Astronomers have digitized 94,000 photographic plates of the night sky, dating back 129 years

Since the early days of the internet, and even computers more generally, there has been a push to collect all of the world’s information, accumulated over thousands of years, into a digital form so that it can at least theoretically last indefinitely. It also makes this information much more accessible to people who are interested in it. This was the motto of the original Google search engine, and specialists in various historical fields have made slow but steady progress in this area over the past few decades. Today, astronomy has acquired one of its largest amounts of historical data as the Friedrich-Alexander-University of Erlangen-Nuremberg has digitized 40,000 of its historical astronomical plates, as well as 54,090 plates from other sources.

The oldest of these plaques dates back 129 years. Although this may not seem like much in astronomical terms, data contained even a “short” time back is valuable for observing the variability of certain stars.

For example, the star HD49798 varied wildly in the 1960s and 1970s. But no one was able to easily quantify by how much and when until the plates were digitally downloaded. Combined with satellite images taken in the late 1990s, scientists now believe that a companion neutron star was the source of this variability, and the variability observed in the plates seems to confirm this idea.

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A plate from 1903 that shows a new supernova.
A plate from 1903 that shows an unknown supernova when this plate was rediscovered.
Credit – W. Cerny / Yerkes Plate Scanning Team

Not only do the plates provide valuable historical snapshots of particularly interesting stars, they also provide insight into regions of the sky that had not yet been digitized for a period of time. For example, a series of plates were taken in the southern hemisphere between 1963 and 1976. They were released a few years ago as part of the ongoing upload process and look like the other digitized examples of the sky in the southern hemisphere for this period. Of the history.

Additional software improvements solved some issues on the plates themselves, such as scratches or smudges. While the underlying data may have been lost, it is at least “fixed” to such an extent that it won’t necessarily screw up the algorithms running on the dataset.

This is not the only effort to collect old astronomical plates, as we have already reported. Digital Access to the Century of the Sky at Harvard (DASCH) is one of the largest, along with the currently completed Photographic Plate Archive for Astronomical Use (APPLAUSE) project. In total, about 400,000 plates have been digitized to date, and researchers are constantly looking for more and developing better techniques to analyze them.

Another 1903 plate of the Andromeda Galaxy, then known as the Andromeda Nebula.
Another 1903 plate of the Andromeda Galaxy, then known as the Andromeda Nebula.
Credit – W. Cerny / Yerkes Plate Scanning Team

Potentially, there could be an end in sight for such projects when all known historical astronomical plates have been uploaded to the internet. But for now, there are undoubtedly more that haven’t been, although the APPLAUSE team has recently received requests from the Vatican Observatory and the Karl Schwarzschild Observatory, which served as a primary observatory for the German Democratic Republic during its time as a Soviet satellite.

With more plates comes more information and the chance of a new discovery being in sight. Astronomers are well known for their collaboration, and projects like APPLAUSE are prime examples of how well it can work. Eventually, it could achieve the end goal of having all pre-internet astronomy data collected and viewable by future generations in their profession.

Learn more:
FAU – Web archive with astronomical photographic plates goes online
UT – Inexpensive approach to digitizing historic glass plates yields astronomical surprise
UT – Calling all volunteers to help digitize astronomical history
UT – Using 19th century technology to time travel to the stars

Main picture:
Negative plate of the Chameleon constellation in the southern hemisphere.
Credit – Dr. Karl-Remeis-Sternwarte Bamberg

Michael E. Marquez