Largest single-piece, stiff telescope mirror ready for cleaning

Specialists at the University of Arizona Steward Observatory Mirror Laboratory (Tucson, AZ) have lifted the first 8.4-m-diameter borosilicate honeycomb mirror from its furnace hearth to a position where its 1662 ceramic cores can be removed. The cores were used to form the hollow glass honeycombs that make the mirror stiff and light and allow it to be quickly cooled to nighttime air temperatures. When the mirror is cleaned, it will weigh approximately 21 tons, down from the 45 tons at the time o

Apr 1st, 1998

Largest single-piece, stiff telescope mirror ready for cleaning

Specialists at the University of Arizona Steward Observatory Mirror Laboratory (Tucson, AZ) have lifted the first 8.4-m-diameter borosilicate honeycomb mirror from its furnace hearth to a position where its 1662 ceramic cores can be removed. The cores were used to form the hollow glass honeycombs that make the mirror stiff and light and allow it to be quickly cooled to nighttime air temperatures. When the mirror is cleaned, it will weigh approximately 21 tons, down from the 45 tons at the time of lift.

The mirror was spin-cast in January 1997. In May 1997 an extra two tons of glass were added to thicken part of the faceplate, and the surface was remelted. Grinding and polishing of the mirror will begin this fall. This mirror is the first of two to be installed at the Large Binocular Telescope (LBT) under construction on Mount Graham, AZ. The LBT will see faint objects with more detail than any other ground- or spacebased telescope. Partners in the LBT are the University of Arizona, Arcetri Astrophysical Observatory (Florence, Italy), a consortium of German astronomical research institutions, Research Corp. (Tucson, AZ), and The Ohio State University (Columbus, OH).

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