The Glass Universe: The Hidden History of the Women Who Took the Measure of the Stars. Дава Собел
bouts of altitude sickness with an effective local remedy, namely the odor of bruised garlic. No particular peak impressed Bailey as ideal, but he needed to seize the good weather of the dry season, and so settled for a nameless mountain with the least obstructed view. It stood just over 6,500 feet high, barely accessible by a path that switchbacked up and around for eight miles. The Baileys labored alongside a dozen locals for three weeks to improve the route from the hotel in Chosica to the site, and then helped drag eighty loads of equipment up that road to the makeshift observatory. When the family moved in on May 8 along with their Peruvian assistant, two servants, cats, dogs, goats, and poultry, their only neighbors were centipedes, fleas, scorpions, and the occasional condor. They relied on a muleteer for daily supplies of water and food.
The Baileys assessed the brightness of the southern stars with the same meridian photometer that Pickering had used in Cambridge, in order to make their observations exactly comparable to his. Similarly, they photographed the southern stellar spectra for the Henry Draper Memorial with the selfsame 8-inch-aperture Bache telescope that had seen nightly duty through the project’s first two years. Mrs. Draper replaced the original workhorse at Harvard with another of the same specifications.
Solon Bailey stayed in touch with Pickering as regularly as the mails allowed. When he shipped the first two cases of glass plates to Cambridge, he said they came from an as yet unnamed place that he would like to call Mount Pickering.
“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.
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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.
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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”