Starlight Detectives

by Alan Hirshfeld

  George Ellery Hale.

  Reading of the nascent science that would become astrophysics, Hale was intrigued by Janssen’s and Lockyer’s independent discovery in 1868 that the emission spectrum of solar prominences is bright enough to be seen outside of eclipse. Princeton’s Charles A. Young subsequently found that if the spectroscope is centered on a particular emission line (say, the red alpha-line of hydrogen) and the spectroscope slit is widened, a single-color image of the prominence presents itself to the eye. In Young’s popular book, The Sun, Hale drank in the stirring description of the sight:

  The red portion of the spectrum will stretch athwart the field of view like a scarlet ribbon, with a darkish band across it, and in that band will appear the prominences, like scarlet clouds—so like our own terrestrial clouds, indeed, in form and texture, that the resemblance is quite startling: one might almost think he was looking out through a partly opened door upon a sunset sky, except that there is no variety or contrast of color; all the cloudlets are of the same pure scarlet hue.

  Young goes on to detail the technical facets of solar observation, then concludes in a coda that aroused Hale’s curiosity:

  Setting the spectroscope upon this latter line [in the violet part of the spectrum] and attaching a small camera to the eye-piece, it is even possible to photograph a bright protuberance; but the light is so feeble, the image so small, the time of exposure needed so long, and the requisite accuracy of motion in the clock-work which drives the telescope so difficult of attainment, that thus far no pictures of any real value have been obtained in this manner.

  Indeed, if the eye can so plainly see these solar outbursts outside of eclipse, why cannot the camera? The multiple impediments cited by Young—faintness, smallness, photographic insensitivity, and mechanical imprecision—were together a veritable siren song to Hale. Here was a complex challenge in astrophysical observation, one that required thoughtful, persistent, yet flexible attack.

  In July 1889, Hale found himself riding the cable car along Chicago’s Cottage Grove Avenue. As the coach rumbled along, he caught sight of a white picket fence lining the side of the road. The pickets reminded him of lines in a spectrum, the car’s forward movement causing his fixed eye to scan across the lattice of vertical strips. In that instant, Hale envisioned the spectroscopic innovation that would permit the photography of solar prominences.

  Hale’s “spectroheliograph” would have two slits instead of the usual one. The entry slit would transmit a thin slice of the Sun’s image-disk, as one might crop a portrait to depict only the nose and the features above and below it. The exit slit, situated after the light’s blended colors have been dispersed by the grating, would isolate from the spectrum a solitary wavelength, which in turn strikes a photographic plate behind the slit. Were the two slits to remain stationary while the telescope tracked the Sun, the resultant picture would be a monochromatic rendering of the original slice of the solar disk. But were the slits moved in synchrony at the proper rate, a one-color scan of the Sun’s surface is created.

  Point the device at a prominence on the Sun’s limb, and the slits’ harmonized movement effectively creates a picture of the outburst: The height of the targeted spectral line lengthens and shrinks with the prominence’s contours, while the line is simultaneously shifted to unexposed areas of the plate. (The same might be accomplished with stationary slits and a moving plate.) The width of each slit must be properly adjusted: too narrow and there is insufficient light to form the image, too wide and the ambient solar light fogs the plate.

  In November 1889, Hale received permission from Edward Pickering to try his spectroheliograph on Harvard’s fifteen-inch refractor, but the weight of the device threatened to snap the telescope’s wooden tube. Instead, Hale affixed the apparatus to the observatory’s twelve-inch, fixed, horizontal refractor, which receives starlight via an articulated, eighteen-inch plane mirror. However, the arrangement failed. “Not only is a large amount of diffuse light sent into the spectroscope,” Hale complained, “but the distortion of the mirror by the sun’s heat soon changes a prominence into a shapeless mass when the diffuse light does not render it entirely invisible.” Frustrated by the lack of suitable equipment, Hale graduated from MIT in 1890, then sat down to design a telescope and spectrograph customized to the task at hand.

  Once again, George Hale availed himself of his father’s generosity. This time it brought to his Kenwood Observatory a gleaming twelve-inch Brashear refractor, premium Warner and Swasey mount, and ten-foot-focal-length spectrograph with an advanced Rowland grating. Rigid bracing effectively united the telescope and spectrograph into a singe, flexure-free unit. The building’s new extension, topped by a twenty-six-foot dome and flanked by a reception room, library, and spectroscopic laboratory, was dedicated on June 15, 1891, before a hundred civic and scientific luminaries. At once, Hale’s center became the nation’s best-equipped private astrophysical observatory, a worthy successor to those of Lewis Rutherfurd and Henry Draper.

  The twelve-inch refractor telescope and spectroscope in George Hale’s Kenwood Observatory, Plate II from the August 1891 issue of the Sidereal Messenger.

  Even as the dignitaries gathered, Hale could announce that his spectroheliograph had yielded spectacular results. By utilizing the brilliant violet emission lines of calcium—the color at which 1890s-era dry plates were most sensitive—exposures of two or three minutes captured panoramic portraits of the Sun as it had never been depicted before. The Sun’s seemingly placid surface, as portrayed in conventional white-light pictures, had turned into a roiling inferno of turbulent gas. In Kenwood Observatory’s first year of operation, Hale and his photographic assistant, Ferdinand Ellerman, produced fifteen-hundred photographs of solar features, both prominences fringing the Sun’s periphery and sunspots and bright regions—“faculae”—seen against the solar disk itself. (Reprising their childhood roles, George’s siblings Will and Martha obtained an excellent prominence photograph themselves while their big brother was traveling in Europe.)

  George Hale’s Kenwood Observatory, Plate I from the August 1891 issue of the Sidereal Messenger.

  News of Hale’s innovation spread quickly, as his spectroheliograms appeared in journals worldwide. In June 1891, Hale’s initial report was read before the Royal Society in London and he was elected a Fellow of the Royal Astronomical Society. The British Association for the Advancement of Science feted him at its August meeting. “I am treated like a Grand-Duke!” he wrote a friend. The burst of acclaim also brought to Hale’s doorstep the galvanic president of the new University of Chicago, William Rainey Harper. As driven to accomplishment as Hale himself, Harper had graduated from college at age fourteen, received his doctoral degree from Yale at eighteen, and now at age thirty-five, led an institution generously funded by John D. Rockefeller. Harper’s visit was not unexpected, nor was its intent. Edward Pickering had already written to Hale that Harper had been asking about him. A friend from the Astronomical Society of the Pacific forwarded a similar inquiry, remarking, “The enclosed looks like business.”

  Solar activity captured by George Hale’s spectroheliograph at the Kenwood Observatory in 1892. A circular metal plate within the instrument blocked the glare of the sun’s surface.

  Harper tried to lure Hale to Chicago’s faculty, if Kenwood Observatory came along. Hale refused, having learned that Harper was more interested in acquiring the facility and its advanced equipment than in Hale himself. But within two years, the calculus had changed. The fledgling university had demonstrated its commitment to original research: among others, the great experimentalist Albert A. Michelson had been brought on to lead the physics department. Hale also knew that the planned successor to Kenwood’s twelve-inch refractor lay well beyond his father’s means to provide. The sight of the giant Lick refractor during his honeymoon in the summer of 1890 had inspired a vision of an even larger telescope devoted to astrophysical observation. To realize that dream, he needed an institutional affiliation,
as well as William Harper’s connections. To the independent-minded Hale, an academic post was but a means to an end: “I would not consider the thing for a moment were it not for the prospect of some day getting the use of a big telescope to carry out some of my pet schemes.”

  In 1892, George Hale was appointed associate professor of Astral Physics at the University of Chicago. His contract stipulated that, if his first year proved agreeable and if President Harper established a quarter-million-dollar research and maintenance fund, Hale would transfer ownership of the Kenwood Observatory to the institution.

  While at a meeting of the American Association for the Advancement of Science, in Rochester, New York, in August 1892, Hale overheard a conversation that set his course for the next five years. Alvan Graham Clark, son of the founder of the great American optical house and the family raconteur, divulged that a pair of pristine, forty-inch glass disks from France lay in storage at the Cambridge workshop. The University of Southern California had ordered the castings in an effort to surpass the University of California’s thirty-six-inch refractor at Lick Observatory. However, the regional economy soured and the prime donor withdrew his pledge of support, leaving the record-breaking disks up for grabs. Now the American telescope maker owed the French glassmaker $16,000, with no means to pay.

  No doubt George Hale made several quick mental calculations. The light grasp of a forty-inch telescope is fully 23 percent greater than that of a thirty-six-inch. Its resolving power would render visible a quarter at a distance of three hundred miles. And the Sun’s image, a measly two inches across in the Kenwood refractor, would swell to almost seven inches. But the telescope, while useful in itself, would form the observational hub of a world-class astrophysical laboratory.

  After declaring his urgent interest to Alvan Graham Clark, Hale hopped the next train back to Chicago and urged President Harper to strike the deal that would bring the world’s largest telescope to the University of Chicago. In a single, timely bound, Hale told him, the institution would vault to the top of the scientific establishment. The estimate for the telescope, mount, accessory equipment, and building: $300,000.

  Harper had allocated the university’s initial endowment to the establishment and staffing of the various academic departments. A massive expenditure toward the sort of highly specialized research facility that Hale envisioned would have to come from a new funding source. As distasteful as it must have been, Harper scheduled a meeting on October 2, 1892, with streetcar magnate Charles T. Yerkes. A “strange combination of guile and glamour,” according to one observer, Yerkes wasn’t called the “Boodler” for nothing. Once jailed in Philadelphia for embezzlement and notorious in Chicago for all manner of business chicanery, Yerkes had previously promised, then abruptly withdrew, his support for a new biology building. He received Hale’s pitch enthusiastically, swooning over the size and power of the proposed telescope, as well as having his name affixed to the landmark instrument. Cost be damned, his goal was to “lick the Lick.”

  So began George Hale’s five-year struggle to keep his new observatory on the rails. Almost immediately, Yerkes retreated from his original agreement to fund the entire project down to its last nut, bolt, and brick. Hale, he claimed, had misconstrued the terms: he was financing only the telescope itself, not the building, astrophysical laboratories, or associated equipment. Having no sense of the price associated with optical and mechanical refinement, he accused Hale of ginning up costs and creating a scientific edifice where a modest facility would do. (In fact, it was Yerkes, not Hale, who hiked the architectural splendor of the building.) Only after repeated entreaties and overt appeals to vanity did Hale coax Charles Yerkes to fund the observatory to its completion.

  The Yerkes Observatory rose on the shores of Lake Geneva in Williams Bay, Wisconsin, a once-dark exurb eighty miles northwest of Chicago. (Hale favored a California mountaintop, but Charles Yerkes refused.) The stately, Romanesque-style building is shaped like a Latin cross, with the ninety-foot dome of the big refractor anchoring its base, and a pair of smaller domes and a meridian-telescope room at the remaining cardinal points. Laboratories, offices, optical and machine shops, a library, and a lecture hall occupy the structure connecting the observatories. On May 19, 1897, the precious lenses arrived at Williams Bay station in a private Pullman car, accompanied by Alvan Graham Clark and his shop foreman Carl A. Lundin. Within a day, installation was complete.

  The Yerkes Observatory in the 1890s. The large dome at right houses the forty-inch refractor.

  The half-ton achromatic objective, pairing a two-and-a-half-inch-thick crown-glass lens with a one-and-a-half-inch-thick flint-glass lens, sits at the upper end of a sixty-three-foot-long sheet metal tube. The telescope and its movable parts weigh in at twenty tons, yet the tube is moved by the gentle impulse of a hand or an electric motor. The entire assembly rests atop a cast iron column, forty-three feet high, which itself is secured to a brick-and-concrete base. A thirty-seven-ton, counterpoised floor conveys the observer to the eyepiece, whose elevation varies by twenty-three feet depending on the telescope’s orientation. (The floor collapsed when a support cable slipped from its pulley a few nights after observations had commenced. No one was hurt and the telescope was unharmed.)

  On the night of May 21, 1897, after a thorough viewing of the planet Jupiter, George Hale, Edward Barnard (whom Hale had hired away from Lick), and observatory assistant Ferdinand Ellerman swung the new telescope toward deep space. The Ring Nebula in Lyra and the Dumbbell Nebula in Vulpecula shimmered with remarkable clarity, and the globular star cluster in Hercules seemed more populous than ever. Without question, Barnard pronounced, the celestial scenes surpassed those of the Lick refractor. Several days later, Hale reassured the project’s mercurial benefactor that his “telescope is not only the largest but also the most powerful in the world.”

  The forty-inch refractor of the Yerkes Observatory, photographed in 1925.

  While the observatory struggled to prosper—Charles Yerkes provided no operating funds—Hale’s enthusiasm and heroic fund-raising efforts buoyed the disposition of the staff. Those who worked alongside him describe an almost palpable creative energy that transcended the muted confines of scientific investigation. Astronomer Frederick Hanley Seares noted that Hale’s “logical formulation was shaped by the imaginative powers of a temperament essentially artistic. Problems thus presented became something engaging, to be undertaken as adventures of the spirit; and to Hale they were indeed such adventures, entered upon with a kind of joyous gaiety.”

  At Yerkes, Edward Barnard, now professor of Practical Astronomy, tracked the movements of planetary satellites and continued his wide-field photography of the Milky Way. Dartmouth College spectroscopist Edwin B. Frost was brought on to measure stellar radial velocities using a precision spectrograph funded by the noted astronomical benefactress, Catherine Wolfe Bruce. Hale’s longtime friend Sherburne Burnham opted to keep his job at the courts, but arrived at Williams Bay station nearly every Saturday afternoon with a box of cigars under his arm and a case of Burgundy in waiting. For the next two nights, he measured double stars with the forty-inch, then returned to Chicago on the early Monday train. Walter S. Adams, Frost’s graduate student at the time, joked that on the morning after Burnham’s shift, “a fairly accurate analysis of his observing schedule could be made from the intricate trail of tobacco ashes on the floor of the dome.”

  From 1903 to 1905, Columbia University graduate Frank Schlesinger used the big refractor to conduct an exhaustive study of the instrumental and atmospheric factors that affect the photographic measurement of stellar parallax. The methods he derived at Yerkes were adopted at other observatories and became the basis for the General Catalog of Stellar Parallaxes, published in 1924. George Willis Ritchey, the staff optician, utilized special filters and photographic plates to effectively negate the telescope’s chromatic aberration and turn the instrument into a formidable astronomical camera. Double stars that eagle-eyed Burnham had see
n only under prime conditions were now imaged on a regular basis. The populous cores of globular star clusters were recorded in crisp definition. A half-second, high-magnification exposure on October 12, 1900, of the lunar crater Theophilus projected a vertiginous sensation of depth.

  Secluded Williams Bay conveyed a sometimes serene, sometimes oppressive sense of isolation. Groceries were brought in daily by train, fresh meat twice a week if ordered ahead. Distant echoes of outside events wafted in, muted both by the observatory’s remoteness and the astronomers’ overriding focus on their scientific work. “This is a very peaceful region of the world,” Hale said, “where we occasionally hear faint rumors of disturbance, but are not much concerned with such doings ourselves.” A sense of exclusivity infused the premises, a selfless nobility of mission enveloped the staff. One astronomer, in a half-serious expression of Yerkes’s special status, had his students and academic friends utter the password “syzygy” (an alignment of celestial bodies) before being admitted to the sanctum of the observatory.

  During the warmer months, Williams Bay was a rural paradise, offering golf, sailing, hiking, and the simple pleasure of unhurried contemplation. The summer mansions of wealthy Chicagoans lined the shores of Lake Geneva, whose waters hosted a zigzag flotilla of steamers and small yachts. Hale and his family lived in a gracious house overlooking the lake; staff members’ families resided in smaller homes on the observatory grounds or nearby. Bachelors and visitors lodged at a local rooming house. Transportation, when not by foot, was by horse-drawn carriage, the rutted roads an obstacle course to bicycles. As winter closed in, the village became an outpost, with blistering winds, chest-high snow, and howling wolves. Hale’s wife and children spent the winter months in a rented apartment in Chicago, seeing him only on weekends.