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By Root 994 0

a decade as technicians, working with slurries of abrasives and with polishing rouge, ground away ten thousand pounds of glass and shaped the lens into a paraboloid. Meanwhile, crews improved the road to the summit of Mount Palomar, ran water and electric lines up the mountain, and built a dome to house the telescope. The Japanese attack on Pearl Harbor in 1941 put a stop to all work there, while almost everyone involved with the project was taken up by the war. The lens was finally trucked up the mountain in 1947. Although the population of southern California had grown markedly and New Deal electrification initiatives had increased the amount of light in homes and on the streets, Palomar remained a remote mountain rising out of the desert. Cattle grazed in the high meadows, and no appreciable light affected the observatory.

The Hale Telescope saw first light in January 1949, and on that occasion the eminent astronomer Edwin Hubble claimed: "The 200-inch [telescope] opens to exploration a volume of space about eight times greater than that previously accessible for study.... The region of space that we can now observe is so substantial that it may be a fair sample of the universe as a whole." After months more of adjustments—opticians polished the last five- or six-millionths of an inch of the lens with hand-held cork tools and then their own thumbs—the telescope was officially turned over for exploration and research. Astronomers identified stars and studied their birth, evolution, and death; studied the workings of the galaxies; and searched for the age of the universe itself. "Astronomy is an incremental science," Florence wrote. "Each night adds data, fragmentary glimpses and measurements of the reaches of the universe.... Amidst that steady accumulation of knowledge, the achievements of the [Hale] telescope stand out as a history of twentieth-century astronomy."

But by the 1960s, light pollution began to compromise the quality of dark-sky study at Palomar—as it has at many observatories throughout the world in the past fifty years. In some places where dark-sky study is severely limited or impossible, institutions such as the David Dunlap Observatory outside Toronto and the Yerkes Observatory outside Chicago have been transformed into historical sites and education centers. Even in working observatories, quite a few celestial objects simply aren't apparent anymore. "It's like I'm looking for the glitter of a little pen-ray flashlight in the glare of bright sunlight," commented one astronomer at the Kitt Peak National Observatory outside Tucson, Arizona. "That 20 percent increase in sky brightness means it takes us 40 percent longer to record the same faint, distant objects. You get less done per expensive hour of operating the telescope."

Sometimes there isn't enough dark time in a night to record an object at all anymore. In addition, mercury vapor lamps—the most popular type of street lighting—do more than blot out the stars. They also compromise astronomers' ability to take an object's spectra—that is, split the light from the telescope into its component colors. Astronomer Dave Kornreich explains:

When you take a spectrum of fluorescing objects like galaxies, you see that the spectrum is not smooth, but made up of a number of lines. Each line is a unique indicator of the presence of a certain chemical. By studying the strengths of these lines, astronomers can deduce the chemical composition and temperature of the objects they observe.... Mercury vapor lamps have an enormous number of these spectral lines in all parts of the spectrum [which] interfere with astronomical observations.

By 1980, when the population of San Diego County had grown to just under 2 million, light pollution around Palomar had become so severe that in the following years, scientists at the observatory, in an effort to counter the further increase of pollution, began working with the surrounding town and county governments to try to reduce unnecessary lighting and glare in the area. Light pollution may appear to be as complex as modern