses and mirrors. We use a special type of glass that has a very low rate of expansion as temperature changes. The glass is indeed made from sand, but not from sand that contains shells or coral. The sand used to make glass comes from quartz rocks that have weathered and decomposed into fine grains. Our glass contains small amounts of Boron and other chemicals added to give it just the right mix of properties.

If we were looking at an exact Earth analog (around a G-type star) with your telescope from 5, 20, and 50 light years away, what could we reliably sense from the spectra of that planet?

Free oxygen? Methane? Chlorophyll? Surface temperature? Any other life evidence?


Pat: Earth analogs are a challenge, but our best opportunities are from rocky planets that transit in front of their parent stars. Transmission spectroscopy is our best approach to studying the atmospheres. The tracers that we are most interested in are Oxygen (O2), Methane (CH4) and Carbon Dioxide (CO2). A high concentration of O2 is a good indicator of biochemistry – but not entirely conclusive. The simultaneous presence of O2 and CH4 is very strong evidence for biological rather than geochemical processes. I’m afraid that Chlorophyll is a big challenge.

Changing brightness and colors on exoplanets observed through imaging can also be powerful diagnostics. Specular reflections from oceans have a distinctive phase function while scattering from high clouds produces spectral features that can be detected with high signal-to-noise observations.

Check out this planet – it could be the perfect target for searches for life:

For those of us who are amateur astronomers/astrophotographers can you give us some basic stats on this telescope? What is the focal length, f ratio, FOV, pixel scale? Sorry I've asked a couple of questions but how often do you get a chance to talk to people building the worlds biggest telescope?!


Answered by Pat:

The primary mirror array has a focal length of 18 meters and an f-ratio of 0.7. The final focal length is 196 meters and the focal ratio is f/8 and the scale at the focal plane is 1 arcsecond (1/3600 of a degree) per millimeter. Our cameras use reimaging optics to produce pixel scales that range from as fine as 8 milli-arcseconds for the AO instruments, to 0.15 arc seconds for the visible light instruments. The field of view of the telescope is 20 arcminutes – a bit under the size of the full moon. The correcting lenses needed to produce sharp images over this field are large – just over one meter in diameter!

Just after first light, will science research take place? Or will it mostly be alignment and calibration? Who has first "dibs" on science observation, and do you know if there is any specific research already intended for GMTO?


As a telescope is commissioned, there is always a mix of calibration activities and science observations. Access to the telescope will be based on a formal proposal process. All proposals will be reviewed by a panel of expert astronomers; only the most meritorious proposals will lead to access to the telescope. We expect that the demand for time on the telescope will exceed the available number of nights in any year by roughly a factor of 10!

While we have identified a number of high priority research fields, the peer-review panels will have the final say in what observations are carried out at the telescope.

"To talk about what it takes to build the worlds largest telescope."

So, you're here to talk about money... lots of money.

I'll bite, what's the current estimate on the total cost of the project?


Creating the largest telescope in history is a monumental endeavor, and this will be the largest privately-funded telescope initiative to date. The project is supported by a world-wide consortium of partner institutions including the Australian National University, Astronomy Australia Ltd, Carnegie Institution for Science, Harvard University, Korea Astronomy and Space Science Institute, the Smithsonian Institution, the University of Arizona, the University of Texas at Austin, Texas A&M University, the University of Chicago, and the São Paulo Research Foundation (FAPESP). The Board of Directors has capped the cost of the project at $1.05 billion (US), accounting for inflation.

Because the early universe is traveling so quickly away from us, the redshift pushes these objects into the infrared, which telescope should be able to see further back? GMT or JW?


The redshift does move many of the spectral features into the infrared. The Webb will be very powerful in studying features that are normally seen in the visible part of the spectrum but are redshifted into the 2-5 micron region of the spectrum. GMT will be particularly powerful in observing spectral features from the vacuum ultraviolet that are redshifted into near-infrared (0.8 to 2.0 microns). If the era of “first light” is indeed around z = 10, the GMT will be a particularly powerful tool for observing ionized Hydrogen in early galaxies. Undoubtedly, the GMT and Webb will be a powerful combination for exploring the early Universe.

What are the benefits of being a privately led science project? How do you fund something like this?


Answered by Robert:

A privately led science project such as the GMT has the great advantage of drawing on the enthusiastic commitment of its Founders. Our member organizations joined GMT because of their passion for the project. That passion translates into their bringing intellectual and technical resources (as well as vital financial support) to bear on the challenge of building the world’s largest telescope. That said, we still face the same challenge of any new, massive scientific/engineering project – securing the necessary funds. We approach this challenge through our Founders and the multiple connections they have. They are the backbone of our organization.

Can you explain how we know the Universe's age if there is no universal frame of reference?


The age of the Universe can be determined from measuring the current rate of expansion (the Hubble Constant) and the rate at which the expansion has changed over time. Scientists have spent decades determining these parameters with high precision and we can now say with great confidence that the age of the Universe is 13.4 billion years. This age is the time since the Big Bang – the time when the Universe had an infinite density.

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