THE VERNAL EQUINOX
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About the Astronomical Photographic Data Archive
Photographic plates were the primary data recording medium for generations of astronomers, spanning over 130 years. The data is precious, and we cannot go back in time to image the sky as it appeared to generations of astronomers. A danger exists today for the safety of these plates, estimated at over 2 million. Observatories and universities are space limited and some seek a safe home for the legacy left by so many astronomers. PARI provides space, infrastructure, and Internet access. The goal is to make the archive a resource harnessed by present and generations of astronomers. We look forward to serving the astronomical community as a vital archival resource for future research projects.
Photographic plates were the primary data recording medium in astronomy from the late 1800's until the the 1980's. It is estimated that over two million of these plates exist in observatories and universities around the world.
Many of these observational records are still important as they provide the only way to study the long-term changes of astronomically interesting objects.
Sadly, astronomy's 130-year record of the sky is in
danger of being lost forever. The lack
of a systematic process for preserving astronomical photographs is increasingly
leading to these irreplaceable observations being discarded. The International Astronomical Union passed a
resolution in 2001 that observatories should make efforts to preserve plates,
but most institutions find it hard to justify an investment of staff time or
space for keeping them when they are now infrequently used. At the same time, the astronomers most
familiar with the value of this material are now retiring. In a number of recent cases photograph
collections have simply been tossed out.
PARI has established the North American Astronomical Photographic Plate Preservation & Digitization Center (Plate Center) as a means to preserve this valuable astronomical record. The Plate Center is intended as a national archive for astronomical plates. PARI provides climate controlled storage space and facilities for examining and measuring plates. About 3000 plates have already been received. On-line catalogues and, evenually, scans of the plates will be made available. A logical extension is to include the historic photographic material in the Virtual Observatory, a major astronomical initiative to establish on-line links to a large number of data-bases of observations.
Scientific Reasons for Preserving Plates
There are a number of fundamental scientific reasons for needing access to astronomy's past observations. Basically, all astronomical objects are changing, but often only very slowly. Detecting and understanding these changes offers insight into the nature of the objects. Some questions can only be answered by studying historical data.
As one example, astronomers are presently puzzled by the behavior of Polaris. This well-known object not only changes the amount of small variations in its output, but modern observations compared to ancient ones suggest the star is slowly getting brighter. Another example would be learning the conditions of a supernova or and nova before it erupted.
Studies of historic photographic material have
often produced compelling, often definitive, data to assist the interpretation
of astrophysical phenomena. Table 1, based on astronomy literature, illustrates
the variety and scope of such researches. Click to see the table. The use of the older photographic material seems to be
growing. This can probably be attributed
to a rising awareness of the potential of plate archives. Easier availability of these observations
would surely increase their use.
ScanIt: The IAU Working Group for the Preservation and Digization of Photographic Plates Newsletter, Editor: E. Griffin (DAO)