In retrospect, Yerkes Observatory optical designer George Ritchey judged the failure of the Melbourne reflector “to have been one of the greatest calamities in the history of instrumental astronomy, for by destroying confidence in the usefulness of great reflecting telescopes it has hindered the development of this type of instrument, so wonderfully efficient in photographic and spectroscopic work, for nearly a third of a century.” Ritchey may have overstated the case, as there were plenty of other design or execution stumbles that reinforced negative perceptions about mirror-based telescopes. Reflector telescopes would indeed grow, nurtured as so often in science by technological innovation. But with the Melbourne debacle, the era of metal mirrors was over.
Even Isaac Newton knew the pitfalls of speculum-metal reflectors, having fabricated several of his own during the late seventeenth century. Much better to endow a lightweight, concaved piece of glass with a reflective surface. Newton deposited tin foil onto glass by immersing them in mercury for several days. But the resulting reflection was best seen through the backside of the glass, reintroducing the light absorption and chromatic aberration a first-surface mirror was supposed to solve. Thin meniscus mirrors and other optical correctives were tried with minimal success over the ensuing decades.
In 1856, driven by an effort to remove caustic mercury from the manufacture of looking-glasses, German organic chemist Justus von Liebig found that a solution of silver nitrate, caustic potash, ammonia, and sugar deposits a reflective silver film onto a glass plate. Shortly afterward, physicist Léon Foucault in Paris and optical designer Carl August von Steinheil in Munich independently applied the method to the creation of silvered-glass telescopes, ranging in aperture from four inches to thirteen inches. To reflector-telescope critics, Foucault cited the distinct visual separation of the close binary star Gamma2 Andromedae in his thirteen-inch instrument.
Frustrated by the haphazardness of grinding glass disks to their proper concavity, Foucault developed his ultrasensitive knife-edge test, in which an illuminating beam reveals a mirror’s surface contours to within a fraction of the wavelength of visible light. Individual bumps could be identified and then polished away until the curvature of the glass was uniform. Astronomical mirrors could now be vetted before leaving the workshop. The pinnacle of Foucault’s telescope-making activity came in 1864 with a thirty-one-and-a-half-inch silvered-glass reflector for the Marseilles Observatory. Work on a government-funded, forty-seven-inch reflector was effectively halted after Foucault’s death in 1868.
Unlike the secretive professional opticians, Foucault published complete reports of his mirror-making methods. In 1857, he addressed the British Association in Dublin on the merits of the silvered-glass reflector. Glass is both lighter and less brittle than speculum metal, and silver is more reflective. Resilvering a glass mirror is trivial compared to the restoration of a speculum disk, which entails a complete regrinding of its curvature. The initial reception to the newfangled technology was tepid: Following an excursion to see Lord Rosse’s speculum-metal Leviathan—a “monstrosity,” in the French scientist’s opinion—Foucault complained to a Parisian colleague, “For the English, mine does not exist.” Nevertheless, how-to articles on silvered-glass reflectors began to appear in English journals in 1859 and quickly leaped the Atlantic to America.
In the ensuing decades, a cadre of optical craftsmen and amateur astronomers stoked the development of silvered-glass telescopes, primarily for their high efficiency and low-cost path to increased aperture. Compared to the sleek, unitized refractor, the contraption-like reflector must have appealed to the astronomical tinkerer, much as a mechanically minded musician might be drawn to the banjo for its array of adjustable elements. In 1867, London optician John Browning published an advertising pamphlet, A Plea for Reflectors, in which he extolled the virtues of silvered-glass instruments. Browning assured his patrons that the days of tarnished metal mirrors were gone: “After some five years’ constant experience in the use of these telescopes, I can assert that nearly all that has to be done, is to carefully let the silver coating alone. Several of my friends have mirrors which have been in use for two or three years, and they are almost unchanged in appearance, quite so in performance.”
Given the cheapness of the glass and the relative ease of fabrication, reflectors enjoyed a huge cost advantage over refractors (and still do). A Browning ten-inch reflector, complete with equatorial mount and clock drive, could be had for about £200, a fraction of the price of the same-size achromatic refractor. And whereas Lick Observatory paid $50,000 just for the objective lens of its thirty-six-inch refractor, its thirty-six-inch Brashear reflector came in at half the amount—including the dome, mount, and spectrograph.
John Browning’s contemporary George Calver likewise launched production of silvered-glass reflectors. Most notable was Calver’s thirty-six-inch telescope, with which Andrew Common produced his breakthrough 1883 photograph of the Orion Nebula and James Keeler his revelatory plates of spiral nebulae. The 1870s saw Henry Draper’s parallel endeavor to advance large-aperture reflectors in the United States. The ability of Draper’s twenty-eight-inch telescope to record the first stellar spectrum in 1872 suggested the reflector as a viable research instrument. Still there was considerable pushback from the astronomical community. Oxford University astronomer Herbert Hall Turner spoke for many when he commented that the “reflector is so seriously influenced at times by air currents and changes of temperature as to be an instrument of moods and Dr. Common has accordingly compared it, somewhat ungallantly, to the female sex.”
The reflector-versus-refractor debate continued into the 1890s with now some dozen lens-based telescopes exceeding two feet in aperture. Having completed the largest-in-the-world Yerkes refractor, Massachusetts optician Alvin Graham Clark boasted to George Hale about the feasibility of a seventy-two-inch lens. Hale dismissed the idea. Such a behemoth would be impossibly long and its thick glass matrix would severely winnow precious cosmic photons. For the astrophysicist seeking to photograph a spectrum, the refractor’s chromatic aberration was especially problematic. “No combination of lenses yet devised,” Hale advised his colleagues, “can compare with a paraboloidal mirror in the capacity to unite in a single focal plane all wave-lengths.”
The Yerkes forty-inch, George Hale rightly suspected, marked the historical zenith in the aperture of refractor telescopes. If astronomers were to probe farther and fainter, they had no choice except to muster the resources to enlarge mirror-based instruments. Yet these next-generation reflectors could share none of the quirky, ad hoc construction of their predecessors; they would have to equal—indeed, surpass—the level of refinement long associated with their refracting counterparts.
While his sixty-inch mirror-blank lay fallow in the Yerkes basement, lacking funds for completion, Hale turned his attention to a more modest instrument only recent installed under the southeast dome. George Ritchey’s twenty-four-inch reflector was an engineering masterpiece, the product of five years of labor by an unapologetic perfectionist. The low-slung mount, fabricated in the Yerkes workshop where Ritchey reigned, was designed to shoulder its burden with stoic mechanical aplomb. Its internal clock drive was accurate enough that a star centered in a high-power eyepiece drifted less than a hundredth of a millimeter over four hours. The tube—a cylindrical octet of steel bars bonded to cast-aluminum rings—was judged so rigid that the planned supplementary bracing was scrapped. The mirror had been painstakingly hollowed to a deep curvature, converging light far more efficiently than a conventional long-focus instrument. In an hour’s exposure, Ritchey’s reflector recorded stars beyond the reach of the renowned forty-inch refractor down the hall.
George Ritchey.
In a 1901 report, which included an arresting photograph of the Andromeda Nebula, Ritchey affirmed that his telescope was a test-bed for the future sixty-inch. The lessons learned would be applied to its eventual design and construction, virtually assuring its success. This was a telescope that
needed to be built. And if the point was missed, Ritchey’s paper included handsome cross-sections of the sixty-inch reflector, fully mounted and pointed skyward, under an expansive dome.
Although eager to progress, both Hale and Ritchey were aware that their envisioned leap in telescopic aperture and sophistication might be nullified by the mercurial climate of the Great Lakes region. When they looked upward from Williams Bay, Wisconsin, even on the crispest nights, their mind’s eye saw a turbulent gauntlet of air that contorted light rays en route to the ground. The windswept outskirts of Chicago was not the proper site for a megatelescope. “It would be interesting to think of the photographic results which could be obtained with a properly mounted great reflector in such a climate and in such atmospheric conditions as prevail in easily accessible parts of our own country,” Ritchey mused, then added, “notably in California.”
Chapter 25
THREADS TO A WEB
The stars looked like jewels on black velvet. The sky was rich and dark, and every star was a glowing, living point of light.
—George Ellery Hale at the summit of Mount Wilson, 1912
THURSDAY MORNING, JUNE 25, 1903, found George Hale on the back of a burro ascending the fogbound flank of Mount Wilson, surely the most erudite burden ever borne by the ragged beast. On a second burro rode Lick Observatory’s William Campbell, who reassured the pessimistic Chicagoan that altitude would carry them above the mists that collared the hills outside Pasadena. Hale was unconvinced. The landscape was veiled in white, and a glance overhead revealed only a diffuse notion of the Sun’s presence.
The two-foot-wide trail had been given the wishful designation “Mount Wilson Toll Road” long before its expansion merited the name. Hale was here only nominally on behalf of the Carnegie Institution, which had commissioned him, Campbell, and Lick’s William Hussey to seek favorable sites in southern California for a new solar observatory. In truth, Hale had traveled west for his own interests. The climatic environment of the Yerkes Observatory oppressed him. A cloudless Lakes-region sky that, to the untrained eye, looked perfectly transparent, Hale saw as an enervating soup of air molecules that drowned cosmic photons before they reached the telescope. For all its fame, the forty-inch refractor was hobbled by its placement outside Chicago. Since its inception, Hale had pictured the instrument atop a mountain, like its kin at Lick Observatory. And what of his sixty-inch reflector, lying fallow, a mighty eye lacking a body? If provision ever arrived for its completion, what sense did it make to erect such a responsive telescope under the attenuated rays of a growing metropolis?
Hale had learned of Mount Wilson’s pellucid skies as a college student in 1889, when a scouting team from Harvard pronounced the mile-high perch the best astronomical observing site in the nation. (However, they cautioned against the rattlesnakes.) Mount Wilson, Hale had been told, was cloudless some three-hundred days a year, and the fog that blanketed the valley rarely crept to the summit. Even the warm Pacific breeze tuckered itself out before reaching the mountain, leaving the air at the peak clear and steady. Now, fourteen years later, on the back of a burro, Hale was about to enter a world astronomers spoke of with almost mystical awe.
As Hale’s animal plodded up a ridge, there was a perceptible brightening. Then, as though a curtain had been thrown aside, the fog evaporated to reveal a breathtaking vista. Mountain ranges stood in sharp relief against a cerulean sky. Along their slopes, a primitive landscape of rocky outcrops, canyons, trees, and thickets. Westward in the distance, the Pacific and, at the horizon, the silvery band of Catalina Island. Hale and Campbell arrived at the summit during the afternoon and joined Hussey that evening to view the heavens with a telescope. As the Harvard expedition had long ago concluded, the gain in altitude and the absolute clarity of the air rendered stars as brilliant specks.
Hale rose early to catch the sunrise, then scouted the rolling highland of pine stands and grassy meadows. At intervals, he climbed a tree to assess solar observing conditions above the ground; one notebook entry has him shimmying sixty-eight feet skyward on a yellow pine. Freshwater springs spewed a sufficient amount of water for a sizable community of workers. With each turn of the trail, each scrub-covered flat, each bulging outcrop, the institute of his dreams grew clearer: a solar telescope, the sixty-inch reflector, workshops, offices, lodgings—all appeared through his mind’s eye in their proper places. One top-of-the-world promontory Hale dubbed Monastery Point, after the holy houses of the Levant. Here he envisioned a stone-walled aerie for himself and his fellow acolytes of astrophysics.
The prospect of a mountaintop observatory had long captivated George Hale, but a recent development raised his simmering hopes to a fever pitch. On January 13, 1902, Hale opened the Chicago Tribune to find that Andrew Carnegie had donated ten million dollars to establish a research institute of unprecedented magnitude and breadth. The organization’s mandate, in the words of the reporter, was to “discover the exceptional man in every department of study . . . and enable him, by financial aid, to make the work for which he seemed especially designed his life-work.” Hale had no doubt that he was such a man.
Eleven days later, Hale sent the Carnegie Institution a proposal for creation of a comprehensive astrophysical research center on Mount Wilson, including a solar observatory and a facility for the sixty-inch telescope. Estimated startup cost: $300,000—with additional outlays to come. To buttress his ambitious plan, Hale included a photograph of the Orion Nebula taken by George Ritchey with the Yerkes twenty-four-inch reflector. If a telescope two feet in aperture, on the lowlands outside Chicago, can generate such an exquisite image, imagine what a five-foot instrument might do, elevated above the hazy underlayment of the atmosphere.
Hale’s frontal assault on the Carnegie Institution’s treasure was firmly repulsed by its executive board, who weighed proposals from eighteen fields of study running the gamut from geophysics to nutrition. Not only was he up against luminaries in these other branches of science, but also traditional-astronomy strongmen like Simon Newcomb and Lewis Boss. Even his nominal ally, Edward Pickering, found the plan extravagant. The Carnegie Institution questioned the wisdom of granting such a massive infusion to a single project, especially in a field—astrophysics—that its veteran advisors characterized as yet embryonic. Instead, it commissioned Hale, Campbell, and Hussey to seek favorable sites in southern California for a new solar observatory.
Standing on Mount Wilson in June 1903, Hale knew that he had found the home for his astrophysical research center. His technical report to the Carnegie Institution executives painted as clear a picture of its crystal skies as one could without resorting to poetry. But he was not about to wait for their judgment or their money. “I am a born adventurer,” he once confessed, “with a roving disposition that constantly urges me toward new long chances.”
Six months later, Hale moved with his family into a rented bungalow in Pasadena, eight miles from the base of Mount Wilson. The nominal aim of his so-called Yerkes Expedition was a more thorough assessment of the summit’s solar-observing potential. In truth, Hale pooled his family savings with loans from his brother and his uncle and began construction of his mountaintop observatory.
Among the first to hitch his star to Hale’s was former Yerkes graduate student, now staff astronomer, Walter S. Adams. Brilliant and convivial, Adams had completed his doctoral studies at Munich to great acclaim. “The prospects of a bohemian year on Mt. Wilson with you appeal to me very strongly indeed,” Adams confessed, “and I should be only too glad to join you for what would cover ‘Omar’s loaf of bread and jug of wine.’” Hale paid Adams out of his own pocket. With a small grant from the Carnegie Institution, he also supported Ferdinand Ellerman, his longtime photographic assistant, and George Ritchey, the gifted optical designer and guardian of the sixty-inch mirror. Ellerman embraced the rough life, donning a ten-gallon hat, high boots, and a cartridge belt with a loaded revolver and a hunting knife. The sight of his heavily armed friend startled Adams, who envi
sioned “a struggle for existence on the wild mountain top.” Visiting astronomers were welcomed: A trainee from Padua recalled hiking the trail to the summit while Hale recited verses from the Divine Comedy in fluent Italian.
Walter S. Adams.
Adams’s recollections of the observatory’s formative days convey the spirit of adventure felt by Hale and his staff. They were pioneers of astrophysical science, drawn to far-off geography to gain best vantage on the luminous rustlings of the cosmos. At the time, Pasadena was barely two decades old, a rail-nurtured city of twenty-five thousand, with grand hotels, architect-designed mansions, and East Coast aspirations. The citified core dwindled rapidly toward its outskirts, giving way to dirt roads, bungalows, and farm fields.
Hale made frequent trips up the mountain, bicycling to its base and overnighting at a ramshackle cabin near its summit, where he watched the diurnal roll of the night sky through a hole in the roof. With local hands and muled-in supplies, he restored the cabin, installing a granite-block fireplace in anticipation of winter. A minilibrary of astrophysics and poetry books capped off the renovation. On the steep-sided promontory Hale had charted a year earlier, workers completed construction of his astronomers’ lodge: the Monastery.
Starlight Detectives Page 33
