Brilliant_ The Evolution of Artificial Light - Jane Brox [118]
Here we have a fine and elegant argument for quieting the doubts of those who, while accepting with tranquil mind the revolutions of the planets about the sun in the Copernican system, are mightily disturbed to have the moon alone revolve around the earth.... But now we have not just one planet rotating about another.... Our own eyes show us four stars which wander around Jupiter as does the moon about the earth, while all together trace out a grand revolution about the sun.
Galileo also observed that the moon Aristotle had perceived as perfect "is not robed in a smooth and polished surface, but is in fact rough and uneven, covered everywhere, just like the earth's surface, with huge prominences, deep valleys, and chasms." As for the Milky Way, he said: "With the aid of the telescope this has been scrutinized so directly and with such ocular certainty that all the disputes which have vexed philosophers through so many ages have been resolved, and we are at last freed from wordy debates about it. The galaxy is, in fact, nothing but a congeries of innumerable stars grouped together in clusters."
In the centuries following Galileo, as telescopes became more powerful and refined, astronomers increasingly saw farther back in space, and farther back in time—to Andromeda, to quasars and black holes—and among the optimum places for observing the stars were the higher elevations of southern California. The nights are generally clear there, and the mountains are not so high that their summits are lost in clouds or snow squalls, yet they rise above the dense atmosphere and fog of the coastal plain. The air is usually calm on the peaks as well: the prevailing onshore winds of the Pacific flow smoothly over them. This stability makes for what astronomers call "good seeing," for it is the movement of air flowing over the earth that distorts the light and causes the stars to twinkle. (By contrast, stars viewed by astronauts in orbit appear steady, while human lights on earth glitter.)
So exceptional was the seeing atop the peaks of southern California that during the first half of the twentieth century, the area became home to some of the most important observatories in the world. The first was the Mount Wilson Observatory, built in 1904 in the San Gabriel Mountains of Los Angeles County. "Many astronomers thought that on a good night the atmosphere over Mount Wilson was so still, the images of the stars so well defined, that it was perhaps the best seeing in the world," wrote historian Ronald Florence. But by the late 1920s, when George Ellery Hale began searching for an appropriate site to situate the 200-inch telescope he was to build, the city of Los Angeles and its suburbs had spread right to the base of Mount Wilson, and urban light was already compromising dark-sky work there. Consequently, Hale decided to house his telescope farther away from the cities, in a fern meadow on Mount Palomar, 5,600 feet above sea level. Palomar was still accessible, yet at forty-five miles from San Diego and one hundred miles from the Los Angeles basin—the 1930 census put the population of San Diego County at about 210,000 and that of Los Angeles and Orange counties at less than 250,000—it seemed safe from the effects of light pollution.
Hale and his backers decided where to situate the telescope in 1930, but it took almost two decades for the lens to be completed—several years alone for it to be successfully cast of Pyrex at the Corning glass factory in New York and another year for it to slowly cool in an annealing oven, after which it journeyed by train across the country, moving at 25 miles per hour during the daylight hours and stopping after dark. Sixteen days after leaving the Corning factory, it arrived in a Pasadena, California, optics lab, where it remained for more than