Digitizing the Stars: Harvard University’s Glass Plate Collection

by Shana Scott

When our team of experts at Anderson Archival isn’t busy with our own historical collection preservation projects, we like to dive into researching other preservation and digitization undertakings. We usually dedicate ourselves to the intimate collections of individuals or private institutions, so we relish opportunities to investigate projects like Harvard University’s Glass Plate Collection.

For most of the sciences, century-old information would be considered at best a historical curiosity and at worst obsolete. But for the last hundred and forty years, Harvard College’s Observatory has housed one of the most comprehensive collections of photographs of the night’s sky as seen from planet Earth, and this data is more than priceless—it’s breakable. For nearly a decade, Harvard has been working to not only protect the historical collection but to bring it—and its enormous amount of underutilized data—into the digital age.

Star Gazing in Glass

Before computers and cameras, the only way to see the stars was to look up with the naked eye or through a telescope. With the advent of the camera, a whole new way to study the stars was born, but taking photographs of the heavens isn’t as easy as pointing and clicking. Photographs taken by telescopes were produced on 8″x10″ or 8″x14″ glass plates coated in a silver emulsion exposed over a period of time. This created a photographic negative on the glass that could be studied during the day.

(DASCH Portion of Plate b41215) Halley’s comet taken on April 21, 1910 from Arequipa, Peru.

This allowed a far more thorough study of the stars than one night of stargazing could offer. By adjusting the telescopes used and exposure times, stars too faint for the human eye to see could be recorded and analyzed. It was Henry Draper who took this technology to the next level.

In 1842, amateur astronomer Dr. Henry Draper used a prism over the glass plate to record the stellar spectrum of stars and was the first to successfully record a star’s spectrum. Dr. Draper and his wife, Anna, intended to devote his retirement to the study of stellar spectroscopy, but he died before they could begin. To continue her husband’s work, Anna Draper donated much of her fortune and Dr. Draper’s equipment to the Harvard Observatory for the study of stellar spectroscopy. Harvard had already begun photographing on glass plates, but with Anna Draper’s continual contributions, Harvard expanded its efforts, photographing both the stars and their spectrums.

Harvard now houses over 500,000 glass plates of both the northern and southern hemispheres, starting in 1882 and ending in 1992 when digital methods outpaced traditional photography. This collection of nightly recordings, which began as the Henry Draper Memorial, has been the basis for many of astronomy’s advancements in understanding the universe.

The Women of Harvard’s Observatory

Edward C. Pickering was the director of the Harvard Observatory when the Henry Draper Memorial was formed, but he did more than merely advance the field through photographing of the stars. He fostered the education and professional study of some of astronomy’s most influential members—women who, at that time, might never have received the chance—or credit—Pickering provided.

Instead of hiring men to study the plates during the day, Pickering hired women. He felt they were more detailed, patient, and, he admitted, cheaper. Williamina Fleming was one of those female computers.  She developed the Henry Draper Catalogue of Stellar Spectra and is credited with being the first to see the Horsehead nebula through her work examining the plates.

The Horsehead nebula taken by the Hubble Space Telescope in infrared light in 2013.
Image Credit: NASA/ESA/Hubble Heritage Team
(DASCH Portion of Plate b2312) The collection’s first image of the Horsehead Nebula taken on February 7, 1888 from Cambridge.

 

 

 

 

 

 

 

 

 

The Draper Catalogue included the first classification of stars based on stellar spectra, as created by Fleming. Later, this classification system would be modified by another notable female astronomer at Harvard, Annie Jump Cannon. Cannon’s classification and organizational scheme became the official method of cataloguing stars by the International Solar Union in 1910, and it continues to be used today.

Another notable female computer was Henrietta Swan Leavitt, who figured out a way to judge the distance of stars based on the brightness of stars in the Small Megellanic Cloud. Leavitt’s Law is still used to determine astronomical distances. The Glass Universe by Dava Sobel chronicles the stories of many of the female computers and the creation of Harvard Observatory’s plate collection.

Digital Access to a Sky Century @ Harvard (DASCH)

The Harvard Plate Collection is one of the most comprehensive records of the night’s sky, but less than one percent of it has been studied. For all of the great work done by the Harvard women and the astronomers who followed them, the fragility of the glass plates meant someone had to travel to Harvard to see them, and then the study of even a single star over a hundred years required a great deal of time. For every discovery made from the plate collection, like finding Pluto, hundreds or thousands more are waiting to be found.

(DASCH Single scan tile from Plate mc24889) First discovery image of Pluto with Clyde Tombaugh’s notes written on the plate. Taken at Cambridge on April 23, 1930.
Initial enhanced color image of Pluto released in July 2015 during New Horizon’s flyby.
Source: NASA/JHUAPL/SwRI
This is a more accurate image of the natural colors of Pluto as the human eye would see it. Taken by New Horizons in July 2015.
Source: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/Alex Parker

 

 

 

 

 

 

 

 

 

With all of this unused, breakable data and advances in computing ability, Professor Jonathan Grindlay began organizing and funding DASCH in 2003 in an effort to digitize the entire hundred-year plate historical document collection. But Grindlay had an extra obstacle to overcome. Many of the plates had handwritten notes written by the female computers and other astronomers. Grindlay had to balance the historical significance of the collection with the vast data it offered. To do this, the plates are scanned at low resolution with the marks in place, then they are cleaned and rescanned at the extremely high resolution necessary for data recording.

A custom scanner had to be designed and constructed specifically for the glass plates and new software was created to bring the digitized image into line with current astronomical data methods. The project hasn’t been without its setbacks, either. Finding funding for the project is a constant problem, and in January 2016, the Observatory’s lowest level flooded. Around 61,000 glass plates were submerged and had to be frozen immediately to prevent mold from damaging the negatives. While the plates are intact, many still need to be unfrozen and restored before being scanned. The custom scanner also had to be replaced because of the flooding.

George Champine Logbook Archive

In conjunction with the plate scanning, a second project is necessary to make the plates useable for extended study. The original logbooks of the female computers contain more than their observations of the plates. These books record the time, date, telescope, emulsion type, and a host of other identifying information necessary to place and digitally extrapolate the stars on the plates. Over 800 logbooks (nearly 80,000 images in total) were photographed by volunteer George Champine.

Those images are now in the time-consuming process of being manually transcribed. Harvard Observatory partnered with the Smithsonian Institution to enlist volunteers who work every day reading and transcribing the vital information in these logbooks. Without this data, the software can’t accurately use the star data scanned from the plates.

Despite all the challenges and setbacks, 314,797 plates have been scanned as of December 2018. The data released and analyzed from the DASCH project has already made new discoveries about variable stars. Once the entire collection of historical documents is digitized, more than a hundred years will be added to the digital collection of astronomical data, and they will be free for anyone to access and study, professional or amateur.

The Harvard Plate Collection is a great example of an extraordinary resource to its community being underused due to the medium. Digital conversion of data is a great way to help any field of research. While Harvard’s plate digitization project provides a model for the conversion of complex data into digital form, not all institutions have the resources to attempt such a large enterprise. If you have a collection in need of digitization, contact Anderson Archival today at 314.259.1900 or email us at info@andersonarchival.com.


Shana Scott is a Digital Archivist and Content Specialist with Anderson Archival, and has been digitally preserving historical materials for over three years. She is involved in every level of the archiving process, creating collections that are relevant, accessible, and impactful. Scott has an MA in Professional Writing and Publishing from Southeast Missouri State University and is a member of SFWA.