The Glass Universe

by Dava Sobel

  • • •

  NO ASTRONOMER WORKING TODAY uses glass plates to photograph the cosmos. CCDs, or charge-coupled devices, began replacing photographic film in the 1970s, and for the past two decades virtually all celestial images have been captured and stored digitally. But no matter how broadly or deeply modern sky surveys probe outer space, they cannot see what the heavens looked like on any given date between 1885 and 1992. The record preserved in the Harvard plate collection of one hundred years of starry nights remains unique, invaluable, and irreplaceable.

  The half a million glass plates reside in the expanded Brick Building. They stand on their long edges, leaning slightly to the left or right on the shelves of the many metal cabinets. Some early photographs still wear their original paper jackets, covered over with handwritten commentary from their long-ago keepers. Old or new, each envelope bears an affixed bar-coded sticker containing accession information that helps the current curator maintain order in the plate stacks. Visiting researchers file in and out. Historians prize the plates for their dated information, for the antiquated union of glass and silver-gelatin emulsion that embeds the stars. Astrophysicists consult the plates to enrich and interpret the latest findings through “time domain astronomy.” Celestial denizens undreamed of at the start of Pickering’s sky patrol—pulsars, quasars, black holes, supernovae, X-ray binaries—nevertheless left their marks on the plates.

  When computers were human, they scanned these photographs by eye for as many interesting objects as they could find. There were never enough “readers” to utilize the plate library to Pickering’s or Shapley’s satisfaction. The most motivated of their methodical workers, when confronted with an image containing as many as one hundred thousand stars, could carry discovery only so far. Even now, the information content of the plate stacks is largely untapped.

  To extract all that waiting data with modern computerized algorithms, the Harvard-Smithsonian Center for Astrophysics inaugurated a digitization project in 2005, with funding from the National Science Foundation. The ongoing goal is to clean, scan, and analyze every plate, so as to provide “Digital Access to a Sky Century at Harvard,” or DASC@H. After more than ten years, the work is approximately one-quarter complete.

  All procedures and instruments for DASC@H (pronounced “dash”) have had to be invented and assembled on-site, from the dishwasher-like machine that cleans the plates to the custom-built, high-speed scanner that accommodates the standard 8 × 10 and also the Bruce-size 14 × 17 plates. At each stage of activity, curatorial concerns vie with scientific requirements. For example, the plate-cleaning process, an essential prelude to producing clear, crisp scans, automatically erases any markings jotted on the glass by iconic figures such as Henrietta Leavitt and Annie Cannon. The compromise solution is to photograph each marked photograph before cleaning it—and each jacket, too—to record all those notations. Certain plates are judged too historic to be tampered with, and will be archived indefinitely. One of these holds an image of a star field made while the nature of spiral nebulae still sparked debate. On it, someone circled a tiny swirl of matter too small to see without a magnifying loupe. Next to the inked circle, an inked question arises: Galaxy?

  The index cards and logbooks that list the telescope, sky coordinates, date, and exposure time of each photograph are also coming online, thanks to willing individuals who spend a few hours every day transcribing them via the Smithsonian Institution’s crowdsourcing platform. Citizen scientists work in front of their own computer screens, from high-resolution photographs of each logbook’s hundred pages, each page crammed with statistics and remarks on as many as twenty plates.

  At the outset, DASC@H team members named reasons beyond data mining as justification for their long-term project. They wanted to make the plates available for convenient worldwide use, to protect them from careless handling by interested borrowers, and to save the contents from predictable deterioration, such as emulsion separation. Once the process was under way, an unanticipated event provided further justification for the effort.

  On Monday morning, January 18, 2016, a water main burst under a courtyard at 60 Garden Street, the official address of the CfA. The pipe provided water to four nearby buildings, including the original Brick Building and its 1902 and 1931 extensions. The rupture released water underground with enough force to breach the foundation walls and flood the lower level of the plate vault. Approximately sixty-one thousand plates were submerged. Experts from the on-campus Weissman Preservation Center responded to the emergency and diagnosed mold as the worst-case outcome of immersion. Spores that colonized the plates might configure their own new biological constellations. For all of Pickering’s foresight in initiating and protecting the collection, he never suspected that water, not fire, would threaten its integrity.

  The conservators prescribed the immediate removal of the plates to a dry place where they could be kept below zero degrees Centigrade—too cold for mold to grow. The prevailing weather conditions at the time, clear with temperatures below freezing, turned the outdoors into a temporary safe haven. Dozens of volunteers came to the collection’s aid; they traipsed in and out of the stacks all through Monday night and Tuesday, carrying armloads of fragile plates to dry ground. Not a single piece of glass was broken.

  By Wednesday the rescued plates had been driven in trucks to the Polygon Document Restoration Services in North Andover, where they were vacuum-freeze-dried, to be later thawed out and cleaned, one by one.

  One by one, the way the stars emerge as evening falls, the drowned, muddied plates will revive the vivid skyscapes that impressed them when they were sensitive to light. Once again they will reveal the stellar spectra, the variable stars, the star clusters, the spiral galaxies, and all the other luminous sights they first conveyed to a small but dedicated circle of women.

  Anna Palmer Draper funded the Harvard project to photograph the spectra of the stars—the unfulfilled dream of her late husband. She sat for this portrait by John White Alexander in 1888.

  Dark Fraunhofer lines cutting across the rainbow spectra of the Sun and other stars gave Father Angelo Secchi of the Vatican Observatory a means of categorizing the various stellar types. This image from his 1877 book, Le Stelle: Saggio di Astronomia Siderale, shows examples of the classes he identified.

  The expedition party that gathered in Rawlins, Wyoming Territory, to view the total solar eclipse of July 29, 1878, included (from far right) English astronomer Norman Lockyer, Thomas Edison, and Henry and Anna Draper.

  The dome of the Great Refractor dominated the appearance of the Harvard College Observatory in the 1870s. A smaller telescope was mounted in the west wing.

  Edward Charles Pickering became the director of the observatory in 1877 and served for more than forty years as its visionary leader.

  Williamina Paton Stevens Fleming began working for the Pickerings as a maid, but later went on to establish a system for classifying stars by their spectra.

  Mrs. Fleming (standing at rear) earned a supervisory role over the other female computers and also a coveted Harvard title as curator of astronomical photographs.

  Blue ink squiggles on these paired spectra of the star Mizar reveal a doubled K line in the top image and a single K line in the bottom one—differences that led Edward Pickering to his 1887 discovery of the first spectroscopic binary.

  In order to photograph the stars of the Southern Hemisphere, Harvard established an auxiliary observatory, the Boyden Station, in Arequipa, Peru, within sight of the dormant volcano El Misti. The observer’s house built by William Pickering is at right.

  Annie Jump Cannon, a Wellesley College graduate, was continuing her astronomy studies at Radcliffe and also assisting at the Harvard Observatory when this photograph was taken, ca. 1895.

  Antonia Maury (far right) and her sister Carlotta (far left) are pictured here with their Aunt Ann (Mrs. Daniel Draper) and young cousins Harriet and Dorothy Ca
therine. The woman in the dark dress is unidentified.

  Stars appear as black dots in this negative plate of the Small Magellanic Cloud, a satellite galaxy of the Milky Way that can be seen from the Southern Hemisphere. The splotch at right is the dense globular cluster of stars known as 47 Tucanae.

  Called a fly spanker for its resemblance to a fly swatter, this diminutive instrument helped computers compare the relative brightness of stars.

  Henrietta Swan Leavitt discovered a relation between certain stars’ peak brightness and the time it took them to cycle through their changes in magnitude. This “period-luminosity relation,” also called the Leavitt law, provides a means for measuring distances across space.

  Many noted foreign astronomers joined this Harvard gathering in August 1910. Miss Cannon, in a white dress, is at far left. Leon Campbell kneels just in front of Miss Cannon, and sitting in front of him is Winslow Upton, librettist of The Observatory Pinafore. The woman next to Miss Cannon is Lucy May Russell, wife of Henry Norris Russell, who is at her side. Pickering stands front and center, Mrs. Fleming, wearing all black, also in the front row, and Henrietta Leavitt just behind her, in white. Solon Bailey, bald and bearded, sits at far right.

  Pickering poses at the entrance to the Brick Building with the female staff, ca. 1911. Margaret Harwood is at far left, Arville Walker just in front of her. Ida Woods stands at far right in the front row. The white-haired lady on the step behind her is Florence Cushman. At her right is Annie Cannon, and Evelyn Leland is in the back row between them.

  This two-hour-long exposure of the Large Magellanic Cloud, taken with the 8-inch Bache telescope at Arequipa on January 23, 1897, gave the staff in Cambridge hundreds of objects to number and ponder over a period of years.

  This 1918 chain of Harvard assistants begins with Ida Woods (at far left) and links to Evelyn Leland, Florence Cushman, Grace Brooks, Mary Vann, Henrietta Leavitt, Mollie O’Reilly, Mabel Gill, Alta Carpenter, Annie Cannon, Dorothy Block, Arville Walker, and telescope operator Frank E. Hinkley, ending (at far right) with chief of stellar photography Edward King.

  The Brick Building, where the glass plates were stored, became a second home to Annie Cannon (left), who classified more than a quarter of a million stars by their spectra, and her colleague Henrietta Leavitt, who sought out variable stars and monitored their behavior.

  In a typical work session, Miss Cannon would write numbers next to all the spectra on a plate, then call out each number and also her judgment of its spectral type to a recorder who wrote down her pronouncements.

  Soon after Harlow Shapley took over as director of the observatory, Annie Cannon accompanied Solon and Ruth Bailey to Peru, where she often walked (or rode) for hours during the day and then observed late into the night.

  Miss Cannon said she did not mind climbing up and down ladders to operate the 13-inch Boyden telescope and take her own plates of the southern stars.

  Harlow Shapley enjoyed the flexibility of the unique revolving desk-and-bookcase combination devised by his predecessor, Edward Pickering.

  Cecilia Payne traveled to the Harvard Observatory from Cambridge University in England, where she had been inspired by Arthur Stanley Eddington to devote herself to astronomy.

  Miss Payne (right) and Adelaide Ames (center), called the “Heavenly twins,” welcomed Harvia Hastings Wilson as the third graduate student in 1924. Miss Payne went on to earn a Ph.D.—the first doctoral degree in astronomy awarded at Harvard.

  Margaret Harwood sat on the floor for this posed tableau taken on May 19, 1925. Harvia Wilson is at far left, sharing a table with Annie Cannon (too busy to look up) and Antonia Maury (left foreground). The woman at the drafting table is Cecilia Payne.

  The 1929 New Year’s Eve performance of The Observatory Pinafore featured (from left to right) Peter Millman; Cecilia Payne as Josephine; Henrietta Swope, Mildred Shapley, Helen Sawyer, Sylvia Mussells, and Adelaide Ames as the computer chorus; and Leon Campbell in the role of Professor Searle.

  The switch from tabulated columns of numbers to the chart format lowered the cost of publishing Miss Cannon’s classifications for the Henry Draper Extension.

  Antonia Maury installed a 6-inch Clark telescope at the old Draper homestead in Hastings-on-Hudson. She intended it for the edification of local residents, especially children.

  As youngsters, Katherine and Edward Gaposchkin played in and around the observatory, within easy reach of their parents, Sergei Gaposchkin and Cecilia Payne-Gaposchkin.

  Roughly half a million glass plates tilt to the left and right on shelves inside metal cabinets at the Harvard Plate Stacks. Each plate’s paper jacket identifies the date the photograph was taken, the celestial area covered, the telescope employed, the duration of exposure, the condition of the sky, and other pertinent information.

  The Great Refractor stands idle today inside its large dome. Two people can still sit side by side in the commodious, adjustable observing chair designed by founding director William Cranch Bond, but the skies over Cambridge are no longer dark enough at night to permit new discoveries.

  APPRECIATION

  My warmest thanks to:

  Wendy Freedman, the John & Marion Sullivan University Professor of Astronomy and Astrophysics at the University of Chicago, who planted the idea for this book more than twenty years ago;

  Michael Carlisle of InkWell Management, who helped shape the project and find it an ideal home with Kathryn Court at Viking;

  Alison Doane, Jonathan Grindlay, David Sliski, and Lindsay Smith, for access to the glass universe in the Harvard Plate Stacks;

  Christopher Erdmann, Maria McEachern, Amy Cohen, Louise Rubin, Katie Frey, and Daina Bouquin of the John G. Wolbach Library in the Harvard-Smithsonian Center for Astrophysics, for taking me in as one of their own;

  Robin McElheny, Tim Driscoll, Pamela Hopkins, Robin Carlaw, Barbara Meloni, Ed Copenhagen, Caroline Tanski, Samuel Bauer, Michelle Gachette, and Jennifer Pelose in the Harvard University Archives, for opening Miss Cannon’s diaries and other paper treasures;

  Susan Ware, Sarah Hutcheon, and Jane Kamensky of the Schlesinger Library, for illuminating the Radcliffe backgrounds of numerous Harvard ladies;

  Smith College students, faculty, and staff, for providing the perfect environment in which to write about women’s history;

  William Ashworth, Barbara Becker, David DeVorkin, Suzan Edwards, Owen Gingerich, Alyssa Goodman, Katherine Haramundanis, Doug Offenhartz, Jay and Naomi Pasachoff, William Sheehan, Joseph Tenn, and Barbara Welther, for reading and commenting on early drafts;

  Thomas Fine and Lia Halloran, for help illustrating this story;

  Isaac Klein, Stephen Sobel, Alfonso Triggiani, Barry Gruber, and Gary Reiswig, for their consistent encouragement;

  Sheryl Heller and the crew at GeekHampton in Sag Harbor, New York, for invaluable assistance with the other kind of computers.

  SOURCES

  CHAPTER ONE: Mrs. Draper’s Intent

  The letters between Anna Palmer Draper and Edward Pickering are held in the Harvard University Archives, along with all the other observatory correspondence, and are quoted here with permission.

  Pickering’s call for women assistants in the observation of variable stars was announced in the Statement of Work Done at the Harvard College Observatory During the Years 1877–1882 and was also issued as a separate brochure, “A Plan for Securing Observations of the Variable Stars.”

  Hard copies of all the observatory publications, such as the Annals and the annual reports, are held in the John G. Wolbach Library at the Harvard-Smithsonian Center for Astrophysics in Cambridge. Most of these materials have been digitized and can be read online at http://adsabs.harvard.edu/historical.html.

  CHAPTER TWO: What Miss Maury Saw

  The letters of Antonia Maury to her Draper relatives are held in the Library of Congress and excerpted here with the permission of her
family.

  All correspondence concerning the Boyden Station of the Harvard College Observatory is held in the Harvard University Archives.

  CHAPTER THREE: Miss Bruce’s Largesse

  Letters to Edward Pickering from Catherine Wolfe Bruce, as well as those from her sister Matilda, are held in the Harvard University Archives.

  The article by astronomer Simon Newcomb that galvanized Miss Bruce was titled “The Place of Astronomy Among the Sciences”; it appeared in 1888 in the Sidereal Messenger.

  Williamina Fleming’s prepared speech for the Chicago conference was published as “A Field for Woman’s Work in Astronomy” in 1893 in Astronomy and Astro-Physics.