Mirror casting for new telescope that's 10x sharper than Hubble

With adaptive optics, ground-based telescopes are able to compensate for atmospheric distortions to bring their views of the universe up to par with space-based telescopes like Hubble. An absolutely monstrous new telescope is currently under construction, with a 28-foot mirror starting to be spun just this week.

The telescope that's under construction is called the Giant Magellan Telescope (GMT), and as you've noticed, it's got "giant" right there in the name. It's designed to employ a series of seven 28-foot mirrors, which when arranged together in a honeycomb pattern, will form an optical surface with the equivalent light-gathering capability of a single mirror over 70 feet in diameter.

To make each segment, 21 tons of borosilicate glass are dumped into a mold and then heated to over 2,000 degrees. As the glass melts, the mold spins, causing the molten glass to flow up at the sides and forming a shallow parabola. After this basic shape is established and the glass cools (a process that takes 12 weeks), it'll only take seven more years of polishing to refine the optical surface to the required accuracy, which is about one-thousandth the thickness of a human hair. Once the mirrors are all completed, they'll be mounted together and calibrated to make the final mirror assembly, which should look something like this:


The reason that we can now build all of these awesome telescopes on the ground instead of having to launch them into space is adaptive optics. Using things like lasers to measure the amount of distortion in the atmosphere, modern telescopes can actually flex their mirrors to cancel out all that moving air and render an image at a sharpness that's comparable to space-based telescopes. Since it's way easier (and cheaper) to not have to launch things into orbit, we're able to go big. Very big. And big is where it's at when it comes to telescopes, since the more mirror area you get, the more light you can collect, and the better you can see.

When it's completed in 2018, the GMT should have a staggering four times the light-gathering ability of similar instruments, which means seeing dimmer things in greater detail. It'll be assembled on a mountain in the middle of the Atacama desert in Chile, which (being seriously in the middle of nowhere) is one of the best spots on Earth for stargazing.

GMTO, via New Scientist

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