24 March 2014 sky & telescopeMegatelescope Mirrors
The next generation of megatelescopes took an impor-
tant step closer to reality on October 23, 2012. That was
the day the University of Arizona’s Steward Observatory
Mirror Laboratory announced it had fi nished polishing
the fi rst mirror of the Giant Magellan Telescope (GMT),
to be built at Las Campanas, Chile.
A competitor in the race for the largest ground-based
optical telescope, GMT will combine seven 8.4-meter seg-
ments into a fl ower-like primary with the resolving power
of a single mirror 24.5 meters (80 feet) wide. The second-
ary mirror has the same design, with each of its seven
segments 3.25 meters wide; they will fl ex in real time
to tune out atmospheric distortions. The behemoth willHow to Build a
Construction of the world’s largest ground-based optical
telescope takes astronomical engineering to the next level.Robert
Zimmermandwarf the current generation of 8- to 10-meter ground-
based optical telescopes, and if its construction beats that
of the proposed Thirty Meter Telescope and the 39-meter
European Extremely Large Telescope, it will temporarily
be the largest in the world. (See the box on page 27 to see
how the GMT measures up to its competitors.)
Not only will GMT gather more light than any tele-
scope built so far, its corresponding sensitivity and resolu-
tion will result in deep images 10 times sharper than
Hubble’s. Equipped with this kind of next-generation
telescope, astronomers will delve into questions about
the formation of the fi rst galaxies and the nature of dark
energy and dark matter. They also hope to discover newGIANT MAGELLAN TELESCOPE / GMTO CORPORATIONGMT Mirror.indd 24 12/23/13 11:34 AM