There is a new international venture underway to build the world’s largest telescope. The telescope, which is to be housed high in the mountains of Chile, is called the Giant Magellan Telescope (GMT).
There are to be seven gigantic mirrors, each totaling 8.4 meters (27 feet) in diameter, which will operate together as a single telescope. The engineers among us will probably remark that it must be a challenge to build such big mirrors.
This is true, and is the case because as mirrors become so big they start to sag under their own weight until they eventually snap. There is a way around this problem, and the solution was found by scientists and optics engineers at the University of Arizona, led by Professor Roger Angel.
It turns out that a large single (monolithic) mirror can sustain its own weight if it is built into a special kind of honeycomb structure which is ultralight yet still incredibly strong. Glass blocks are placed by hand into a mold, and the mold is inserted onto a ‘lazy susan’ in an oven large enough to hold it. The lazy susan spins rapidly inside the oven unil the glass melts and fills the structure with approximately the desired shape.
After the glass cools it is then polished continuously for up to 2 years to work out all the bumps and to get the perfect shape, which for astronomers is an astounding 1 millionth of an inch.
For decades now Prof. Angel and his team have been successfully building telescope mirrors of various sizes, from the 1.8 meter diameter mirror comprising the Vatican Advanced Technology Telescope (VATT) on Mt. Graham to the seven 8.4 meter mirrors which will go into the GMT.
This action all takes place under the football stadium on University of Arizona campus. One is welcome to look into public tours of the lab the next time you are lucky enough to make it to Tucson.