Starlight Detectives

by Alan Hirshfeld

  Despite decades of experiments by George Bond, Warren De La Rue, Lewis Rutherfurd, Benjamin Gould, and David Gill, among others, affirming the absolute stability of photographic emulsions, it was decided that each plate would bear a photoprinted coordinate grid, which would shrink or expand in synchrony with the star images. Such measures were still insufficient to mollify critics who questioned whether stellar positions determined by multiple instruments and observers could be reliably knitted together. Other issues as fundamental as the chemical development of plates, exposure of the coordinate grid, and measurement of stellar brightness were not settled at the Congress (in the last instance, until decades afterward).

  Swept up in a shared scientific–technological euphoria, eighteen observatories in Argentina, Australia, Brazil, Chile, England, France, Germany, Italy, Mexico, Russia, South Africa, and Spain agreed to participate in the massive mapmaking effort. Asked how long the project might take, Mouchez declared that six to ten years would bring the Carte du Ciel to completion. Gill estimated twenty-five years for the Astrographic Catalogue alone, at an annual cost of £10,000. Having neither the inclination nor the resources to pursue such a labor- and money-intensive collaboration, not a single American observatory signed on. Their research was already trending toward the astrophysical: solar studies, photometry, spectroscopy. As Edward S. Holden, director of the Lick Observatory in California, put it, “We should hardly be willing to bind ourselves to a programme which exacted so much routine work for so long.”

  In a further transatlantic affront, Harvard’s Edward C. Pickering secured a $50,000 bequest in 1889 to build a twenty-four-inch photographic telescope in what the English journal The Observatory called a “rival scheme” to make his own celestial map. Its editors, Andrew Common and Greenwich astronomer Herbert Hall Turner, were particularly incensed that Pickering had made no mention of the Astrographic Congress in his 1888 campaign for support:

  . . . thus neither treated the resolutions with the respect to which they are entitled, nor put the case before the public in a fair manner. . . . Should any evil-disposed person or persons charge Prof. Pickering, in thought, word, or deed, with deliberately excluding such mention of the Conference from his appeal as likely to be prejudicial to his chances of success, we cannot acquit him of having materially contributed to this result. . . . He has tacitly condemned the work of the International Conference before it is commenced, and claimed success for himself.

  Pickering warned his benefactor, Catherine Wolfe Bruce, of the brewing storm, adding, “It is the first time I have ever felt obliged to apologize on account of the expected excellence of a piece of work.” Bruce’s response was reassuring, if eccentric: “[W]hatever can be done to promote the work of that Pickering telescope will be clear gain. You know you have entire and undisputed control over that chunky Photo-Sterescope-Telescope.”

  The strong-willed Pickering never shied from controversy: he had only recently concluded a squabble with William Huggins over the wavelengths of spectral lines. (Modern reassessment of the data shows that both men were wrong.) Pickering’s reply to the Observatory editorial is quietly defiant. He defends his fund-raising, as well as his science, point by point, citing his published intention to map the sky in the Observatory’s own pages in 1883. Nor does he see any scientific rationale against duplication of research with instruments of different optical designs. “It is difficult to believe,” he concludes generously, “that the editors of the ‘Observatory’ intend their implication with regard to the work of the Bruce telescope in anything but a friendly spirit, or that they wish to discourage an experiment whose success can be determined only by trial.”

  Edward C. Pickering.

  David Gill wrote sympathetically to Pickering on November 4, 1889: “I am disgusted with the miserable, carping, envious attack made upon you in the ‘Observatory’ article . . . and still more so with its outrageous discourtesy and unscientific spirit. Your quite dignified article in reply I much admire.” A year earlier, Gill and Mouchez had had their own heated exchange with the editors of The Observatory, who claimed that the Astrographic Congress had officially sanctioned only the idea of a star catalog, not its actual production. “[S]uch protests,” Gill scolded, “may be couched in language less contemptuous and more conducive to good feeling amongst astronomers than that which you have employed. . . . I dispute the facts of the explanation, believing them to rest upon a misunderstanding, on your part, of what really took place at the Congress.”

  Each side stuck fast to its own interpretation of what had been agreed to at the Congress of 1887. That David Gill was an evangelist for celestial photography in general and for the Astrographic Catalogue in particular is certain. That he sped the development of the Catalogue faster than more conservative astronomers wished is probably true as well. A colleague remarked that Gill “had the consciousness of a power in him to accomplish great things. He felt that this gave him the right to demand all possible assistance to that end. And he was full of the indomitable energy which compelled support to his projects.”

  Against this contentious backdrop, and with a host of technical matters unresolved, the epic mapping project began. As the plates accumulated, the conversion of these chemical images into hard data proved troublesome. The stellar positions published by some institutions were afflicted with the sort of systematic errors the skeptics had foreseen. The Congress had tabled the issue of photometry—stellar brightness measurement—anticipating research that would define the relationships between length of exposure, size or opacity of a star’s image, and the actual magnitude number astronomers use to quantify a star’s brightness. These studies took far longer than anticipated. (In an ironic turnabout, the supervisory committee of the Carte du Ciel would ultimately adopt Edward Pickering’s list of “standard stars” as its photographic brightness gauge. Pickering’s “rival scheme” proved beneficial after all.)

  As years, then decades passed, the financial and scientific burdens of the Carte du Ciel became increasingly oppressive. Participating observatories had saddled themselves with an expensive, laborious, and mundane task that effectively barred them from new avenues of research. Four observatories withdrew, forcing others to take up their assigned zones. Most of the participants were still working on their part of the Astrographic Catalogue well into the twentieth century, with the last remnant completed in 1964. The final product, scattered among 150 printed observatory reports, contains data for 4.6 million stars. By the original agreement, stellar positions are listed as a pair of x and y coordinates, relative to each plate’s center. That is, an astronomer cannot simply look up the celestial latitude and longitude of a star, but has to compute them from a mathematical formula: a galling task during the pre-calculator, precomputer age. Until recently, little use was made of the data.

  Nuns measuring star positions on Carte du Ciel plates at the Vatican Observatory around 1920.

  The Carte du Ciel fared worse than its catalog counterpart: only half of the plates for the great star map were ever exposed, and of these, just a small fraction actually engraved and printed. Meanwhile, twentieth-century technology overran the restrictive instruments and methods adopted for the Carte du Ciel. By 1916, astronomer Frank Schlesinger, at the Yerkes Observatory outside Chicago, was photo-mapping with a telescope whose field of view was six times the area of a Carte du Ciel plate. The larger plates captured a greater number of well-observed reference stars, against which the positions of others are gauged.

  As the Carte du Ciel lumbered into the twentieth century, observatories in the United States pursued privately funded programs of astrophysical research and telescope building that arguably brought them to world dominance in these areas. In 1895, Edward Pickering articulated the American viewpoint as the explicit “advancement of the physical side of astronomy. While precise measures of position have not been neglected, the policy has been rather to undertake such studies of the physical properties of stars as would not be likely to be made at other
observatories.”

  The Carte du Ciel proved that old astronomy plus new technology does not necessarily equate to new astronomy. Its hard-won photographic charts yielded no major discoveries and no insight into the physics of the stars themselves. Nor did the plethora of positional data leverage early twentieth-century science into more productive directions. (Tycho Brahe’s sixteenth-century planetary observations—superficially, a pointless heap of numbers—allowed Johannes Kepler to derive the laws of orbital motion.)

  Whereas traditional exact astronomers were, at base, mathematicians with a telescope (and now maybe a camera), the upcoming generation of scientists had scant interest in adding the nth decimal place to a star’s position. Celestial cartographers viewed stars as luminous markers on a coordinate grid, while proponents of the so-called New Astronomy envisioned stars as distant suns, whose mass, chemical composition, energy sources, even life histories, might be divined through nascent technology. These astrophysicists were convinced that cosmic light held clues to the physical state of stars and nebulae. Their objective was the development of instruments, methods, and theories to best capture and interpret a celestial body’s emissions.

  Already by 1887, Princeton astronomer Charles A. Young ventured that “inquiries of this [physical] sort receive to-day fully as great an expenditure of labor, time, and thought as the older work of position-observation, and they are pursued with even a heartier zest.” As headline-making astrophysics gradually displaced the more sedate classical astronomy, the Carte du Ciel receded in significance. What began as a grand boulevard to the glorification of positional astronomy narrowed over the decades into a patchwork path to the scientific hinterlands.

  Despite its manifest failure as a wellspring of scientific progress, the Carte du Ciel did elevate celestial photography in the minds of professional astronomers. The institutional attention legitimized its use and made its perfection through experimentation an acceptable end in itself. Meetings of the Carte du Ciel committees swelled into educational forums in emerging methods and gave rise, in 1919, to today’s International Astronomical Union. Even for positional astronomers, with their long tradition of visual observation, there was no turning back. The 1890s became an interregnum between the reign of the eye and that of the camera: twentieth-century astronomical research would be photographic.

  By 1996, the entire Astrographic Catalogue had been keyboarded—in an earlier phase, keypunched—into the computer. This made possible a series of statistical analyses and wholesale corrections of the data, including many typographical errors. (The new Astrographic Catalogue is accessible at the website of the U.S. Naval Observatory.) The restructured database has allowed astronomers to measure with great precision the movements of stars since the turn of the previous century. Thus, to a modest degree, David Gill’s vision for his great celestial map has been achieved. Nevertheless, astronomy historian David Evans wonders whether the Carte du Ciel was Gill’s “greatest triumph or his grandest failure.”

  The Carte du Ciel sprang from the unexpected appearance of stars in a photograph of a comet. From this, astronomers were inspired to use the camera as an accessory for celestial measurement. But the close of the nineteenth century also highlighted the camera’s potential as an agent of discovery. In March 1887, during a long-term project to photograph and classify stellar spectra, Edward Pickering found that the most prominent spectral line of the star Mizar was, in fact, a double-line. The source of the spectrum, Pickering surmised, is not a single star, but a pair of stars—a binary system—so close together that they appear as a unitary disk in the telescope. Only through a photographic time exposure could this subtle spectral anomaly have been detected. A second spectroscopic binary was found two years later by Pickering’s assistant Antonia Maury, niece of Henry Draper and one of Harvard’s first woman astronomers.

  On December 22, 1891, Maximilian Wolf, at the University of Heidelberg, noticed a small streak on an otherwise blemish-free picture of a star field. The streak, he realized, was an unknown asteroid, its orbital movement having traced out a stubby hairline on the time-exposed plate. Within two years, Wolf had photographed eighteen more asteroids, and during his lifetime 228. The original he named Brucia, after his American benefactor, Catherine Wolfe Bruce, who also funded Pickering’s work. Other astronomers joined the photographic production line, boosting the languid rate of asteroid discovery beyond the capacity of the mathematicians charged with computing their orbits. (So distressed was one data analyst by the torrent that he dubbed these minor planets the “vermin of the skies.”) And if asteroids were insufficient to motivate astronomers to take up the camera, might not the additional incentive of discovering a trans-Neptunian planet?

  American astronomer Edward Emerson Barnard is credited with the first photographic discovery of a comet in a picture taken October 12, 1892, at Lick Observatory. The camera also revealed deep-space nebulae that had gone undetected by eye. The Orion Nebula and the cirrus-like veil of the Pleiades star cluster were fully delineated only with the advent of dry-plate photography. The famous Horsehead Nebula in Orion was first seen by Williamina Fleming, another of Edward Pickering’s assistants (previously, his housemaid), on a photographic plate from 1888. Two years later, Maximilian Wolf discovered and named the continent-shaped North American Nebula.

  But it was pictures of the controversial spiral nebulae that were to cement the acceptance of photography by professional astronomers. During the 1890s, Isaac Roberts published his glorious album of celestial images, including several spiral nebulae. Simultaneously, Andrew Common’s cast-off three-foot telescope began its new life as a workhorse photographic instrument on a California mountaintop. Here it would harness the exquisite power of the chemical plate to open a new window onto the nature of the universe.

  Chapter 12

  AN UNCIVIL WAR

  It is a remarkable and highly significant fact that most of the nebulae photographed with the Crossley reflector seem to be spirals.

  —James E. Keeler, Lick Observatory, 1899

  TELESCOPES CAN HAVE A LONG LIFE. They might serve their original owner for decades, then fall into the hands of another starry-eyed enthusiast, a school, or a local astronomy club. But rarely has any backyard telescope traveled an ocean to occupy a mountaintop perch at one of the world’s premier research institutions. Andrew Common’s pioneering three-foot reflector, which thrust the photographic Orion Nebula into the public consciousness, made such a journey during the summer of 1895. From its second home, on Edward Crossley’s Yorkshire estate, the telescope and its dome were dismantled—sixty-five-thousand pounds of iron, steel, and wood—and shipped to Lick Observatory on Mount Hamilton in California.

  Lick Observatory on Mount Hamilton, California, in the 1890s.

  The Crossley telescope was to be a working monument to its donor’s generosity (which awoke only after Lick refused to meet Crossley’s asking price). Although reflectors were still considered inferior to refractors, the largest-in-the-nation Crossley reflector was portrayed as a worthy complement to Lick’s largest-in-the-world refractor, also three feet across. In appearance, there was no charitable comparison: the stubby Crossley was a bulldog, its long-tubed counterpart a greyhound. Yet the age of the large refractor was coming to an end; graceless as it was, the Crossley telescope represented the future of astronomical observing.

  When James E. Keeler took up the directorship of the Lick Observatory in 1898, he walked into a civil war. On one side stood Edward S. Holden, Keeler’s controversial predecessor, an energetic administrator and fund raiser, but at best, a mediocre research scientist. In his decade-long tenure, Holden had managed to alienate most of the observatory’s staff, who variously referred to him as “the Dictator,” “Prince Holden,” or “that contemptible brute.” On the other side of the conflict stood the ambitious William J. Hussey, lured to Lick from Stanford University with expectations, if not promises, of a fast-track to professional prominence. Hussey’s unspoken goal—and the source
of a desperate urgency—was to return to Stanford with funding for a world-class observatory.

  And in the middle of this high-flown battlefield, an objective fought over but unwanted was Crossley’s telescope. With proper restoration, Holden believed, the Crossley might become one of the premier photographic instruments in the world. Unlike the lens of a refractor, a mirror does not absorb the energetic violet rays that stimulated nineteenth-century photographic emulsions. Secondly, although their apertures were identical, the Crossley’s compact form (technically, its fast focal ratio) was more favorable to photography than the stringbean shape of Lick’s big refractor. Nor does a reflector suffer from chromatic aberration, which causes some refractors to cast rainbow fringes around celestial images. Nevertheless, Holden had no intention of tackling the project himself. Instead, he ordered his new recruit Hussey to bring the Crossley into operation.

  Hussey was shocked: he had expected to continue Edward Barnard’s photographic survey of the Milky Way (Barnard resigned in 1895 over tensions with Holden), or perhaps even carry out observations with Lick’s vaunted refractor. Hussey took one look at the homely reflector from England and pronounced it “a pile of junk.” In its idiosyncratic mount—“as antiquated . . . as Noah’s ark”—he saw only a fifteen-thousand-pound impediment to his career plans. In fact, the narratives of innovators like Henry Draper, Andrew Common, and Isaac Roberts did portray reflectors as a mechanic’s telescope, in frequent need of manual corrections, optical alignment, and resilvering. Hussey’s antipathy toward the Crossley was founded in the experiences of others, as well as in the mount’s documented inadequacies. C. Donald Shane, Lick’s director from 1945 to 1958, admitted that the original mount of the Crossley reflector was “. . . a monstrosity. Despite the elaborate system of platforms and ladders, it was almost impossible at times to reach the eyepiece. One observer suggested that the dome be filled with water so the astronomers could observe from a boat.”