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A jellyfish-like luminous phenomenon visible across Karelia and parts of Finland was reported by hundreds of witnesses and covered prominently in Soviet press. Later analyses link the appearance to a Plesetsk-launched Kosmos satellite plume, though the case retained a UFO interpretation in Soviet ufology.
Sources
press: TASS dispatch, 1977-09-23
book: Vallée, Jacques. UFO Chronicles of the Soviet Union (1992)