Astronomy

Astronomers Have Digitized 94,000 Photographic Plates of the Night sky, Going 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, built up over thousands of years, into a digital form so it can at least theoretically latest indefinitely. It also makes that information much more accessible to people interested in it. That was the motto of the original Google search engine, and specialists in various historical fields have been making slow but steady progress in doing just that over the past few decades. Now astronomy has gained one of its largest hauls of historical data as the Friedrich-Alexander University of Erlangen-Nuremberg has digitized 40,000 of its historical astronomical plates, along with 54,090 plates from other sources.

The earliest of these plates goes back 129 years. While that does not seem like much in astronomical terms, data contained even that “short” of a time back is valuable for watching the variability in some stars. 

For example, the star HD49798 varied wildly back in the 1960s and 70s. But noone was able to easily quantify by how much and when until the plates were digitally uploaded. Combined with satellite images taken in the late 1990s, scientists now think that a neutron star companion was the cause of this variability, and the variability seen in the plates seems to confirm that idea.

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

Not only do the plates offer valuable historical takes on specifically interesting stars, but they also provide insight into regions of the sky that had not yet been digitized during a certain time period. 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 process of uploading and stand as the other digitized examples of the sky in the southern hemisphere for that period of history.  

Additional software improvements managed to fix some issues on the plates themselves, such as scratches or blotches. While the data underlying them might have been lost, at least they are “corrected” to a point where they won’t necessarily screw up any algorithms run on the data set.

This isn’t the only effort to collect old astronomical plates, as we’ve reported before. The Digital Access to the Sky Century at Harvard (DASCH) is one of the more prominent, as well as the currently completed project of The Archives of Photographic Plates for Astronomical USE (APPLAUSE). In total, there are around 400,000 plates that have been digitized so far, and researchers are constantly searching for more and developing better techniques to analyze them.  

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

Potentially there could be an end in sight for these sorts of projects when all known historical astronomical plates have been uploaded to the internet. But for now, there’s undoubtedly more that haven’t been, though the APPLAUSE team recently received requests from both the Vatican’s observatory and the Karl Schwarzschild Observatory, which served as the main observatory for the German Democratical Republic during its time as a Soviet satellite.

With more plates comes more information and chances that a novel discovery could be in the offing. Astronomers are well known for their collaboration, and projects such as APPLAUSE are perfect examples of how that can work well. Eventually, it might reach the end goal of having all of the pre-internet astronomy data collected and searchable by future generations in their profession.

Learn More:
FAU – Web archive with astronomical photographic plates goes online
UT – Low-Cost Approach to Scanning Historic Glass Plates Yields an Astronomical Surprise
UT – Calling All Volunteers to Help Digitize Astronomical History
UT – Using 19th Century Technology to Time Travel to the Stars

Lead Image:
Negative plate of the Chamaeleon constellation in the southern hemisphere.
Credit – Dr. Karl-Remeis-Sternwarte Bamberg

Andy Tomaswick

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