September 2, 2009In September 2003,
Astronomy magazine published this article about the birthplace of the discovery of the expanding universe. Here is that article, in its entirety. For updates on Mount Wilson Observatory's status, visit Fire threatens Mount Wilson Observatory
Twilight sinks into the jagged mountains, draining color first from the valleys, then from beneath the scrub oak and Coulter pines whose cones sway, fat with sap. Buildings fade from noontime's electric white to hoary gray to black silhouettes against the stars.
Breezes bring air faintly scented of the sea as domes open to the night. On a mountaintop above Los Angeles, distant galaxies and stars have showered light onto the optics of powerful telescopes at the Mount Wilson Observatory for almost 100 years. The observatory is the legacy of one tireless individual, George Ellery Hale, who, while trained in solar physics, found his real calling making American astronomy foremost in the world. Even today, a year from its centennial, Mount Wilson is a testament to his boundless drive and ambition.
Hale (1868-1938) came from a wealthy background and hobnobbed easily with the industrial barons of the Gilded Age. Blessed with energy, organizational ability, and a flair for public relations, Hale swept through astronomy at the turn of the 20th century, when astronomers were changing emphasis from cataloging the positions of celestial objects to understanding how stars worked. Hale realized that as astronomy became astrophysics, it would demand big telescopes with great light-collecting ability.
"Make no small plans," he decided.
In the 1890s, Hale persuaded a streetcar tycoon to build the largest telescope in the world, the 40-inch refractor at Yerkes Observatory in southeastern Wisconsin. Characteristically, even before Yerkes was finished, Hale already was planning his next big project. Through his father's generosity, Hale ordered a 60-inch diameter glass disk for a reflector telescope larger than any in existence. Mirrors, Hale noted, can be supported at the back of the disk, unlike refractor lenses for which the 40-inch was, then and now, the practical limit. Mirror optics thus opened the road to vastly larger telescopes.With astronomy's future in mind, Hale designed the 60-inch telescope for astrophysical research, using photographic plates to capture images rather than an astronomer's eye and sketching hand.
As the 60-inch was being built, Hale convinced the Carnegie Institution of Washington to fund a new observatory in which to house it, support facilities, and several additional telescopes. Wisconsin's Yerkes Observatory suffered from cloudy skies, so he sought a clear-sky site. The solution he found was outstanding — and it's still paying dividends for astronomers. After carefully surveying several locations, Hale selected a wild 5,700-foot-high mountain named Wilson's Peak in the San Gabriel Mountains north of Los Angeles.
Star-test observations proved the astronomical seeing, or image steadiness, was exceptional owing to local geography and meteorology. Observations from the mountaintop are sharp because Wilson's Peak — soon renamed Mount Wilson — is tall enough that it juts above the so-called inversion layer capping the Los Angeles basin. In an "inversion" of the normal dropoff in temperature with height, smooth, tepid marine air rides atop chillier onshore breezes. This gives the lofty observatory spectacular seeing and helps telescopes work at high efficiency.