A warm August night in Ohio. A long, paper printout crawls from a radio telescope’s line printer...digits and letters marking signal strength.
One 72-second burst at 1420 MHz jumps off the page. An astronomer circles it in red ink and writes: “Wow!”
People care because this is one of the cleanest, narrowband radio hits ever logged right on the neutral hydrogen line...astronomy’s favorite “hailing frequency.”
What actually happened
On August 15, 1977, the Big Ear radio telescope, scanning the sky for narrowband beacons, recorded a sharp, non-drifting spike at 1420.4556 MHz (near the 1420.4058 MHz hydrogen line). The detection lasted one full beam transit (~72 seconds), rose and fell as Earth’s rotation would for a fixed sky source, and was narrow enough to look artificial.
Jerry Ehman, a volunteer with the Ohio State SETI project, spotted the outlier days later while reviewing the alphanumeric printouts, circled “6EQUJ5” (a coded intensity sequence), and wrote “Wow!” in the margin.
Follow-up scans of the same sky region—then and in later years—never reproduced the signal. No recording of the actual waveform exists; only the intensity log survives.
Brief timeline after the prose
- Aug 15, 1977: Big Ear logs the 72-second signal near RA 19h22m (epoch 1950), Dec −27°.
- Aug 18–19: Ehman reviews the printout, marks “Wow!”
- Late 1970s–1990s: Multiple re-observations find nothing at the candidate positions.
- 2010s–2020s: Renewed analyses propose origins from deep-space, satellites, comets, or terrestrial RFI; still no consensus.
Key claims and evidence
At issue: Was this a narrowband, sky-fixed emitter (natural or technological), or a one-off artifact from something nearer to home?
- Main claims
- Sky-fixed, narrowband: Signal rose/fell over ~72 s consistent with the telescope’s beam shape and Earth’s rotation.
- On/near the H-line: Frequency choice looks deliberate if technological—minimizes interstellar absorption and is a SETI target.
- No immediate repeat: Extensive revisits failed to find it again.
- Main pieces of evidence
- The “6EQUJ5” intensity sequence on the Big Ear printout (encodes a strong SNR peak).
- Telescope logs showing pointing/beam geometry (two feed horns; two possible declination tracks).
- Archive papers and Ehman’s notes describing equipment state and RFI environment.
- Main contradictions or disputes
- No raw spectrum: Only integrated intensities were saved—no waterfall, no drift rate, no polarization.
- One-off: Lack of replication weakens all astrophysical and ET hypotheses.
- Prosaic contenders: Sidelobe reception of a satellite, military transmission, or (more controversially) a cometary hydrogen-cloud emission near the band.
How people interpret this
- Believer lens (technological signal)
A narrow, non-drifting spike at the H-line that fits a beam transit is exactly what SETI was built to catch. If the transmitter was intermittent or highly directional, missing a repeat is not surprising. - Skeptic lens (prosaic/RFI)
Without a recorded spectrum or second hit, the parsimonious read is radio frequency interference—possibly via sidelobes or transient equipment behavior. The hydrogen-line proximity isn’t exclusive—lots of RF hardware sits near that band. - Middle ground
The data quality is high for intensity vs. time, but incomplete. “Interesting but indeterminate” is the honest box: a genuine sky-fixed source is plausible, yet so is an undetected RFI path. The lack of a repeat is the anchor fact.
“Interesting, if not conclusive.” — the fate of a perfect 72 seconds with imperfect data.
How we’re covering this
We’re treating Wow! as a methods case: what a near-ideal SETI hit looks like—and why logging the spectrum, drift rate, and polarization matters. Our coverage will:
- Separate the beam-transit geometry (hard constraint) from origin stories.
- Lay out replication discipline: same RA/Dec windows, multi-site coordination, spectrum capture, and satellite/airspace deconfliction.
- Host a short toolkit for readers: how to read “6EQUJ5,” what a drift rate means, why hydrogen line matters, and how modern arrays (MeerKAT/ATA) would log a repeat.
Credibility meter (1–5)
- Witnesses: N/A → treated as instrumentation (score = 3 for operator documentation)
Instrument-only event with clear operator notes; no human “eyewitness” claims. - Physical evidence: 2
No stored waveform—only an intensity printout. Strong SNR, but missing spectral metadata. - Documentation: 4
Telescope logs, pointing geometry, operator notes, and decades of follow-up literature. - Expert review: 3
Competing hypotheses remain; no consensus, but sustained technical scrutiny.
Overall: ~3.0 (a textbook SETI-style hit with incomplete data; compelling but unresolved)
Closing
We know Big Ear caught a single, strong, narrowband event at/near the hydrogen line that behaved like a sky-fixed source over a beam transit.
We do not know its drift rate, polarization, exact bandwidth, or repetition...the very clues that would classify it.
If a modern array captures a repeat from the candidate coordinates—with full waterfall and multi-site confirmation—the Wow! Signal would shift from lore to lab. Until then, it’s the most famous 72 seconds in SETI—and a lesson in why saving everything matters.
