What is GMT?

The Giant Magellan Telescope will be one member of the next class of super giant earth-based telescopes that promises to revolutionize our view and understanding of the universe. It will be constructed in the Las Campanas Observatory in Chile. Commissioning of the telescope is scheduled to begin in 2020.

The GMT has a unique design that offers several advantages. It is a segmented mirror telescope that employs seven of today’s largest stiff monolith mirrors as segments. Six off-axis 8.4 meter or 27-foot segments surround a central on-axis segment, forming a single optical surface with a collecting area of 24.5 meters, or 80 feet in diameter. The GMT will have a resolving power 10 times greater than the Hubble Space Telescope. The GMT project is the work of a distinguished international consortium of leading universities and science institutions.



How will it work?

Light from the edge of the universe will first reflect off of the seven primary mirrors, then reflect again off of the seven smaller secondary mirrors, and finally, down through the center primary mirror to the advanced CCD (charge coupled device) imaging cameras. There, the concentrated light will be measured to determine how far away objects are and what they are made of.

The GMT primary mirrors are made at the Steward Observatory Mirror Lab (SOML) in Tucson, Arizona. They are a marvel of modern engineering and glassmaking; each segment is curved to a very precise shape and polished to within a few wavelengths of light—approximately one-millionth of an inch. Although the GMT mirrors will represent a much larger array than any telescope, the total weight of the glass is far less than one might expect. This is accomplished by using a honeycomb mold whereby the finished glass is mostly hollow. The glass mold is placed inside a giant rotating oven where it is “spin cast,” giving the glass a natural parabolic shape. This greatly reduces the amount of grinding required to shape the glass and also reduces weight. Finally, since the giant mirrors are essentially hollow, they can be cooled with fans to help equalize them to the night air temperature, thus minimizing distortion from heat.

One of the most sophisticated engineering aspects of the telescope is what is known as “adaptive optics.” The telescope’s secondary mirrors are actually flexible. Under each secondary mirror surface, there are hundreds of actuators that will constantly adjust the mirrors to counteract atmospheric turbulence. These actuators, controlled by advanced computers, will transform twinkling stars into clear steady points of light. It is in this way that the GMT will offer images that are 10 times sharper than the Hubble Space Telescope.



The location of the GMT also offers a key advantage in terms of seeing through the atmosphere. Located in one of the highest and driest locations on earth, Chile’s Atacama Desert, the GMT will have spectacular conditions for more than 300 nights a year. Las Campanas Peak (“Cerro Las Campanas”), where the GMT will be located, has an altitude of over 2,550 meters or approximately 8,500 feet. The site is almost completely barren of vegetation due to lack of rainfall. The combination of seeing, number of clear nights, altitude, weather and vegetation make Las Campanas Peak an ideal location for the GMT.

More detailed information on scientific objectives and scientific instruments is available here.


Why is it being built?

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Most people do not realize that, as recently as 100 years ago, scientists thought the Milky Way was the entire universe.

But in the 1920s, Edwin Hubble, using the famous 100-inch telescope at Mount Wilson, determined that there were other galaxies too. That discovery was followed by the realization that the universe was expanding. These discoveries revolutionized our view of the universe. The heavens were not static, as had been assumed, but changing over time. Like the 100-inch telescope, perhaps the most exciting and intriguing fact is that the Giant Magellan Telescope promises to make discoveries that we cannot yet imagine.

Perhaps one of the most exciting questions yet to be answered is: are we alone? The Giant Magellan Telescope may help us answer that. Finding evidence of life on other planets would be a momentous discovery—certainly one of the greatest in the history of human exploration. But taking pictures of these so called “extrasolar” planets, which orbit other stars, is extraordinarily difficult. In addition to the vast distance—the very closest star to earth is four light-years away—the biggest problem is the glare of the host star which blocks out most of the reflected light of a small distant planet.


This is why the great collecting area of the GMT is so important. The GMT mirrors will collect more light than any telescope ever built and the resolution will be the best ever achieved.

This unprecedented light gathering ability and resolution will help with many other fascinating questions in 21st century astronomy. How did the first galaxies form? What are dark matter and dark energy that comprise most of our universe? How did stellar matter from the Big Bang congeal into what we see today? What is the fate of the universe?

More detailed information on the scientific objectives is available here.