The Wow! Signal: 72 Seconds From Somewhere

August 15, 1977. Ohio State's "Big Ear" radio telescope is running an automated SETI sweep when, for 72 seconds, it records a narrowband burst from the direction of Sagittarius — thirty times the background, and sitting almost exactly on 1420 MHz, the hydrogen line: the frequency SETI theorists had long nominated as the natural hailing channel of anyone who knows physics. Days later, astronomer Jerry Ehman reviews the printout, circles the sequence 6EQUJ5, and writes the most famous marginal note in astronomy: "Wow!"

The 72 seconds is itself elegant: exactly the time a fixed point in the sky takes to drift through Big Ear's beam — the signature of a REAL celestial source, not local interference. And then: nothing. The telescope's second beam, minutes behind, heard silence. More than a hundred follow-up searches of those coordinates, some with far bigger dishes, have heard silence since.

The suspect list, fifty years on

Interference reflected off space debris — possible, though the hydrogen band is protected (no legal transmitters). A 2017 comet-hydrogen theory made headlines and was broadly rejected on the physics. Recent archival work suggests candidate stellar mechanisms (a magnetar-like flare stimulating cold hydrogen clouds) — promising, unproven. And the reading Ehman himself grew cautious about but never ruled out: a deliberate transmission, caught once — which is exactly what a rotating or targeted beacon WOULD look like from our side. The signal's tragedy is procedural: one detection is an anecdote, and the universe has declined to repeat itself.

It anchors this archive's sky-file for a reason: it is the cleanest instance of the experience our witnesses describe nightly — something real, recorded, and unrepeatable. The instruments believed. Nobody could do anything further with the belief.