Giant Magellan Telescope (GMT)

The GMT in Chile is slated for completion in the late 2020s. It will become the largest optical observatory in the world, with 10x the resolving power of the Hubble Space Telescope, and will be able to see objects farther and smaller than ever before.

The Giant Magellan Telescope (GMT), slated for completion in the late 2020s, will be one of the world’s next giant earth-based telescopes, with 10 times the resolving power of the Hubble Space Telescope. For example, if the telescope were located in Phoenix and pointed at Tucson, one could see the torch on a dime from Tucson.

It will be constructed in the Las Campanas Observatory in Chile, one of the places least affected by light pollution in the world and subsequently one of the best spots on Earth for long-term astronomical observation. Located in one of the highest and driest locations on earth, the GMT will have spectacular conditions for more than 300 nights a year.

The telescope represents a collaboration between a distinguished, international consortium of leading universities and institutions, including the University of Arizona, which has made a $60 million commitment to the GMT project, ensuring access for UA astronomers to valuable observing time on the landmark telescope.


Giant Magellan Telescope mirror cleaning before the grinding and polishing begins
Giant Magellan Telescope mirror cleaning before the grinding and polishing begins

The GMT will also employ seven of today’s largest mirror segments, each created by the UA’s Richard F. Caris Mirror Lab and weighing 25,000 pounds, or 12 and a half tons. The first of these mirrors was cast in 2005, and the latest in 2021. The Mirror Lab will also produce an eighth, backup mirror.

With these mirrors, the GMT will revolutionize our current understanding of the universe.

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 imaging cameras. There, the light will be measured to determine how far away objects are and what they are made of.

The primary mirrors built by the UA’s Mirror Lab are a marvel of modern engineering and glassmaking; each segment is curved to a very precise shape and polished to within a wavelength 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.

The mirrors cool gradually, over the course of about 12 weeks, ensuring that they don’t break. Grinding and polishing each mirror can take years. The surface is polished so precisely that if the mirror were expanded to the size of the United States, the highest and lowest points would differ by no more than half an inch.

With its unprecedented light gathering ability and resolution, the GMT will help to answer one of the biggest questions in science today: Is there life outside of the Milky Way?