Optical telescopes that offer game-changing views of stars, nebulae and exoplanets require just as much engineering ingenuity as dams, tunnels and bridges. For example, the primary mirror of the Subaru Telescope, which sits at the summit of Mauna Kea in Hawaii, has a diameter of 27 feet (8.2 meters) and weighs more than 25 tons. The structure supporting the optics and the enclosure surrounding the entire system rival any building in terms of complexity.
One of the biggest challenges with traditional telescopes is getting the mirror to the top of a mountain without breaking it. Then, once it's set up, astronomers must constantly tune the system to account for deformation caused by gravity, humidity and other environmental conditions. Liquid mirror telescopes, such as the University of British Columbia's Large Zenith Telescope (LZT), eliminate these problems. The LZT uses liquid mercury as its primary mirror, which can be poured at the site and can maintain a perfect parabolic shape as long as it rotates at a steady speed. It can reflect as much as 75 percent of incoming starlight -- and can do it at about one-fifth the cost of an optical telescope [source: Dorminey].
To date, the LZT holds the record as the largest quicksilver-spinning telescope in the world (it has a 6-meter/20-foot aperture), but India, Belgium and Canada are teaming up to build an even bigger model -- the International Liquid Mirror Telescope, which will do its stargazing from Devasthal Peak in northern India.