Telescopes from the Ground Up

The team cast the Pyrex disk in an entirely new way. Instead of coming up with a solid cylinder of glass, they poured the molten glass into a mold that created a ribbed structure on the back of the disk. The disk was only half as thick as a solid piece of glass and much lighter, but the ribbing kept it strong. And because the glass was so thin, it would adjust to the temperature of the air more quickly, reducing distortions.

Cooling off

The glass was allowed to slowly cool over 10 months, to avoid bubbles and flaws. Then the disk was sent from Corning, N.Y., to its new home at Mount Palomar, Calif. Hale had originally wanted to put the telescope on Mount Wilson, but the area had changed. Light and pollution from the growing city and suburbs of Los Angeles would be terrible for the long exposures needed to photograph distant galaxies. Mount Palomar, the team decided, was a harsh, remote area less likely to attract builders.

The train carrying the glass disk, moving no faster than 25 miles an hour, traveled only by day. It had to take a route that avoided tunnels, bridges, and overpasses because the 17-foot-high case with its precious glass cargo wouldn’t fit in narrow spaces. Curious people gathered to watch the disk’s journey, and the companies involved in making and transporting the disk plastered its case with advertisements to take advantage of the excitement.

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