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,
