The Glass Universe

by Dava Sobel

  “Mt. Pickering might wait,” the director wrote back on August 4, 1889, “until I have done as good work as you have on a Peruvian mountain.” With local approval, the Baileys christened the site Mount Harvard instead.

  When the October onset of the rainy season halted work on Mount Harvard, Bailey moved his wife and son to Lima, then set off with his brother to scout better locations for a permanent base. It took them four months to find a place that met their requirements, on the high desert plain near the town of Arequipa. At 8,000 feet, the air was clear, dry, and steady, and the nearby volcano, El Misti, was nearly extinct.

  • • •

  WHILE THE BAILEYS EXPLORED PERU, Edward Pickering became engrossed with the odd spectrum of a star called Mizar in the handle of the Big Dipper. The star had first drawn his surprised attention on a Draper Memorial photograph taken March 29, 1887, which showed an unprecedented doubling of the spectrum’s K line. (Although Fraunhofer’s original lettering ended at I, later researchers added other labels.) Soon after Pickering shared the unusual news with Mrs. Draper, the strange effect vanished as suddenly as it had appeared. Subsequent images of Mizar’s spectrum failed to recover the double K line, but still Pickering kept watching for its return. On January 7, 1889, Miss Maury saw it, too. Pickering, who rarely invoked an exclamation point, wrote Mrs. Draper, “Now it seems nearly certain that it is sometimes double and sometimes single!” Although, he quickly added, “It is hard to say what this means.” He suspected that Mizar, also known as Zeta Ursae Majoris, might turn out to be two stars with virtually identical spectra, too closely aligned to be seen separately, even through a big telescope.

  Miss Maury could picture the Mizar pair as two wary combatants, circling each other while vying for advantage. Her distant vantage point made it difficult to distinguish the two separate bodies—impossible, in fact, when either one stood in front of the other along her line of sight. But Mizar’s twin fighters were emitting light. As they revolved, their relative motions slightly altered the light’s frequency: the approaching starlight shifted slightly toward the blue end of the spectrum, the receding starlight toward the red. Those shifts added up to the small K-line separation that created the doubling effect.

  Pickering and Miss Maury tracked Mizar’s K line through months of ambiguous changes, until they saw the doubled line again on May 17, 1889. Photographs taken a few nights before and after the doubling portrayed the line as hazy—somewhere between single and double. Miss Maury had been wise to trust her intuition about hazy lines.

  That Sunday, on her day off, Miss Maury wrote to her aunt, Ann Ludlow Draper, the wife of Henry’s brother Daniel. Everything she reported in her long, chatty letter seemed to touch on the theme of single and double. On a visit to the Boston Public Garden she had seen “a wonderful display of tulips single and double of all colors.” She now had dual Vassar Alumnae Association membership in both the Boston and New York branches. “I told them I should have a chance to vote twice but they didn’t seem to be afraid.” She saved the most interesting case for last:

  “Tell Uncle Dan that the other day Prof. Pickering succeeded in photographing the double K line of Zeta Ursae Majoris. Other lines were also double that at times are single so I suppose his theory is proved that the change is due to the rotation of two close stars of the same type around one another. It is a very pretty thing. They have been trying for months to catch it double. Prof. Pickering thinks its period must be about fifty days but has not finished the calculations yet. Of course nothing ought to be said about it publicly till it is all worked out.” She signed the letter “With love, Antonia.”

  Pickering wrote a report of the preliminary results, making sure to credit “Miss A. C. Maury, a niece of Dr. Draper” for her careful study of Mizar’s spectrum. He sent the paper to Mrs. Draper, who carried it to Philadelphia for the annual meeting of the National Academy of Sciences, where their mutual friend George Barker read it aloud to the assembly on November 13, 1889. Barker assured Pickering that the K-line news “awakened a lively interest.”

  A few weeks later, on December 8, with Mrs. Draper present at the observatory, Mizar’s K line doubled again, right on schedule. Within days, Miss Maury found the double K line in another star, Beta Aurigae (the second brightest in the constellation of the Charioteer). Now there were two examples of newfound star pairs that had been discovered by their spectral characteristics alone. And before the week was out Mrs. Fleming identified a third suspected “spectroscopic binary” on several plates from Peru.

  “Now if all these results ensue in consequence of your recent visit here,” Pickering cajoled Mrs. Draper, “is it not a sufficient argument in favor of your coming oftener?”

  Mrs. Draper wished she might flatter herself, she replied, “that the interesting results obtained during my visit were in consequence of my being with you; my friends have often called me a ‘Mascotte’ but I fear my luck will not extend so far.” Nevertheless she declared herself “delighted” with the new finds. Additional examples would help convince certain members of the Academy, present at the recent meeting, who “thought our imagination had run away with us.” More confirmation came in an independent discovery of another spectroscopic binary, also in late 1889, by Hermann Carl Vogel of the Potsdam Observatory.

  Vogel had been using spectroscopy to answer a different question—not What are stars made of? or How can stars be divided into groups? but How fast do they move toward or away from Earth in the line of sight? By the degree to which certain lines in their spectra shifted toward blue or red, Vogel calculated their radial velocity. Some traveled as fast as thirty miles per second, or well over one hundred thousand miles an hour.

  As Miss Maury continued to chart the spectral changes of Mizar, she concluded that its component stars orbited their common center of gravity once every fifty-two days. She deduced an even shorter period of only four days for Beta Aurigae, the spectroscopic binary that she had discovered. Indeed, she could watch the Beta Aurigae spectrum change from one photograph to the next over the course of a single night. She calculated the orbital speeds in the two binary systems. “A mile a minute” sounded rapid to her ear, but these stars were racing around at more than a hundred miles a second. Her uncle Henry had looked to the spectra to uncover the stars’ chemistry, and now the spectra were also yielding the stars’ celerity.

  • • •

  THE YEAR 1890 SAW THE PUBLICATION of Mrs. Fleming’s opus, “The Draper Catalogue of Stellar Spectra,” in volume 27 of the observatory’s Annals. Pickering rewarded her with a raise in salary and full acknowledgment in his introductory remarks: “The reduction of the plates was begun by Miss N. A. Farrar, but the greater portion of this work, the measurement and classification of all the spectra, and the preparation of the Catalogue for publication, has been in charge of Mrs. M. Fleming.” She styled herself “Mina Fleming” now. In addition to the dedication she had shown in measuring and classifying the spectra of ten thousand stars, she had also expertly proofread the catalogue’s four hundred pages. Most of the pages consisted of tables, twenty columns wide and fifty lines long, representing approximately one million digits in all.

  The Draper Catalogue sorted the stars by the appearance of their spectral lines—not merely for the sake of sorting, but in the hope of opening new avenues of investigation. The classification inspired Pickering, for one, to analyze the distribution of stars by spectral type. Peering into the luminous band of the Milky Way, he found a preponderance of B stars. The B stars clustered along the Milky Way as though they had an affinity for one another or for that region of space. The Sun, a G star, seemed to Pickering to have little relation to the lights of the Milky Way.

  Meanwhile Miss Maury proceeded with her own elaborate classification system. She intended to increase Mrs. Fleming’s fifteen classes to twenty-two, and also subdivide each type into three or four subcategories, based on the further gradations she detected in the spectra
of her bright stars. The strain on her vision prompted her to consult a Boston oculist, who prescribed eyeglasses.

  “Dear Auntie,” she wrote to her great-aunt Dorothy Catherine Draper on February 18, 1890, “I am now writing up the results of my work of the last two years. I have made a short outline that is the beginning of my classification. I was very much afraid Prof. Pickering would not like it, but I am glad to find that he is quite satisfied and says with a few changes it will do to print. Of course it will take me a long time to get the whole thing written and I expect all the details will make quite a volume. . . . I wear your black hat every day and your afghan keeps me warm at night.”

  In his fourth annual report of the Henry Draper Memorial, published shortly after Mrs. Fleming’s catalogue in 1890, Pickering announced that the total number of photographs taken with the various telescopes had reached 7,883. Other observatories, he noted, made the “very common mistake” of accumulating photographs without deriving results from them through discussion and measurement. At Harvard, however, a corps of computers had been studying the photographs for several years, so that “for many purposes the photographs take the place of the stars themselves, and discoveries are verified and errors corrected by daylight with a magnifying-glass instead of at night with a telescope.” Here, too, as in the Annals, he cited both Mrs. Fleming and Miss Maury by name. It was the niece of Henry Draper, he emphasized, who had discovered the doubling of the lines in Beta Aurigae.

  In line with his usual practice, Pickering distributed the fourth annual report of the Henry Draper Memorial far and wide, including publication in Nature and other scientific journals. The report found one of its most appreciative audiences in England, at the home of astronomer and military engineer Colonel John Herschel. As a grandson of William Herschel (discoverer of the planet Uranus) and a son of Sir John Herschel (thrice president of the Royal Astronomical Society), the colonel had seen his share of important leaps in celestial knowledge.

  “I have just rec’d your last H. D. Mem. report,” he wrote to Pickering on May 28, 1890. “It is very like a pudding all plums—but I will ask you to convey to Miss Maury my congratulations on having connected her name with one of the most notable advances in physical astronomy ever made.”

  Like the colonel’s much celebrated great-aunt, Caroline Herschel, Miss Maury had entered a field of discovery dominated by men, yet she stood among the first astronomers to detect an entirely new group of objects through the upstart method of spectral photography. Its future—and hers—seemed full of promise.

  CHAPTER THREE

  Miss Bruce’s Largesse

  EVEN BEFORE SOLON BAILEY selected the site for Harvard’s Southern Hemisphere observatory, Edward Pickering had envisioned a superb new telescope to mount there. This ideal instrument would have a lens 24 inches in diameter, or triple the size of the trusty 8-inch Bache, and would therefore gather nine times as much light. He estimated the cost of manufacture at $50,000. In November 1888 he issued a general appeal for the needed funds, and, as in a fairy tale, another heiress stepped forward to grant his wish.

  Catherine Wolfe Bruce lived in Manhattan, not far from Anna Draper, but the two were unacquainted before their fortunes crossed in the Harvard Observatory. Miss Bruce, more than twenty years older than Mrs. Draper, had no practical experience with telescopes of any kind. She was a painter and a patron of the arts. Although she lacked Mrs. Draper’s knowledge of astronomy, she had long nurtured a vague, distant interest in the subject. Now, at seventy-three, she evinced a genuine eagerness to support further research in the field. As the eldest surviving child of the successful typefounder and print innovator George Bruce, she controlled the disbursement of his wealth. In 1888 she paid $50,000 to erect the George Bruce Free Library on Forty-second Street and fill it with books. An equal expenditure on a single scientific instrument did not seem unreasonable to her, especially the way she heard Pickering describe it when he called on her at home on the morning of June 3, 1889. The large photographic telescope of his dreams, he informed her, would be the most powerful ever pointed at the sky. Dispatched to some lofty mountain for unimpeded, unceasing work, it promised to enrich humankind’s knowledge of the distribution and constitution of the stars, far beyond the combined capabilities of numerous—even much larger—telescopes of more typical design.

  Perhaps Pickering’s reference to the 24-inch object glass as a “portrait” lens appealed to Miss Bruce’s artistic sensibility. Surely his optimistic enthusiasm provided an antidote to the disquieting article she had recently read by astronomer Simon Newcomb, director of the U.S. Nautical Almanac Office and professor at the Johns Hopkins University. Professor Newcomb predicted that no exciting astronomical finds would turn up in the near or even the distant future. Since “one comet is so much like another,” he asserted “that the work which really occupies the attention of the astronomer is less the discovery of new things than the elaboration of those already known, and the entire systematization of our knowledge.”

  Miss Bruce viewed the matter differently. Nowhere had she seen a complete list of the ingredients of stars, nor did anyone seem to know what made them shine, or how they formed in the first place. The more she read, the more questions occurred to her. What occupied the spaces between the stars? How could Professor Newcomb call the knowledge complete? As she judged astronomy’s prospects, the introduction of photography and spectroscopy, along with advances in chemistry and electricity, suggested that major new findings were afoot. She was counting on Professor Pickering to prove her right, and within weeks of his visit she sent him the requisite sum of $50,000.

  As Pickering expressed his thanks to Miss Bruce, he assured his other benefactress that her project, the Henry Draper Memorial, would reap great rewards from the acquisition of the Bruce telescope—at no added cost to the Draper fund.

  Mrs. Draper’s beloved 28-inch telescope, like the 11-inch before it, had been installed in its own new domed building at the observatory. Although it was the largest of the four telescopes she donated, and the one she had been the most reluctant to part with, it was not living up to expectations. Willard Gerrish, the observatory’s talented and innovative tinkerer, along with George Clark, the telescope maker, had spent the first few months of 1889 fussing with it, trying various configurations and adjustments, but wrested from it only a single good spectrum of a faint star. These frustrating experiences increased Pickering’s admiration for Dr. Draper’s skill, but also forced him to admit defeat, and he abandoned further experiments with the instrument. Mrs. Draper, disappointed but understanding, joined the Pickerings that summer for a short vacation in Maine.

  Miss Bruce made no plans to visit Cambridge, as she rarely left home. (“Rheumatism and Neuralgia have racked me badly,” she explained.) Nevertheless she followed every step of the telescope’s progress via close correspondence with Pickering, beginning in mid-1889, when he ordered the four large lens disks from the firm of Edouard Mantois in Paris. Miss Bruce had learned about glass in her salad days, while collecting art and antiquities on travels throughout Europe. Immersed now in her astronomy self-education, she found the lens for the new telescope preoccupied her as no figurine or chandelier ever had.

  “I bought [Charles] Young’s Elements of Astronomy,” she told Pickering, “after reading in a newspaper that it was adapted to the humblest capacity—Well there is in ‘every lowest depth a lower deep’ and I fear to fall into it.

  “Young calls the vast spaces between the stars a vacuum,” Miss Bruce continued, while another book she read by philosopher John Fiske “speaks of it as the luminiferous ether. I shall hold on to Young.” Pickering obligingly provided her with all the Harvard Observatory’s publications, from volumes of the Annals to offprints of his research reports. “Your paper on Variable Stars of Long Periods,” she said in a thank-you note, “I at once read and with admiration— not of the Tables but of the simple goodness of heart shown in the detailed direction
s to unskilled amateurs how to become useful aids to Science.”

  Since his initial 1882 open invitation to amateurs, especially ladies, to observe the changing brightness of variable stars, Pickering had repeated the request with relevant instructions, and also rewarded the volunteers by publishing several summaries of their results in the Proceedings of the American Academy of Arts and Sciences. He recommended that amateurs follow only those variables that cycled slowly through their brightness changes over periods of days or weeks, and leave the more rapid or erratic examples to study by professionals. No amount of amateur assistance, however, relieved Pickering of the need to repeat his exhortations for additional funding in every annual report of observatory activities.

  Upon hearing that certain millionaires had failed to open their pocketbooks in response to a worthy appeal, Miss Bruce reminded Pickering that “some generalship is required” in dealing with rich gentlemen: “They must not be attacked directly and squarely but in flank or rear.” For her part, she volunteered to lend further assistance, not just to Harvard, but to astronomers everywhere, if Pickering would agree to help her choose the most deserving cases. With her promise of $6,000 to start, he announced a call for aid applications in July 1890. He also sent letters to individual researchers at observatories all over the world, asking whether they could put $500 to immediate good use—say, to hire an assistant, repair an instrument, or publish a backlog of data. Nearly one hundred responses met the October deadline. Pickering evaluated the proposals and Miss Bruce approved his recommendations in time for a November selection of the winners. Simon Newcomb, author of the article that had aroused Miss Bruce’s indignation, became one of the first five scientists in the United States to receive her support. Another ten awards went overseas to astronomers working in England, Norway, Russia, India, and Africa.