A Tour of the Largest Ground-Based Telescopes Being Developed Big Glass A Tour of the Largest Ground-Based Telescopes Being Developed

Giant Magellan Telescope (GMT) Las Campanas, Chile First Light 2024

Large Binocular Telescope (LBTO) Mt Graham, AZ, 2007

Large Synoptic Survey Telescope (LSST), Cerro Pachon Ridge, Chile First Light 2022

What do All These New Observatories have in Common? They’re built with BIG GLASS: 8.4 meter primary mirrors

Caris Mirror Lab at U of Arizona Steward Observatory

Building the Giant Mirrors Used in these Telescopes

The Honeycomb structure controls weight and adaptation to temperatures Small-scale casting showing honeycomb structure in relation to thickness of mirrored surface One of 1750 alumina-silica cores used in casting an 8.4 meter mirror The Honeycomb structure controls weight and adaptation to temperatures

Special borosilicate glass is melted in the spin-casting operation

Spin-casting the fourth of seven 8 Spin-casting the fourth of seven 8.4-meter mirrors destined for the Giant Magellan Telescope (GMT). The mold cools slowly for three months after casting to prevent introduction of impurities and imperfections Casting the Mirror

Moving the cast blank in preparation for grinding & polishing

Grinding and Polishing Grinding pedestal is visible in the background; back of mirror is ground flat at this station; front is ground to prepare for polishing. Long bar hanging across the left-center is a laser-measuring device to ensure mirror surface is ground to exacting specifications Grinding and Polishing

Polishing the Aspherical (parabolic) surface The final polishing stage deploys a “stressed-lap” polishing tool that consists of a polishing disk which bends actively to match the varying curvature of the surface The entire mirror surface is polished in stages; here a cleaning assembly is lowered onto the surface Polishing the Aspherical (parabolic) surface

When Complete the Seven Segments will comprise the primary mirror for the GMT, totaling 84.5 ft across

GMT’s Mission and Stats Location: Las Campanas Peak, Chile Elevation 8,500 ft 300 nights / year viewing (minimal rainfall) Purposes: search for exoplanets; study dark matter & dark energy; study formation and fate of galaxies Scheduled first light: 2024

LSST Goals will image the entire visible sky every few nights (thus capturing changes and opening up the time-domain window to the observable universe) Map the interior of the Milky Way—our galactic home in 10 years of observing, the goal is to record the greatest movie ever made billions of objects will be imaged in six colors in an unprecedentedly large volume of our universe

LSST Technical Innovations camera (3200 megapixels, the world’s largest digital camera) each image the equivalent of 40 full moons telescope (simultaneous casting of the primary and tertiary mirrors; two aspherical optical surfaces on one substrate) data management (20-30 terabytes of data nightly, nearly instant alerts issued for objects that change in position or brightness) Public facility—access to images and database for amateur astronomers

What other ELTs are in the works (Extremely Large Telescopes) and how do they differ from these? Thirty Meter Telescope (TMT), Mauna Kea, Hawaii European Extremely Large Telescope (E-ELT), Cerro Amazones, Chile Hint: Like the James Webb Space Telescope, these two telescopes will use large numbers of 1.44 meter hexagonal mirrors in coordinated arrays

Thirty Meter Telescope (TMT) Mauna Kea, HI 2022 (date delayed)

TMT Stats 30-meter diameter 492 optical segments (individual mirrors) Mauna Kea Observatory, Hawaii, 13,290 ft Scheduled First Light 2022 Status: delayed by court order driven by Hawaiian protests

European Extremely Large Telescope (E-ELT) Cerro Amazones, Chile, 2024

E-ELT Stats Overall diameter of primary = 39.3 meters 798 individual hexagonal mirror segments Each segment 1.45 meters across, 50 mm thick Located on Cerro Amazones, Chile, at 10,040 ft. Status: budget approved by European First light scheduled for 2024

Relevant Websites Large Synoptic Survey Telescope Giant Magellan Telescope Observatory (this site has many good links, including more detail about Univ. of Az’s manufacture of 8.4 meter mirrors) Thirty Meter Telescope (site may be down) Large Binocular Telescope Observatory Caris Mirror Lab