By Emily Levesque, University of Washington
George Ellery Hale was born in 1868. He built his first telescope when he was 14. At the age of 24, Hale was a professor at the University of Chicago. He founded the Yerkes Observatory and began a lifelong career of building big telescopes, breaking his own records to ultimately build the largest telescope in the world four times.
The Largest Telescope Needs the Largest Lens
In 1904, George Ellery Hale moved to California and founded the Mount Wilson Observatory near Pasadena. He began by building a telescope with a 60-inch primary mirror for the observatory, which was enormous at the time, but before the telescope was even complete, he had started on a new record-breaking project.
This new telescope was to have a primary mirror of 100 inches diameter. Fashioning mirrors of this size was an immense undertaking. The mirror would have to have very few, if any, imperfections. From the beginning, the disk was plagued with problems: it was 101 inches across, 13 inches thick at the edge, and weighed four and a half tons; it was the largest piece of plate glass ever cast.
Unfortunately, the glass also arrived filled with sheets of bubbles, formed between the several layers that had been poured to make up the disk. Hale and his colleagues assumed the bubbles had rendered the glass useless, too weak to hold a surface shape or stay structural in a telescope, and ordered a new disk.
Back to Square One
The problems continued. A second disk was poured in France in 1910 but broke while it was cooling; a third also broke a year later, and a fourth was successfully poured with a thinner shape but seemed unlikely to stay intact inside a telescope.
Eventually, Hale and the observatory’s assistant director, Walter Adams, had another look at the original bubble-filled disk along with glass expert Arthur Day. Day declared that the bubbles might not be a problem.
Hale and Adams oversaw the painstaking grinding down of the disk into a parabola-shaped surface, called a mirror blank; a process that took five years and included delays due to World War I.
This article comes directly from content in the video series Great Heroes and Discoveries of Astronomy. Watch it now, on Wondrium.
George Hale’s First Record
Fortunately, by 1916, the shaping of the glass blank for the mirror was complete, ground down to only 9,000 pounds. The final step was to apply a reflective layer of silver to the curved glass surface of the blank, finally transforming it into a mirror. The mirror was then driven from the Pasadena lab to the summit of Mount Wilson via truck, an eight-hour trip with the truck driving just one mile an hour the whole way.
Upon its successful first light in 1917—the term used for the first time a telescope is turned on and captures an image from the night sky—Hooker’s 100-inch telescope did indeed become the largest telescope in the world. The 100-inch telescope went on to make some of the most groundbreaking discoveries in all of astronomy, literally reshaping humanity’s picture of the universe.
Bigger Is Better
It took just 10 years for Hale to start working on breaking his own record again. His new goal was a 200-inch telescope, the next step in his ongoing dream to create the world’s largest telescopes.
Two hundred inches may not sound that large, but it translates to a diameter of more than 16 feet. After all of the trials and tribulations with the Hooker telescope mirror at Mount Wilson, building a gargantuan 200-inch mirror was an immense undertaking. However, Hale and his colleagues had learned a few lessons since their experience with the bubbly mirror disk that was in use at the 100-inch.
During that telescope’s original first light, Hale had been mortified to look through the telescope and see a messy hodge-podge of duplicate images rather than a single clear picture. They later learned that the mirror had been left exposed to the sun earlier that day, which heated and temporarily deformed the glass.
Once the mirror cooled, the image was perfect, but Hale was still eager to find a medium for the mirror blank that would be less susceptible to heat. Hale approached Corning Glass Works in New York to cast the 200-inch mirror disk out of a new glass blend famous for its robustness when faced with extreme temperatures: Pyrex. Corning agreed to cast the mirror. It took a month just to melt the glass needed for the disk!
Breaking Another Record
The mirror disk traveled by railroad for over two weeks to make the journey from New York to Pasadena and the optical shop at the California Institute of Technology. After arriving at Caltech, the mirror disk then spent a total of 11.5 years in the optical shop, including delays during World War II and the painstaking process of being ground from a 20-ton disk into a 14.5-ton parabolic blank.
Finally, the mirror was installed at the telescope atop Palomar Observatory. The official first-light photos from the 200-inch were taken in January of 1949 by astronomer Edwin Hubble. The 200-inch telescope would later go on to make record-breaking discoveries on the size of the universe, the chemistry and evolution of stars, and the physics of distant supermassive black holes.
Unfortunately, George Ellery Hale didn’t live to see the completion of his final, largest telescope; he died in February of 1938, a full decade before the 200-inch saw first light. His New York Times obituary suggested that the new 200-inch be dedicated to him, and at the telescope’s dedication, it was officially named the Hale Telescope.
Common Questions about George Hale, the Maker of Massive Telescopes
The glass had been filled with sheets of bubbles, formed between the several layers that had been poured to make up the disk. George Hale and his colleagues assumed the bubbles had rendered the glass useless, too weak to hold a surface shape or stay structural in a telescope.
Hale had wanted to use a medium for the mirror blank that would be less susceptible to heat. So Pyrex was used as it was a new glass blend famous for its robustness when faced with extreme temperatures.
George Hale didn’t live long enough to see the completion of the telescope that broke the record for being the largest telescope in the world. So the telescope was named after him to remember his legacy.
