Galileo made great discoveries with a telescope fitted with a lens less than 2 inches wide (5 centimeters). However, as astronomers' questions grew to include the fundamental structure of the universe, requiring that they look outside the Milky Way, so did their need for larger telescopes.

Thus, George Ellery Hale envisioned the 200-inch (5-meter) telescope at Palomar Observatory, in northern San Diego County, California. The largest telescope at the time was the 100-inch Hooker Telescope at Mt. Wilson Observatory, also in California and also designed by Hale.

The main feature of the Hale Telescope is, of course, the 200-inch mirror. Hale saw that to make it so big, it would have to weight 20 tons. He also knew that to make the telescope useful, the mirror would have to be made of a stable material that would not expand or contract significantly with temperature. And on mountaintops such as where Palomar is located, the temperature can change dramatically throughout the course of a day.

Hale eventually chose to make the 200-inch mirror out of Pyrex, a particularly heat resistant and stable glass that was a relatively new discovery at the time. Cast in 1934, it required eight months to cool. The mirror was then transported by rail from the glass factory in New York State to the factory in Pasadena, California where it was ground and polished. Twelve years later, because of delays from World War II, the mirror was complete and sent to Palomar. It weighed 14.5 tons.

The designer did not live to see his telescope complete, dying ten years before it was dedicated in his honor in 1948.

Hale also missed the discoveries made by astronomers using the 200-inch telescope, which "opened up the field to understand quasars and the universe of galaxies," says Wallace Tucker, science spokesman for the Chandra X-ray Observatory Center in Cambridge, Massachusetts.

More specifically, scientists verified that quasars are extremely powerful yet distant objects, and that the universe is expanding, as Edwin Hubble theorized.

For 40 years the 200-inch Hale Telescope held the honor of being the largest reflecting telescope. But even today its optics make it one of the world's best observatories and a technological marvel.