Mysterious Light Flashes in Historical Astronomical Observations

• Beatriz Villarroel (Stockholm University)

Room: Lecture Theatre in this talk, I will present results from the VASCO (Vanishing & Appearing Sources during a Century of Observations) project, a large-scale investigation of short-lived optical flashes (transients) detected on historical astronomical photographic plates from the pre-space-age era. By systematically analyzing more than 100,000 transient events recorded on archival sky surveys from the mid-20th century, and combining archival techniques with statistical methods, the project reveals that a subset of these light flashes exhibits non-random patterns that cannot be readily explained by known astronomical sources, instrumental artifacts, or atmospheric effects. We see a deficit of these flashes in the Earth's Shadow. We also find statistically significant temporal correlations with unidentified aerial events as well as nuclear bomb tests. Particular emphasis is placed on correlations with Earth’s shadow geometry, temporal clustering, and historical contextual data, demonstrating how overlooked information embedded in archival material can constrain the physical origin of transient phenomena near Earth. The results highlight the scientific value of revisiting legacy datasets with modern analytical tools and illustrate how historical observations can still challenge current assumptions in astronomy and space science. I will also present and address the current critique to our critique. The presentation discusses the broader implications of these findings for the study of unexplained transient phenomena and argues for the continued integration of archival astronomy into contemporary research on near-Earth space.