Old, digitized astronomical images taken before the human spacefaring age offer a rare glimpse of the sky before the era of artificial satellites. In this paper, we present the first optical searches for artificial objects with high specular reflections near the Earth. We follow the method proposed in Villarroel et al. (2022) and use a transient sample drawn from (Solano et al. 2022). We use images from the First Palomar Sky Survey to search for multiple (within a plate exposure) transients that, in addition to being point-like, are aligned along a narrow band. We provide a shortlist of the most promising candidates, including one with ∼3.9σ statistical significance. As in previous cases (Villarroel et al. 2021, Solano et al. 2023), no known astrophysical or instrumental explanations fully account for these events. We explore remaining possibilities, including fast reflections from highly reflective objects in geosynchronous orbit, or emissions from artificial sources high above Earth's atmosphere. Notably, the ∼3.9σ candidate coincides in time with the Washington D.C. 1952 UFO flyover, and another (a ∼2.0σ candidate) falls within a day of the peak of the 1954 UFO wave (Figuet 1980). We also find a highly significant (∼22σ) deficit of transients from Solano et al. 2022 within Earth's shadow, supporting the interpretation that sunlight reflection plays a key role in producing these events. This study should be viewed as an initial exploration into the potential of archival photographic surveys to reveal transient phenomena, and we hope it motivates more systematic searches across historical datasets.
King-Aaron•6mo ago
Old, digitized astronomical images taken before the human spacefaring age offer a rare glimpse of the sky before the era of artificial satellites. In this paper, we present the first optical searches for artificial objects with high specular reflections near the Earth. We follow the method proposed in Villarroel et al. (2022) and use a transient sample drawn from (Solano et al. 2022). We use images from the First Palomar Sky Survey to search for multiple (within a plate exposure) transients that, in addition to being point-like, are aligned along a narrow band. We provide a shortlist of the most promising candidates, including one with ∼3.9σ statistical significance. As in previous cases (Villarroel et al. 2021, Solano et al. 2023), no known astrophysical or instrumental explanations fully account for these events. We explore remaining possibilities, including fast reflections from highly reflective objects in geosynchronous orbit, or emissions from artificial sources high above Earth's atmosphere. Notably, the ∼3.9σ candidate coincides in time with the Washington D.C. 1952 UFO flyover, and another (a ∼2.0σ candidate) falls within a day of the peak of the 1954 UFO wave (Figuet 1980). We also find a highly significant (∼22σ) deficit of transients from Solano et al. 2022 within Earth's shadow, supporting the interpretation that sunlight reflection plays a key role in producing these events. This study should be viewed as an initial exploration into the potential of archival photographic surveys to reveal transient phenomena, and we hope it motivates more systematic searches across historical datasets.