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 Mirror 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 telescope mirror. 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 formation of stars, galaxies and black holes in the early universe.