by Dava Sobel
In March 1923 Margaret Harwood of the Nantucket observatory went to Arequipa to aid the Baileys. She took photographs through the Bruce telescope for Solon and also gave Ruth the benefit of her postwar experience with the Home Service of the American Red Cross. “I enjoy the work here very much,” she wrote Shapley in June. “I now work with the Bruce the second half of the night. The dome works easily enough and so does the telescope. . . . This is a lovely spot. So far I have found only three kinds of ants, and they do not look very unlike New Englanders, but you may know better when you see the specimens.”
By August Mrs. Bailey, still unable to speak or write clearly, was advised to go home, as the chances for her full recovery looked better at sea level. She went to stay with her son and daughter-in-law in Cambridge until her husband could join her.
Shapley’s ongoing search for a new southern director led him to the Yerkes Observatory in Wisconsin, where Dorothy Block, the second Pickering Fellow, had found employment after leaving Harvard. At Yerkes, Miss Block fell in love with visiting astronomer John Stefanos Paraskevopoulos. After they married, she moved with him to his native Greece. The newlyweds were working together at the National Observatory of Athens when Shapley tapped them to take over the Arequipa station. Dr. and Mrs. “Paras” reached Peru in December 1923, freeing Bailey to go home at last. The circle of his longtime friends in the region bid him good-bye with the parting gift of an honorary doctor of science degree from the ancient University of San Agustin, along with an honorary title as professor of astronomy.
The energetic young Parases overcame the cloudy season in Arequipa by temporarily relocating the observatory. They carried two of the telescopes to a site near Chuquicamata in northern Chile, at an altitude of 9,000 feet. There they took large numbers of photographs under clear, dark skies, until April came and rendered Arequipa desirable again.
The shortened observing season in Arequipa made Shapley revisit Pickering’s idea of transferring the Boyden Station to a new site in South Africa, but budgetary restraints prohibited such action. Shapley first had to meet the observatory’s more pressing needs. Private donations from George Agassiz and other members of the Visiting Committee enabled the director to install an automatic sprinkler system in the Brick Building. Although Pickering had judged the building’s brick exterior an ample safeguard against fire, Shapley feared its wooden floors, shelves, plate cases, desks, and other office furniture posed flammable threats to the treasured glass images.
“Since the first photograph of a star was made at Harvard in 1850 under the supervision of Professor George P. Bond,” Shapley reminded President Lowell, “the Observatory has been a repository for an ever-growing collection of astronomical photographs.” The building now housed nearly three hundred thousand glass plates. “The photographs made before 1900 are especially serviceable in the study of stellar motions and variability, and they are, of course, irreplaceable, and are unduplicated at other observatories.” To the relief of uneasy astronomers, the new sprinklers finally gave the collection the protection it deserved. Tests of the system proved that water gushing from the sprinklers would do no damage to the glass universe, which was now further shielded inside new metal cabinets—dust-tight, mold-resistant, and moisture-proof.
What the observatory needed next were three or four more assistants to probe the plates. As soon as Miss Ames completed her fellowship year, in January 1924, Shapley hired her to fill Henrietta Leavitt’s still-vacant place on the staff. No matter that Radcliffe College would not confer the master of science degree on Miss Ames until commencement day in June. She was ready now to help Shapley search the arms of the spiral nebulae for evidence of star formation. One thousand new spirals had just turned up in a single recent photograph taken by Bailey at Arequipa through the Bruce telescope.
Shapley pushed Miss Payne to go beyond the master’s stage—to carry her original research all the way through to a Ph.D. Only a few other female astronomers had won this rare accolade, from universities in New York, California, and Paris; Miss Payne would be Harvard’s first. Already she had drawn significant, publishable results from her studies. She was about to submit a report on the spectra of the hottest stars to Nature, under the name C. H. Payne, when Shapley challenged her by asking, “Are you ashamed of being a woman?” The question induced her to change her author identity to Cecilia H. Payne. Weeks later, when another of her finds struck Shapley as grist for another publication, he rushed her to prepare a paper right away, to be submitted in time for the next day’s posting deadline. In his eagerness he even volunteered to type it for her. “What a glorious evening!” Miss Payne proclaimed her impromptu partnership with the D.D. “I wrote, he typed, far into the night. Into the mail it went. And I walked back to my room in the dormitory in a dream. My feet did not seem to touch the ground . . . it was almost like flying. I had not wanted to tell him that I was quite a good typist myself.”
Miss Payne happened to be in Shapley’s office the day he received a letter, dated February 19, 1924, from Edwin Hubble, a former colleague of his at Mount Wilson. “Dear Shapley,” it began. “You will be interested to hear that I have found a Cepheid variable in the Andromeda Nebula.” Few announcements could have rattled Shapley more than this one. The Andromeda Nebula, dimly visible to the naked eye, was the largest, most closely observed of all the spirals. A nova had erupted at its heart in August 1885, but was never captured on glass, given the primitive state of celestial photography at that early date. Since then the Andromeda Nebula had borne no evidence of individual stars, either at its center or anywhere along its spiral arms. Shapley’s friend Adriaan van Maanen, who had measured Andromeda’s rotation, swore he saw the nebula spinning rapidly, which meant it must lie relatively nearby—near enough for its individual stars to be seen if any such existed. Now Hubble, in a series of long exposures made on consecutive nights with the 100-inch telescope, had revealed whole congeries of stars in Andromeda.
“I have followed the nebula this season as closely as the weather permitted,” Hubble’s letter said, “and in the last five months have netted nine novae and two variables.” The light curve he constructed for one of the variables showed the slow dip and rapid rise to maximum brightness characteristic of Miss Leavitt’s Cepheid stars. Hubble’s newfound Cepheid peaked near the very faint magnitude of 18, though its long period of thirty-one days decreed it must be thousands of times brighter than the Sun. The star appeared dim only by dint of great distance. Using Shapley’s own calibration for the Cepheids, Hubble placed the Andromeda spiral more than a million light-years away. For the nebula to loom so large across a chasm that wide, it had to rival the Milky Way in size. Therefore the Andromeda Nebula must be a galaxy—an island universe—in its own right.
After Shapley read Hubble’s news and looked at the light curve, he held out the pages to Miss Payne, saying, “Here is the letter that has destroyed my universe.”
In a “Dear Hubble” reply of February 27, Shapley sounded unwilling to admit defeat just yet: “Your letter telling of the crop of novae and of the two variable stars in the direction of the Andromeda nebula is the most entertaining piece of literature I have seen for a long time.” Rather than situate the variables within the nebula, as Hubble claimed, Shapley allowed only that they lay in that general direction.
Shapley had never much liked Hubble. Both men were Missouri-born, but Hubble, after spending three years as a Rhodes scholar at Oxford, had exchanged his midwestern twang for an affected British accent. He also clung to the military rank he had achieved in the army during the Great War, so that he continued to introduce himself as Major Hubble in civilian life. When, at Hale’s invitation, the major reported to Mount Wilson in September 1919, he came dressed in jodhpurs and a cape. During the short period in which Shapley and Hubble observed on the same mountaintop, the one winced every time the other said “Bah Jove!” Even so, Shapley judged Hubble’s meticulous work to be beyond reproach: “The distanc
e of your variable from the nucleus and the lovely number of plates you have now on hand,” Shapley conceded in his letter, “of course assures you of genuine variability for these stars.”
Hubble had intended the news of the Cepheid for Shapley’s eyes only, as he planned to confirm the Andromeda distance by further observations before making a public statement. The week after he dispatched his bombshell, however, Hubble took time off to marry Stanford University graduate Grace Burke Leib, a wealthy widow from Los Angeles, and honeymoon with her for three months in Europe. When he returned to work he turned up eleven more Cepheids in Andromeda. Shapley had once worried that eleven “miserable” Cepheids in the Milky Way lent insufficient support to his Big Galaxy. Now Hubble’s dozen in Andromeda dealt the lone-galaxy idea a decisive blow. Hubble’s Cepheids discredited van Maanen’s measurements of rapid spiral rotations. Indeed, Hubble’s Cepheids populated the cosmos with multiple “island universes.”
“After Hubble’s discovery of Cepheids,” van Maanen wrote to Shapley, “I have been playing again with my motions and how I look at the measures.” He continued to believe in them, though others ceased believing.
Heber Curtis, Shapley’s former “debate” opponent, reveled in the proven reality of the island universes. Writing in Scientia in 1924, Curtis thrilled at the implications of the new insights: “Few greater concepts have ever been formed in the mind of thinking man than this one, namely,—that we, the microbic inhabitants of a minor satellite of one of the millions of suns which form our galaxy, may look out beyond its confines and behold other similar galaxies, tens of thousands of light-years in diameter, each composed, like ours, of a thousand million or more suns, and that, in so doing, we are penetrating the greater cosmos to distances of from half a million to a hundred million light years.”
A human being might not be “such a big chicken,” as Shapley had gibed in 1918 when he moved the Sun far away from the Milky Way’s center, and yet, the human mind could traverse space and time.
• • •
CECILIA PAYNE PATIENTLY SIFTED the same objective-prism plates that had passed through the hands of Nettie Farrar, Williamina Fleming, Antonia Maury, and Annie Cannon. In the runic line patterns, which had helped her predecessors sort the stars into categories, Miss Payne read a new subtext. It concerned the actions of individual atoms, absorbing and releasing tiny quantities of light. Each spectrum’s thousands of Fraunhofer lines registered the leaping of electrons from one energy level to another as they orbited atomic nuclei.
Miss Payne’s vision was informed by the work of Indian physicist Meg Nad Saha of Calcutta, the first person to link the atom to the stars. In 1921 Saha demonstrated that the various classes of stars displayed their distinctive spectral patterns because they blazed at different temperatures. The hotter the star, the more readily the electrons around its atoms leapt to higher orbits. With enough heat, the outermost electrons broke free, leaving behind positively charged ions with altered spectral signatures. Saha created mathematical equations for predicting the locations of Fraunhofer lines in the spectra of various elements at extremely high temperatures—higher than could be achieved in laboratory furnaces. Then he fit his predictions to published spectra from the Harvard collection. The matches suggested that the categories of the Henry Draper classification depended almost entirely on temperature. The O stars were hotter than the B, which were hotter than the A, and so on, all the way down the sequence to its end.
Other investigators, from early classifier Angelo Secchi to current theorist Henry Norris Russell, had likewise noted the correlation between temperature and star type, but no one before Saha ever provided a physical mechanism for it. From the placement and intensity of certain Fraunhofer lines, Saha could estimate actual temperature ranges for stars in the various Draper categories.
Following Saha’s promising lead, Edward Arthur Milne, one of Miss Payne’s instructors at Cambridge, had reformulated and improved his techniques. Milne and his associate Ralph Fowler derived different stellar temperature values, though still in the order of the Harvard system. Fowler and Milne also factored in much lower pressures for stellar atmospheres than Saha had assumed, given that the gases around stars found ample room in which to spread thin. Compared with the air pressure at the surface of Earth, the minuscule atmospheric pressure of a star might be measured in the tiniest fractions of ounces per square inch, and these rarefied conditions would increase the tendency of atoms to ionize.
By 1923 Fowler and Milne had solidified the connection between atomic transitions and the intensity of corresponding Fraunhofer lines. A new research direction now lay open: By closely inspecting the strengths of the lines through the various spectral classes, a careful analyst might extract the comparative abundance of each component element. The raw material for making such revelations already existed in America, in the plate vaults in Cambridge and Pasadena. When Miss Payne departed Newnham College for the Harvard Observatory, Milne urged her to mine its glass photographs for spectra that would test and verify the Saha theory. “I followed Milne’s advice,” said Miss Payne, “and set out to make quantitative the qualitative information that was inherent in the Henry Draper system.”
Princeton’s Henry Norris Russell felt drawn to the same pursuit. Since Princeton lacked the needed resources, Russell arranged for extended leave periods on Mount Wilson, and sent one of his graduate students, Donald Menzel, to examine the plates at Harvard. Menzel’s training in laboratory spectroscopy complemented the atomic knowledge Miss Payne brought to bear, but the two did not collaborate.
“I pressed on alone,” Miss Payne wrote of her early struggle. “It was clear that some quantitative method must be devised for expressing the intensities of spectral lines, and I set up a crude system of eye estimates. Next came the identification of the line spectra, the selection of known lines for examination, and the arduous task of estimating their intensities on hundreds of spectra.” Often she felt bewildered. She tasted her first breakthrough with the spectral lines of the element silicon, which she detected among the hottest stars, and in four successive stages of ionization (from neutral atom to the loss of one, then two, and finally three electrons). With these observations she calculated the heat required to remove the electrons, and thereby determined the temperatures of O stars to range from twenty-three thousand to twenty-eight thousand degrees.
Sometimes Miss Maury, who also liked to work late at night, stopped in with tidbits from her current spectral study of the southern binary stars. The women’s pleasurable discussions were “painfully punctuated by insect bites,” Miss Payne said, because Miss Maury insisted on keeping the windows open but could not bear to kill the mosquitoes.
Element by element, Miss Payne estimated, plotted, and calculated her way through the spectra to take the temperatures of the stars. All of her figures described the heat of the stellar atmospheres—the stars’ visible, superficial layers that gave rise to their spectra. Temperatures deep inside the stars could only be conjectured. No one knew the processes by which stars generated their great power.
Shapley, intent on seeing Miss Payne garner Harvard’s first doctoral degree in astronomy, organized a formal faculty committee to draft a preliminary written examination for her. She passed the test on June 10, 1924. As an official candidate for the Ph.D., Miss Payne attended summer astronomy meetings in New Hampshire and Ontario, wondering all the while where she would find the money to continue her study. The Pickering Astronomical Fellowship expired after just one year, with no provision for renewal.
At the August gathering in Toronto of the British Association for the Advancement of Science, Miss Payne reencountered her first idol, Arthur Stanley Eddington, and also Edward Arthur Milne. They warned her that astronomy opportunities for women in England had not improved, and she should remain on this side of the Atlantic if at all possible. Fortunately, Miss Payne, by virtue of being a female college graduate, younger than thirty, who wished t
o study in the United States while still the citizen of a foreign country, met every qualification for the Rose Sidgwick Memorial Fellowship of the American Association of University Women. The $1,000 she won in September from this source secured her second year at Harvard.
Resuming her measurements of stellar temperatures, Miss Payne also teased out the relative proportions of elements in the various types of stars. Whereas her temperature determinations had been hard-won but satisfying in their agreement with previous ideas, the new figures for abundances alarmed her. Given that stars consisted of the same ingredients that constituted Earth’s crust, most astronomers supposed that the recipe proportions must also agree. Common earthly substances, such as oxygen, silicon, and aluminum, were expected to prove just as prevalent among the stars. Miss Payne’s calculations in fact revealed that kind of correspondence for almost every material, save for two notable exceptions, hydrogen and helium, the two lightest elements. Hydrogen abounded in the stellar atmospheres. Helium also proliferated, but hydrogen appeared to be about a million times more plentiful in the stars than on Earth. The profusion of hydrogen and helium made all other stellar components appear mere traces.
