From the Archives: Work resumes on Palomar Observatory’s 200-inch mirror

A few months after the end of World War II, on Dec. 3, 1945, workers at the Caltech Optical Shop resumed grinding work on the mirror of a 200-inch Palomar Observatory telescope.

Work had been halted in 1942 when engineers, scientists and Caltech laboratories were assigned war-related work.

A short story in the next day’s Los Angeles Times reported:

Work was resumed yesterday afternoon on California Institute of Technology’s 200-inch telescope mirror which had been untouched since 1942 when it was covered with canvas on the huge grinding machine in the Caltech Optical Shop.

As the Big Eye revolved again on the grinding table, Dr. John A. Anderson, who has directly supervised work on the Palomar Observatory project since 1928, and Marcus H. Brown, chief optician and head of the optical shop, were all smiles.

“We hope that within 18 months the mirror will have been installed in the now virtually completed observatory on Palomar Mountain in San Diego County,” Dr. Anderson asserted.

Since actual work on the mirror was started in 1936, some four and a half tons of glass have been removed in shaping the huge reflector. It now weighs about 15 tons. The grueling job of grinding the mirror’s face into a concave form which, if extended, would constitute the inner surface of a perfectly round ball, has been successful. The work resumed yesterday will continue the task of changing the face from a perfectly spherical surface to a parabolic form that, unlike the sphere, will focus the faint light trapped from stars situated at the fringes of the universe. The parabolizing requires the deepening of the central part of the mirror by a few thousandths of an inch.

The mirror was transported to Palomar Observatory in 1947. The 200-inch telescope was dedicated in 1948.

This post was originally published on March 15, 2012.

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