Has their brightness or position in the sky changed? To study stars over longer periods of time, astronomers can now browse through 94,000 images of the sky that are up to 129 years old: The web archive “APPLAUSE”, based on the digitization and processing of archived photo plates from various institutions, is now available completely online. The research team reports that the database has already shown its scientific potential using the example of the unusual star “HD49798”.
They appear inconspicuous, white-grey and somehow dirty, but what they show is heavenly: Up until the age of digital photography, observatories produced photographic plates that showed the starry sky as a negative. Thousands of them are stored in the archives – the oldest specimens date from the pioneering days of modern astronomy. These images of the starry sky are not only interesting from a historical point of view – they have scientific potential. Because they can document stellar changes over several decades and thus provide important insights into the mysteries of the stars. But for modern astronomy, which is based on digital data processing, the information from the photographic plates is difficult to access.
Archive treasures prepared for astronomy
In order to change this, a research team launched the Archives of Photographic Plates for Astronomical USE project, or “APPLAUSE” for short, in 2012: in several steps, the scientists digitized the recordings from the archives of various partner institutes from the years 1893 to 1998. They were then cataloged with recording details such as date, sky section and location. Above all, APPLAUSE can show that a certain recording actually exists and make it accessible to interested parties online. As the Friedrich-Alexander-University Erlangen-Nuremberg (FAU) reports, the project has now been completed after important additional additions and has grown into an enormous treasure trove for astronomy: a total of more than 94,000 photo plates from observatories in Germany, Estonia and the Vatican have now been digitized .
And that means more than just photographing: The research network has developed software that uses artificial intelligence to eliminate errors on the plates such as scratches or dust and to calibrate the recordings and assign them to celestial coordinates. The scientists explain that it is only through this processing that the information becomes scientifically comparable. In addition, the team manually transcribed some existing observation notes and logbooks and recorded them digitally. Thanks to this information, the historical data can be used for scientific studies and, for example, environmental parameters such as temperature and observation quality can be included in the data evaluation. In addition, the scans of the observation logs illustrate the former astronomical working methods and are therefore also of interest to historians.
Which can be reflected in the recordings
But what exactly can astronomers see in the historical photographic plates? As the FAU reports, this becomes clear with a specific example: on photo plates of Dr. Karl Remeis Observatory Bamberg, the star “HD49798” was imaged several times in the 1960s and early 1970s. Only now, thanks to the evaluation possibilities of APPLAUSE, did it become clear that its luminosity was changing: it shows that the star shone brighter and brighter in the years 1964/65, only to shimmer weaker again until 1974. In addition, there were rapid changes in light within a few days.
The long-term information from the photo plate data could thus supplement indications from satellite measurements, according to which X-rays emanate from HD49798. It is now becoming increasingly clear that this signal originates from an invisible, very compact companion of the star – possibly a neutron star. This suspected star duo is considered unique, writes the FAU, because no other constellation of this type has been discovered in space to date.
The research team hopes that their now-completed database can provide the international astronomical community with many more insights into the mysteries of the Universe in the years to come. The scientists who once created the photo plates would certainly be happy about their lasting contribution to research.
Source: Friedrich Alexander University of Erlangen-Nuremberg