1977年8月15日22时16分（美国东部标准时间），位于美国俄亥俄州的俄亥俄州立大学Big Ear射电望远镜捕捉到一个强烈的窄带无线电信号[1]。该信号来自人马座方向，频率为1420.4556±0.005 MHz（距离氢线频率50±5 kHz），信号强度为背景噪声上方30至31个标准差，带宽小于10 kHz，观测窗口为72秒[1]。天文学家杰瑞·埃曼在审查记录数据时发现了这一异常现象，在计算机打印输出上标记了信号强度代码"6EQUJ5"，并在旁边写下"Wow!"的注释[1]。
这个信号因其特征而引发了关于外星起源的推测。尽管进行了多次后续搜索和假设分析，该信号从未再次出现，其真实起源至今未被确认解释[1]。2019年，埃曼在接受采访时表示："我确信Wow!信号确实有可能成为来自外星智慧生命的第一个信号"[1]。2022年5月21日，突破聆听项目进行了首次针对Wow!信号的目标搜索，但未发现技术信号候选[1]。2024年8月，波多黎各阿雷西博天文台发布预印本报告，认为Wow!信号可能是由罕见的天体物理事件引起的[1]。
On August 15, 1977, at 22:16 Eastern Standard Time, the Big Ear radio telescope at Ohio State University detected a powerful narrowband radio signal originating from the constellation Sagittarius [1]. Astronomer Jerry Ehman discovered the anomaly while reviewing recorded data and marked the signal strength as "6EQUJ5" on the computer printout, annotating it with the now-famous exclamation "Wow!" [1].
The signal exhibited several characteristics that captured scientific attention [1]. It operated at a frequency of 1420.4556 ± 0.005 MHz, approximately 50 ± 5 kilohertz away from the hydrogen line frequency, with a bandwidth smaller than 10 kilohertz and a maximum intensity 30–31 standard deviations above background noise [1]. The observation window lasted 72 seconds, and the signal's position was pinpointed to coordinates in Sagittarius at RA 19h25m ± 5s and Dec −27°03' ± 20', or alternatively RA 19h28m ± 5s and Dec −27°03' ± 20' [1]. Despite numerous subsequent searches and theoretical analyses, the signal never reappeared, leaving its origin unconfirmed to this day [1].
In a 2019 interview, Ehman expressed his conviction that the Wow signal "could indeed potentially be the first signal from extraterrestrial intelligent life" [1]. However, alternative explanations have emerged over the decades. In August 2024, researchers at the Arecibo Observatory in Puerto Rico released a preprint report proposing that the Wow signal may have resulted from a rare astrophysical event [1]. In May 2022, Breakthrough Listen conducted the first targeted search specifically for Wow signal-like transmissions but identified no candidate technological signals [1].