3 ms·

The mirror coating timelapse video is pretty awesome https://www.youtube.com/watch?v=Gg9UPS7ndRA https://www.youtube.com/watch?v=Gg9UPS7ndRA

• fastball 1y ago
  Why is the substrate glass? Lack of reactivity? Ability to remove imperfections? As a layman with almost zero knowledge of telescope construction, I feel like a heavy amorphous solid would not be my first choice for the base layer underneath the reflective/mirror coating.
  • minetest2048 1y ago
    Its not your normal soda-lime glass, its more of a glass-ceramic material that have very low coefficient of thermal expansion, something like zerodur: https://en.m.wikipedia.org/wiki/Zerodur https://en.m.wikipedia.org/wiki/Zerodur , which means it can keep its shape and focus even under varying temperature Interesting demo by Huygens Optics: https://youtu.be/qi8jmEbWsxU?si=rj0I3k-l74Xhg7vC https://youtu.be/qi8jmEbWsxU?si=rj0I3k-l74Xhg7vC
    • perihelions 1y ago
      I think while the smaller mirror here is Zerodur, the larger one is just borosilicate, https://astro.arizona.edu/news/rubin-observatory-achieves-another-major-milestone-reflective-coating-84-meter-primarytertiary https://astro.arizona.edu/news/rubin-observatory-achieves-an...
      • IAmBroom 1y ago
        That would be an odd choice. A large glass mirror once cracked because they "only" allowed one year for it to cool. The second one was allotted three years.