Palomar Mirror

StarDate: December 2, 2009

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During the Great Depression, people had to find entertainment wherever they could. One spot was at the Corning Glass works in New York. The company was casting the mirror for the 200-inch telescope at Palomar Mountain, California. People were so enamored of this "Giant Eye" that they bought tickets to watch the mirror being cast.

That process began 75 years ago today, when workers at Corning Glass began melting 20 tons of glass.

It was a daunting task. Large telescope mirrors can sag under their own weight. And glass expands and contracts as it heats and cools. Both of these things can ruin the view of the night sky.

So after several failed attempts with conventional glass, Palomar Observatory turned to Corning and its new material, Pyrex -- the same type of glass used in cookware. It doesn't expand and contract very much, making it a perfect material for telescopes.

The first casting failed. But a second -- which started on December 2nd, 1934 -- was a success. After months of work, the mirror was shipped cross-country by train in 1937 -- another public spectacle. And after World War II, technicians finished grinding its curved surface to within a few millionths of an inch of the proper shape.

The 200-inch telescope was dedicated in 1948, and was the largest telescope in the world for three decades. Today, it remains an astronomical workhorse -- a "Giant Eye" that's still looking into the night sky.

Script by Damond Benningfield, Copyright 2009

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