Palomar Observatory, California: Three point sources on sky survey plate vanish in an hour
A red-sensitive Palomar Observatory Sky Survey plate taken on July 19, 1952, shows three 15th-magnitude point sources in Cygnus that are absent from a blue plate taken less than an hour later.
Background
Three 15th-magnitude point sources within 10 arcseconds of each other were recorded on a red-sensitive image of the Palomar Observatory Sky Survey at RA 21h18m10.4s, DEC +50°22′43.4″ in the constellation Cygnus. They show no peculiar shapes or elongation such as asteroids, meteorites, cosmic rays, plate defects or aircraft might produce. The three sources are absent from all later exposures of the region over the following 71 years, including a Palomar blue-sensitive image taken less than one hour later. Enrique Solano and colleagues described the triple transient in an arXiv paper in October 2023; Avi Loeb suggests the point sources might be cosmic-ray impacts. The account follows the entry in George M. Eberhart's chronology UFOs and Intelligence (CUFOS) and the sources cited there; it is not an independent determination by From Beyond Space.