Wow! Signal (1977).
allegedscientific_anomalySETI & Technosignatures
Strong (~30σ) narrowband 1420 MHz burst recorded by Ohio State's Big Ear; Jerry Ehman wrote 'Wow!' Never recurred; no confirmed explanation.
On 15 Aug 1977 the Big Ear telescope recorded a 72-second narrowband (<10 kHz) signal near the hydrogen line from the direction of Sagittarius. The intensity code '6EQUJ5' (rising-then-falling intensity, not a message) matched a transiting celestial source. Despite many follow-up searches (Gray, Harp et al. 2020, Perez et al. 2022) it never recurred. The signal itself is documented; its origin is unconfirmed. A 2024–25 Arecibo-archive study proposes a transient neutral-hydrogen cloud brightening rather than ETI.