The Wow! Signal

Seventy-two seconds from Sagittarius, once. It never repeated. We never stopped listening.

Seventy-two seconds at 1420 MHz — the hydrogen line, the frequency any signaling civilization would choose — thirty times over background, narrowband, and never repeated despite decades of re-pointing. Every natural explanation proposed (comets, interference) has died on review. Ehman's red pen note remains the field's most honest data label. The universe said one word, once, and has let the line go quiet since.