17 Tonnes of Spinning Glass: Making the World’s Largest Telescope

This week's guest video comes from Active Galactic Videos: go subscribe! https://www.youtube.com/ActiveGalacticVideos/ They got to walk on the dish of a telescope: https://www.youtube.com/watch?v=1lfXsN45088
At the Richard F. Caris Mirror Lab, under the football stadium of the University of Arizona, there's an enormous rotating furnace, keeping tonnes of glass heated as it forms the mirrors for the Giant Magellan Telescope. Here's a look inside!
I am taking this month off,. and while i'm away,. some other folks are. taking over my channel. we start this week with a couple of. astronomy and physics majors who,. along with professor chris impey. and their team at the university of arizona,. make a channel called. active galactic videos. now the video they've sent is. a little rough around the edges in places. but the idea is so good. that i am genuinely annoyed. that i couldn't go out. and film this myself. so jenny, melissa, over to you. - hi, i'm jenny. - and i'm melissa, and we're here. underneath the university of. arizona's football stadium. in the richard f. caris mirror lab. behind me is the world's. largest spinning furnace. filled with 38,000 pounds of molten glass. - over the next couple of months,. the glass will slowly cool. and start to form a mirror,. one of seven that'll be part of. the giant magellan telescope. once completed, the gmt will. be the largest telescope in the world. the gmt is being built in chile. at the las campanas observatory. in the atacama desert,. and it's scheduled to. see first light in 2022. this massive telescope will have ten times. the resolution of the hubble space telescope,. and more than seven times. the light-gathering power. of the largest telescopes today. the gmt is made of seven. eight-and-a-half-meter mirrors. for a total diameter of 25 meters,. and it will be used to study. galaxies, stars, and exoplanets. - the gmt-5, which is the. mirror being cast right now. is actually the 20th mirror. made at this facility. other mirrors have been. made for other telescopes. like the mmt, the large. synoptic survey telescope,. the twin magellan telescopes,. and the large binocular telescope. it was built under the stadium. to take advantage of the large columns,. which act as load-bearing structures. for all of the heavy equipment needed. it's also nice and quiet when. there aren't football games going on. it's a great way to make football. benefit both the university and science. - to start off, we need. 38,540 pounds of glass. sand is shipped from all over the world. and brought to japan, to. the ohara glass factory. they're the only factory in the world . that can make the e6 low-expansion glass. that's needed for the gmt mirrors. the glass is made in 2,000 pound batches. made exclusively for the. university of arizona. it takes around two and a half years. to make enough glass for a single mirror,. so, you know, plan ahead. - the glass is then. shipped here to tucson. once the mirror lab gets it,. they have to. clean it, inspect it, and weigh it. if there are any stresses or imperfections. in the glass, then the piece is rejected. and made into paperweights. - each individual piece of glass is placed. carefully into the mold and inside the oven. the 40-foot diameter oven. is then gradually heated. to a temperature of. 1,350 degrees fahrenheit. over the course of a week. there are cameras in the. oven to monitor the process. but once it begins,. there's no turning back. at this point, the massive oven. is filled with 19 tonnes of glass. and starts to spin five. revolutions per minute. once the oven reaches. 2,129 degrees fahrenheit,. or 1,165 degrees celsius,. the consistency of the glass. is about the same as honey and. starts to flow into the mold. - and it might make sense. why we need an oven to melt the glass,. but you might be wondering, . "why does it spin ". - it spins to make the shape. we need for a mirror,. a parabola. modern telescopes use parabolic mirrors. to collect and concentrate light. they use the parabolic shape to. get the light into a central focus point,. and the bigger the mirror,. the more light is collected. - but what does have to do with spinning. besides making us dizzy . well, let's take a look. so it turns out that spinning. a liquid actually causes it. to automatically become. this parabolic shape. so whenever you spin the glass,. it creates the perfect. shape needed for a mirror. this is a massive improvement. over how mirrors used to be made. and it "grinds" years off the process. the mirror spends three months. cooling and annealing in the oven. so now it's the right shape. but it isn't quite done yet. when light hits the mirror,. the surface has to be smoother. than a fraction of the. wavelength of light. otherwise the image is distorted. in order to get it this smooth,. the mirror lab spends two. years polishing the glass. it has to be smooth to the point. where no imperfection on the surface. is larger than a virus. after all of that, after melting the glass. in this giant oven, and polishing it for two years,. all you have is a huge,. really smooth piece of glass. - so the mirror lab actually. doesn't make any mirrors. - the final step in turning. this giant piece of glass. into a mirror is actually done. on-site at the observatory. a layer of aluminum. about 100 nanometers thick. is deposited onto the surface. to cover a mirror of this size,. it actually only takes a. soda can's worth of metal. - unlike your mirrors at. home, the reflective coating. is only on the front surface,. so it's very delicate. and needs to be re-aluminized. every so many years. - thank you to everyone here. at the richard f. caris mirror lab. and the steward observatory. tours are open to the public. every day of the week. - go subscribe to active galactic. videos for more like that. i would recommend starting with the video. where they get to walk on. the dish of the telescope. and yes, i am extremely envious. that they got to do that. next week, a language video that you. are probably going to need subtitles for. .
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