More than 220,000 fragile glass plates of yesteryear's night sky are being preserved forever in digital form.

Eta Carina Nebula

This negative image of the Eta Carinae Nebula taken in 1968 with the CTIO 0.9-m Curtis-Schmidt telescope is one of thousands being scanned to digital media. Even in this low-resolution scan, the nebula reveals elegant details.

PARI Astronomical Photographic Data Archive

Long before the invention of digital cameras, astronomers spent millions of telescope hours photographing the night sky — they measured star brightnesses, detected comets and planets, mapped our galaxy, and built the foundations of our understanding of the universe.

Now all of this raw beauty is held on thin, fragile pieces of glass, which stores the photometric, astrometric, spectral and surface brightness data for posterity. Like other preservation projects, the Astronomical Photographic Data Archive (APDA) has set about archiving and digitizing its glass photographic plates to forever safeguard their hundreds of terabytes of data. This astronomical legacy will give today’s explorers a time machine to the night sky of the past.

APDA was established in 2007 as a center for collecting, restoring, preserving and storing astronomical photographic data. The archive is housed on the campus of the Pisgah Astronomical Research Institute (PARI), located at a former NASA tracking station in western North Carolina (S&T: September 2013, page 36). The APDA archive contains about 20% of all the plates in North America, including at least 40 plate collections. Smaller institutions and individuals send more plates every year.

From studies of the Magellanic Clouds to asteroid astrometry, the nearly 220,000 plates have already done their part for science. Generations of astronomers have used the photographic plates to identify quasars, make parallax measurements, conduct star surveys, study nova evolution, and aid in spectral classification. But each scientist usually only studied a select number of objects per plate, each covering a several-degree field of view. The amount of unexplored photographic data is truly a resource for discovery of discrete and often time-related data.

APDA photo archives

This room is one of four used by the Astronomical Photographic Data Archive project to store its collections of astronomical data.

PARI Astronomical Photographic Data Archive

For example, APDA’s Nova Survey Project involves 42,000 images obtained from the Harvard Photographic Meteor Program conducted from 1951 to 1959. The Meteor Program used two Super-Schmidt 0.31-meter, f/0.85 telescopes, each with effective fields of view of 52 degrees, separated by 80 km in New Mexico. The telescopes were placed in a no-fly zone and before the era of artificial satellites. Now astronomers are sifting through the images, originally created to study meteors, in search of transient events such as stellar explosions. Estimates predict that this photographic data set should contain at least 40 undiscovered novae.

The fragile and analog nature of astronomical photographic plates makes their data difficult to access. To address this, the APDA team is developing the Astronomy Legacy Project (ALP) — bringing the diverse and rich data set of 20th century astronomy into the 21st century digital world. The team is planning on purchasing a very high-precision scanner to digitize collections in the Astronomical Photographic Data Archive (APDA).

And, to support this effort, PARI has launched a crowdfunding program on Kickstarter. The legacy of generations of astronomers will finally be shared with the entire world.

Michael Castelaz is an astronomer and Science Director at the Pisgah Astronomical Research Institute. He received his Ph.D. in astrophysics from the University of Wyoming in 1984, and he is interested in searching astronomical photographic plate collections for singular stellar events like novae.


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