Fifth mirror for Giant Magellan Telescope has been cast

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The fifth mirror, out of seven, for Giant Magellan Telescope (GMT) has been cast by the University of Arizona mirror lab.

With its casting this weekend, the fifth GMT mirror joins three additional GMT mirrors at various stages of production in the Mirror Lab. Polishing of mirror 2’s front surface is well underway; coarse grinding will begin on the front of the third mirror shortly and mirror number 4, the central mirror, will soon be ready for coarse grinding following mirror 3. The first GMT mirror was completed several years ago and was moved to a storage location in Tucson this September, awaiting the next stage of its journey to Chile. The glass for mirror 6 has been delivered to Tucson and mirror seven’s glass is on order from the Ohara factory in Japan.

In time, the giant mirrors will be transported to GMT’s future home in the Chilean Andes at the Carnegie Institution for Science’s Las Campanas Observatory. This site is known for being one of the best astronomical sites on the planet with its clear, dark skies and stable airflow producing exceptionally sharp images. GMTO has broken ground in Chile and has developed the infrastructure on the site needed to support construction activities.

If all goes right, GMT will begin its science work using 4 mirrors in 2020, with the use of all 7 mirrors beginning in 2022. This will be several years before the larger Thirty Meter Telescope and the European Extremely Large Telescope.



  • wayne

    Cool development.

    Have a sampling of Sky & Telescope magazines from the mid 60’s; The University of Arizona comes up quite a bit, referencing the casting of large mirrors. (their spinning-oven apparatus, is quite impressive.)
    Back then, “Cer-vit” Brand glass from Owens Corning was the new-thing. (1967-1978)

    Am I right to assume the U of A is one of the top places for the casting of telescope mirror’s?

  • Joe

    Note to self, go to Chile to see night time sky!

  • Wayne: The UofA mirror lab is the world’s premier place for casting large telescope mirrors. In fact, no one else does it. You should read my March 2014 S&T article on GMT and the mirror lab.

  • wayne

    Cool. I will follow up. (That’s what I thought, ref U of A.)

    (again, the spinning oven, is very cool)
    UA Mirror Lab Casts Third Mirror for GMT

  • Dick Eagleson

    The UofA Mirror Lab is certainly impressive. But there’s a German company named – amusingly – Schott Glass that has its own proprietary near-zero-expansion glass formulation called Zerodur®. The company has been involved in several large-format astronomy projects including the European Extremely Large Telescope. I don’t know if Schott has the capability of casting monolithic mirrors of 8.4 meters diameter, but they’re definitely a player. Schott Glass seems to be pretty much the Corning of Germany.

  • wayne

    Great historical stuff! You encouraged me doing some mini-research.

    Never looked up “Cervit” before, but I see it’s related to Zerodur and a Russian brand, Sitall.

    I see that Otto Schott developed Borosilicate glass, (‘Duran’ brand) in 1893, 22 years before Corning developed Pyrex brand. And if Wikipedia is to be believed, “Pyrex made its public debut in 1915 during World War I, positioned as an American-produced alternative to Duran.”)

    Back to the GMT–made from “E6 glass” from the Ohara Corporation of Japan.

  • Dick Eagleson

    So Pyrex was the “Victory Cabbage” (sauerkraut) of glassmaking, eh? Interesting to know.

    I seem to remember reading that UofA uses a type of borosilicate glass to make its mirrors. Maybe “E6” falls into that category.

    And who knew the Irish were so big in Japan? :-)

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