World's most advanced mirror for giant telescope completed

October 23, 2012, University of Arizona
This shows the Giant Magellan Telescope, against the southern Milky Way, as it will appear when it's completed. Credit: Todd Mason/Mason Productions and GMTO Inc.

Scientists at the University of Arizona and in California have completed the most challenging large astronomical mirror ever made.

For the past several years, a group of optical scientists and engineers working at the UA Steward Observatory Laboratory underneath the UA's football stadium have been polishing an 8.4-meter (27 ½ feet) diameter mirror with an unusual, highly asymmetric shape.

By the standards used by optical scientists, the "degree of difficulty" for this mirror is 10 times that of any previous large . The mirror surface matches the desired prescription to a precision of 19 nanometers – so smooth that if it were the size of the continental U.S., the highest mountains would be little more than a half-inch high.

This mirror, and six more like it, will form the heart of the 25-meter Giant Magellan Telescope (GMT), providing more than 380 square meters, or 4,000 square feet, of light-collecting area. The Giant Magellan Telescope will lead a next generation of giant telescopes that will explore planets around other stars and the , galaxies and in the .

Buell Jannuzi, director of the UA Steward Observatory and professor of astronomy, said, "Making this first GMT mirror required all the expertise and experience that the University has built up over 25 years of making telescope mirrors and a great deal of innovation to push beyond previous limits in optical fabrication and testing. In achieving this remarkable milestone, the team built and demonstrated all the equipment and techniques that will lead to efficient production of the remaining mirrors for the GMT."

World's most advanced mirror for giant telescope completed
The first of seven mirrors for the Giant Magellan Telescope being polished at the UA Steward Observatory Mirror Laboratory. The polishing head, shown center, changes shape to match the curvature of the mirror as it moves across the surface. Credit: Ray Bertram/University of Arizona

The mirror was cast at the mirror lab from 20 tons of glass, melted in a rotating furnace until it flowed into a honeycomb mold. Once the glass had cooled and the mold material was removed, scientists at the lab used a series of fine abrasives to polish the mirror, checking its figure regularly using a number of precision optical tests.

The mirror has an unconventional shape because it is part of what ultimately will be a single 25-meter (82 feet) optical surface composed of seven circular segments, each 8.4 meters (27 ½ feet) in diameter.

The first of seven mirrors for the Giant Magellan Telescope after removal from the furnace. The back surface of the mirror is shown here during an inspection of the holes used to ventilate the mirror during operation in the telescope. Credit: Ray Bertram/University of Arizona

"We need to be certain the off-axis shape of this mirror, as well as the other six that will be made for GMT, is precisely right, to an accuracy of 1/20 of a wavelength of light," said Buddy Martin, polishing scientist at the Mirror Lab. "Only then will the seven large mirrors form a single, exquisitely sharp image when they all come together in the telescope in Chile. We have now demonstrated that we can fabricate the mirrors to the required accuracy for the telescope to work as designed."

The testing techniques, developed by Jim Burge, professor at the UA College of Optical Sciences, and his team, are a key part of the innovation enabling these giant off-axis mirrors. The second of seven mirrors for the GMT was cast at the mirror lab in January of this year; the third will be cast in August 2013.

The Giant Magellan Telescope will be located on a remote mountaintop in the Chilean Andes where the skies are clear and dark, far from any sources of light pollution. At the Carnegie Institution for Science's Las Campanas Observatory in northern Chile, earthmovers are completing the removal of 4 million cubic feet of rock to produce a flat platform for the telescope and its supporting buildings.

Wendy Freedman, chair of the GMT board, said: "The technical achievements at the UA's mirror lab and the dedication and commitment of our national and international partners will allow us to open a new window on the universe. An exciting future of discovery awaits us."

The telescope, slated to begin operations late in the decade, will allow astronomers and students across the U.S. and from around the world to address critical questions in cosmology, astrophysics and planetary science.

Matthew Colless, director of the Australian Astronomical Observatory, said, "The Giant Magellan has the potential to transform how we see the cosmos, and our place in it."

Explore further: First Giant Magellan Telescope Mirror Casting is 'Perfect'

Related Stories

First Giant Magellan Telescope Mirror Casting is 'Perfect'

October 28, 2005

The University of Arizona Steward Observatory Mirror Lab's casting of the first mirror for the Giant Magellan Telescope (GMT) "appears to be essentially perfect," UA Steward Observatory director Peter Strittmatter said after ...

Giant Magellan telescope site selected

October 4, 2007

The Giant Magellan Telescope (GMT) Consortium announces that the GMT will be constructed at Cerro Las Campanas, Chile. This location was selected for its high altitude, dry climate, dark skies, and unsurpassed seeing quality, ...

UA to shape solar telescope mirror

June 23, 2011

( -- When finished, the 4.2-meter mirror will be the largest telescope mirror ever pointed at the sun. Polished into a highly complex, asymmetric shape, it will be the centerpiece of the Advanced Technology Solar ...

Recommended for you

Neutron-star merger yields new puzzle for astrophysicists

January 18, 2018

The afterglow from the distant neutron-star merger detected last August has continued to brighten - much to the surprise of astrophysicists studying the aftermath of the massive collision that took place about 138 million ...

New technique for finding life on Mars

January 18, 2018

Researchers demonstrate for the first time the potential of existing technology to directly detect and characterize life on Mars and other planets. The study, published in Frontiers in Microbiology, used miniaturized scientific ...


Adjust slider to filter visible comments by rank

Display comments: newest first

3.5 / 5 (8) Oct 23, 2012
This telescope will never be completed due to Republican budget cuts.

Authorizing government to create telescopes is not part of the U.S. constitution, which as we all know is second only to the bible in it's holyness.

1.5 / 5 (12) Oct 23, 2012
Discovery at the cost of human life and misery, is not worth a dime. Everyday Americans kill, steal and lose their homes due to economic uncertainties, yet we see here those money are given to certain "educational institution" or certain scientist to live a happy life and look into the beyond. Not only these "discoveries," won't reduce the current misery of human beings, but everything that's achieved through these telescopes or their likes, will only benefit the rich. What a perfect system: Get from the poor and spend it in a way to help ONLY rich people.

Just as they exploit all the resources of this tiny world of ours, they will exploit everything to get rich. Finally, a discovery should be done ONLY the expense of the rich. If they want to mine the asteroids, they should first pay the REAL POOR people in Billions, then they should be allowed to exploit our solar resource.
2.4 / 5 (5) Oct 23, 2012
I thought people were curious about what lies beyond...
2.9 / 5 (7) Oct 23, 2012
If all the money in the world was pooled together and distributed evenly, it would only be a short matter of time before things went back to inequality. The basic problems with humanity are not solvable by us at this point in time. That does not mean everyone should stop learning about science or enjoying some form of luxury and that the world should stop spinning until we as a whole figure out how to be perfect, because it's going to be a long time in the waiting.

Great job for the people behind this project, incredibly exciting for a common person to sit back and watch this type of thing unfold.
2 / 5 (8) Oct 24, 2012
The basic problems with humanity are not solvable by us at this point in time.

We didn't invent truth and life. Truth and life save the world. Always has, does right now, and always will be.

We have more than enough now to end the current suffering.

The goal is not to do good. The goal is to do the most good. Anything less is an excuse.

Exploring space is not a problem. Lies and killing are the first manifestion of where the problem starts.
4 / 5 (2) Oct 24, 2012
working at the UA Steward Observatory Mirror Laboratory underneath the UA's football stadium

Damn. You don't get much more 'James Bond' than this.

What a perfect system: Get from the poor and spend it in a way to help ONLY rich people.

The universe is bigger than the 2 meters layer above ground of a planet measuring 13000km in diameter. Get used to it. And all that universe out there is
a) fascinating
b) potentially dangerous

So while it may seem OK to do a lot of navel gazing and just pool all our efforts into helping ourselves and each other it also denies any chance to reacting to any kind of danger from out there.
It also denies that what we find there can directly benefit all of us (e.g. forms of matter/energy interaction, special molecule formations, etc. )
If you want to look at it in a very short sighted manner - you are right. But humanity is here for the long haul (hopefully). We don't want to go the way of the dinosaurs.
3.7 / 5 (3) Oct 24, 2012
Funny that ChangBroot directs his outrage at low-paid scientists and doesn't mind the millionaires of this world who spend money on trivial things.

And before you say that they earned it, we live in a world where you earn money automatically simply by being rich (due to compound interest), and somehow it's considered normal; and there's also the cases of accumulating wealth through dishonesty or by inheritance. Until you point the finger at those dead weights on the backs of humanity, you can't say science is a waste of resources.
3 / 5 (6) Oct 27, 2012
I tend to hold curiosity as the highest virtue, because I define it as the pursuit of truth, and truth in turn as the set of all claims which accurately represent reality. A lot of people seem to think love is the highest virtue. Love has been watching helplessly as family members die of various diseases for a couple hundred thousand years. Curiosity empowers us to fight back. If you look back on human history and name those who left a positive mark on it, you will have a long list of curious people indeed.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.