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Corning, PYREX® and Telescopes

Hale Telescope          
Figure 1. The Hale telescope shown here was the world's largest telescope for almost 45 years until 1993 when the Subaru telescope, whose mirror blank was also made by Corning, was launched (Photo courtesy of Caltech).   

Corning's history of providing technology for astronomical applications dates back to 1935, when Corning produced the 200-inch mirror blank from PYREX® glass for the Hale telescope on Mount Palomar. Since then, Corning has set the standard for fabrication of lightweight mirrors for space applications. Our expertise in mirror blank fabrication has enabled many of the world's most powerful telescopes, including the Hubble, Subaru, and Discovery Channel telescopes.


     Mirror Blank
  Figure 2. Two Corning employees standing on the cooled mirror blank at the factory (Photo courtesy of Caltech).
   Honeycomb Structure of Mirror Blank
  Figure 3. The honeycomb structure greatly reduced the weight of the giant mirror blank but it still weighed over 20 tons (Photo courtesy of Caltech). 
   PYREX Telescope Disc 
  Figure 4. It took 14 days at 25 miles per hour top speed to ship the 200 inch mirror blank to California (Photo courtesy of Caltech).

The 200-inch (508 cm) diameter Mt. Palomar telescope project was started in 1929 and funded by a six-million dollar grant from the Rockefeller Foundation. It was led by astronomer George Hale who realized from his work with the 100-inch diameter Mt. Wilson telescope that such a large mirror needed to be made from a very low expansion material to be useful. Initially he worked with the engineers at General Electric who tried to fabricate it from fused quartz without success. In 1932 he turned to Corning whose scientists felt that their PYREX low expansion borosilicate glass used for laboratory glassware could meet his requirements.

Corning scientists first successfully created several smaller discs to develop the technology and test different glass formulations. They then cast two 40,000 pound discs; the first had flaws but was used as an experimental test bed to insure the success of the second disc which, after slowly cooling for almost a year, was finished in 1935 . The first unfinished disc is now part of the Corning Museum of Glass (Figures 2 and 3).

The second disc was sent across the country by rail to be polished at the Caltech optics lab in California (Figure 4). Careful and laborious polishing removed 10,000 pounds of glass from the disc and was not completed until 1947 as a result of work being stopped during World War II.

Astronomer Edwin Hubble took the first pictures through the telescope in 1949. It is named after its creator – George Hale – who died in 1938 without seeing his project completed. The Hale telescope was the world's largest telescope for almost 45 years until 1993 when the Subaru telescope, whose mirror was also made by Corning, was launched.  To learn more about the history of the amazing Hale telescope from the astronomy web site at Caltech, please click here .

The Subaru telescope now features the world's largest primary mirror (over 2100 inches or 8.3 meters in diameter) and was made of Ultra Low Expansion fused titanium glass manufactured by Corning. With this mirror, the Subaru telescope is capable of capturing detailed photographs of galaxies 13 billion light years away.