Lots of tiny dots with no apparent pattern: Where laypeople can only see milky gray photographs sprinkled with what appear to be random crumbs, it’s enough to make astronomers’ hearts skip a beat. We are talking about historical photographic plates showing the negatives of the night sky.
Together with the Leibniz Institute for Astrophysics Potsdam and the universities of Hamburg and Tartu (Estonia), researchers from the Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) digitized the images and published them online. After ten years, the project was completed.
Although the oldest image is only 129 years old, at a glance compared to the timescales usually associated with astronomy, they have great historical value. They are a treasure trove for academic purposes. Images like these are the only way astronomers can now watch stars move or change in intensity over several decades. They can be used to answer new research questions and take a closer and more objective view of millions of stars.
Since 2012, the research team has been working on digitizing images from the archives of its partner institutes from 1893 to 1998 in the APPLAUSE database – which stands for Archives of Photographic Plates for Astronomical USE – and cataloging them with image details such as date, part of the sky and where the images were taken. In addition, the research consortium has developed software that uses artificial intelligence to remove plate errors caused by scratches or dust and to calibrate the images, allowing them to be compared for scientific purposes for the first time. Researchers worldwide now have access to 4.5 billion measurements of skylight sources for their research.
Over 94,000 digitized photographic plates
A large share of the total 94,090 plates comprises 40,000 photographic plates from the Observatory of Dr. Karla Remeise Bamberg, Institute of Astronomy FAU. These include photographs taken by French researchers between 1963 and 1976 at observatories in the southern hemisphere. These unique images show the southern sky and are the only of their kind available anywhere in the world, as no other astronomy project has documented this part of the sky during this period. As the last images were published four years ago, photographic plates taken in Bamberg between 1912 and 1968 showing the northern sky have now been added to the project. These 17,600 images are the most important addition to what is now the latest data update.
But that’s not all: the project came to the attention of other observatories during an academic conference in Bamberg – for example, the Thüringer Landessternwarte Tautenburg. She gave the research team access to the Karl Schwarzschild Observatory’s archive, the former GDR Academy of Sciences observatory, between 1960 and 1998. Scientists from the Vatican Astronomical Observatory in Castel Gandolfo also showed interest by including their archive in the database and making it available to the global scientific community.