200-inch Disk

This 20-ton, 200-inch (5-meter) disk is one of the world's largest pieces of cast glass. It was to serve as the gigantic mirror for what later became known as the Hale telescope, but the casting mold broke, ruining the disk, and a second casting had to be made. Some astronomers thought the universe was one grand galaxy. Others thought it contained many. In 1906, astronomer George Hale set out to build a telescope that could gather enough light to settle the debate. Hale had already built the world's biggest reflecting telescope. Its 60-inch (1.5-meter) mirror was made from the largest piece of glass that had ever been cast. Still, it wasn't big enough. Making a larger one would be difficult, but that didn't stop Hale. After four painful years of pushing glassmakers to their limit, he had a mirror blank nearly double in size. When astronomer Edwin Hubble used Hale's new 100-inch (2.5-meter) telescope to study the heavens, the debate was settled. Our galaxy is just one among many. Hale still wasn't satisfied. He wanted a 200-inch (5-meter) reflector. Would it be possible to make such an enormous mirror blank? In 1934, under the direction of physicist George McCauley, Corning Glass Works succeeded - on the second try. The new Palomar Observatory's giant Hale telescope stretched the boundaries of our knowledge, revealing an astounding universe made up of billions of galaxies.