The Mt. Wilson Telescope Celebrates Its Centennial

Published : Wednesday, November 1, 2017 | 6:08 PM


The Carnegie Observatories is observing the centennial of the Mt. Wilson Telescope, marking the day George Ellery Hale and several other astronomers turned the 100-inch Hooker telescope to peer at the heavens, opening up a whole new way of looking at objects millions of light years away from Earth.

The telescope, named after Hale’s friend John D. Hooker, a businessman who donated $45,000 to the project, is one of two historically important telescopes in the Mt. Wilson Observatory. It was the largest aperture telescope in the world from its completion in 1917 to 1949. Before that, its brother, the 60-inch telescope, was the largest when it was completed in 1908.

Hale conceived and founded the observatory. He had previously built the one-meter telescope at the University of Chicago’s Yerkes Observatory in Wisconsin. The Carnegie Institution of Washington first funded the Mt. Wilson Observatory in 1904, leasing the land from the owners of the Mt. Wilson Hotel.

The observatory is also home to the Snow solar telescope (completed in 1905), the 60-foot solar tower (completed in 1908), the 150-foot solar tower (completed in 1912), and Georgia State University’s CHARA array, which became fully operational in 2004 and was the largest optical interferometer in the world at its completion.

Cindy Hunt, Social Media Strategist for the Carnegie Observatories, said today’s celebration is a momentous occasion that commemorates the day when the telescope “revolutionized our understanding of the universe many times over. In particular, it was the telescope where we found the universe, where Edwin Hubble discovered that the universe was expanding and its science topics that we’re continuing to pursue today.

The astronomer Edwin Hubble, for whom the Hubble space telescope was named, started working with Hale at Mt. Wilson in 1919. Here, on the Hooker telescope, he spent most of his time proving his theory that the universe is expanding and that many objects previously thought to be clouds of dust and gas (“nebulae”) were actually galaxies beyond the Milky Way.
Hunt will appear at a lecture on November 6 at Astronomy on Tap, at Der Wolfskopf Pub in Pasadena, to talk about the history of the Mt. Wilson Observatory and the 100-inch telescope.
“Nobody even knew if a piece of glass that big could be made,” Hunt said. “So George Ellery Hale, who founded the Carnegie Observatories at Mt. Wilson, went to Saint-Gobain glassworks, the place that cast the 60-inch disk. The (100-inch) disk arrived here in Pasadena in December of 1908.”

When it arrived, the mirror wasn’t made to Hale’s expectations; it showed bubbles and other imperfections.
“So (Hale) made them cast more, but the mold kept breaking—they kept having problems. So he went back to that first disk and asked his chief optician to go ahead and grind it down into its curved shape, and it took them six years. From 1910 to 1916, they were grinding that piece of glass into the shape. It was delivered to the mountain on July 1st, 1917 to great fanfare.”
Hunt said people from the area followed the mirror all the way up the mountain, and police had to shut down bridges when the other components of the telescope were hauled up. Finally, first light, the time when the telescope was finally turned on, happened about four months later, on November 1, 1917.


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