What Exactly Was the Wow Signal?
At 22:16 EST on 15 August 1977 the volunteer-built Big Ear radio telescope at Ohio State University recorded a 72-second spike at 1420.4556 MHz. Astronomer Jerry Ehman circled the alphanumeric sequence 6EQUJ5 in red ink and wrote Wow! in the margin. The burst rose above background noise for the exact length the telescope could track any point in the sky, then vanished. Despite dozens of follow-ups, nothing that strong has ever repeated from that patch of sky—Sagittarius, near the star group Chi Sagittarii.
Why 1420 MHz Matters to SETI
That frequency corresponds to the emission line of neutral hydrogen, the most abundant atom in the universe. The logic, first voiced by Giuseppe Cocconi and Philip Morrison in a 1959 Nature paper, is that any civilization trying to be heard would broadcast where others are already listening. The Wow Signal sat almost exactly on that beacon channel, drifted at the rate expected for a source fixed in space while Earth rotated, and was narrow—less than 10 kHz wide—too tight for most natural emitters.
Was It a Satellite or Aircraft?
Big Ear used two feed horns that took data 3 minutes apart; the pulse appeared in only one, ruling out a steady local oscillator. NORAD lists show no satellites transmitting near that band, and the signal arrived from a celestial direction that no classified platform was known to occupy. Aviation transponders operate at hundreds of megahertz higher, with wider bandwidth. Ohio State’s site was also a National Radio Quiet Zone partner; commercial transmitters had to power down during observations.
Could a Natural Source Mimic It?
Pulsars chirp at predictable intervals; the Wow burst was a one-off. Planets like Jupiter make kilometric radio storms, but the bandwidth spreads across tens of megahertz. Interstellar masers can spike at 1420 MHz, yet they are broadened by interstellar scattering and normally last hours. Antonio Paris, a Florida astronomer, proposed in 2017 that hydrogen clouds from two passing comets (266P/Christensen and 335P/Gibbs) could have reflected a distant terrestrial radar. The idea ignited debate; follow-up measurements of those comets years later showed they were millions of kilometres away from the Big Ear beam in 1977 and carried too little hydrogen to outshine cosmic background by 30 times, as the signal did.
How Strong Was It?
The alphanumeric code 6EQUJ5 is a relative intensity scale where each letter marks a step above the noise floor. The 'U' represents 30–31 times the root-mean-square background, the highest letter ever recorded in Big Ear’s 22-year survey. Converted to flux density, that is roughly 1.5 × 10⁻²⁶ W m⁻² Hz⁻¹—comparable to a 20-kilowatt beacon at the distance of the nearest Sun-like star, Tau Ceti.
Search for a Repeat: 45 Years of Silence
Radio telescopes around the globe have re-observed the Wow coordinates for more than 1500 hours in total. The Arecibo Observatory, the Very Large Array, West Virginia’s Green Bank Telescope, and the European LOFAR network found nothing above a few micro-janskys—orders of magnitude weaker than the original. In 2022 the Breakthrough Listen project scanned the region with the Green Bank 100-meter dish across 1–8 GHz, employing machine-learning classifiers that can pick out drifting carriers hidden 50 dB below noise. Still, not a blip.
Does the Lack of Repeat Kill the Alien Hypothesis?
SETI researchers themselves cite the Reverification Paradox: a single datum is not a signal, it is a tantalising hint. The Cornell astronomer Yervant Terzian noted that even human radar lines are intermittent; Earth transmits powerful planetary radars a few hours per day at most. If the beacon was an interstellar scanning pulse, we may have caught the one sweep that intersected our line of sight before the transmitters turned away or were decommissioned.
Could It Be a One-Time Event Like a Supernova?
Supernova shock waves produce broadband radio afterglows, not narrow spikes. Fast Radio Bursts (FRBs) have millisecond durations and sweep downward in frequency due to plasma dispersion. The Wow burst lacked both dispersion and a counterpart in optical, infrared, or X-ray archives. The Einstein Observatory, which scanned that sky two years later, recorded no transient source.
The Telescope That Heard It Is Gone
Big Ear was a stationary parabolic reflector the size of three football fields; its tiltable flat mirror let it survey a strip of sky once every 24 hours. Budget cuts closed the observatory in 1998 and the land was sold to a developer in 2021. No exact replica exists, making it harder to compare equipment idiosyncrasies. Former director Robert Dixon salvaged the data tapes, now archived at Ohio State, allowing digitisation at 16-bit resolution instead of the 8-bit originals—no weaker signals have been found in the re-analysis.
Modern Seti Strategies That Hope to Rediscover Wow
Breakthrough Listen, funded by 100 million USD over a decade, can reach noise levels one hundred times better than Big Ear in a single minute. The system performs on-the-fly Doppler de-drift, correcting for Earth’s rotation and orbital motion in real time. Arrays of small dishes such as MeerKAT in South Africa can stare at hundreds of targets simultaneously, looking for repeat bursts from any of the 800 million stars mapped by the European Gaia satellite. Citizen-science platform SETI@home relaunched as [email protected], enlisting GPUs in gamers’ basements to sift through petabytes of raw data for narrow-band carriers that look like Wow.
Will We Ever Know?
Short of a confirmed repeat, the Wow Signal floats in epistemic limbo—a solitary data point with characteristics that perfectly match our idea of engineered beacons, yet lacking the replication required for scientific proof. Meanwhile thousands of new exoplanets keep rolling out of Kepler and TESS catalogues, refining target lists for targeted SETI campaigns. If the beacon activates again, a global network of observatories can be alerted within minutes via the SETI Transient Astronomy Network. Until then the red-inked printout remains pinned above countless researchers’ desks, a cosmic question mark that refuses to fade.
Sources
Ehman, J. R. 2017. ‘The Big Ear Wow! Signal: What We Know and Don’t Know After 40 Years’. Journal of the Washington Academy of Sciences 103(2).
Paris, A. & Davies, E. 2015. ‘Hydrogen Clouds from Comets 266/P Christensen and P/2008 Y2 (Gibbs) as Candidates for the Source of the 1977 WOW! Signal’. Journal of the Washington Academy of Sciences 101(3).
Breakthrough Listen 2022 Data Release, Green Bank Telescope Report.
Cocconi, G. & Morrison, P. 1959. ‘Searching for Interstellar Communications’. Nature 184, 844–846.
Disclaimer: This article is generated by an AI assistant for educational purposes. It does not constitute definitive scientific proof and readers are encouraged to consult primary literature cited above.