On the night of August 15, 1977, just after 11:00 p.m. local time, Ohio State University’s Big Ear radio telescope detected an unusual signal lasting 72 seconds. More than 40 years later, this signal remains unexplained and is still considered the most compelling candidate for evidence of extraterrestrial intelligence. If confirmed, it would represent one of the greatest discoveries in human history—proof that we are not alone.
Interestingly, no human initially observed the signal; instead, it was recorded by an aging mainframe computer at the Big Ear Observatory. The observatory, largely automated, generated printouts of detected signals, which were later reviewed by Dr. Jerry Ehman at his home. A few days after the signal was received, he noticed an extraordinary sequence labeled “6EQUJ5,” the strongest ever detected by the telescope. Stunned by its intensity, he circled it on the printout and wrote a single word beside it: “Wow.”
Upon further analysis, the signal exhibited key characteristics of an artificial extraterrestrial transmission. Its most notable feature was its strength, reflected in the “6EQUJ5” notation, which was not a message but a representation of the signal’s intensity. The system worked by assigning characters based on the strength of incoming radio signals, with numbers ranging from 0 to 9 and letters from A to U representing increasing intensity levels. The WoW! Signal peaked at a level 30 times higher than the background noise.
A natural question arises: Was there any encoded message in the data? The answer appears to be no. The signal was unmodulated, meaning it lacked any recognizable pattern of information, resembling a continuous radio wave rather than a structured transmission. The variation in intensity was attributed to the movement of the radio telescope as the Earth rotated, rather than an intentional modulation from the source. However, it’s worth noting that if the signal contained modulation lasting less than 10 seconds or more than 72 seconds, the telescope would not have been able to detect it.
Crucially, the signal appeared to originate from a fixed point in space. The Big Ear telescope, originally designed for all-sky broadband radio surveys, was later repurposed for SETI (Search for Extraterrestrial Intelligence) to scan for narrowband signals, which are often associated with artificial sources. The WoW! Signal exhibited this narrowband characteristic, making it distinct from typical Earth-based interference.
Another compelling aspect of the WoW! Signal was its frequency. Dr. Ehman determined it to be approximately 1420.4556 MHz—very close to the 1420 MHz frequency of neutral hydrogen, the most abundant element in the universe. SETI researchers have long theorized that any advanced civilization seeking to communicate might use this frequency, as it would be a logical choice known to all radio astronomers. Furthermore, international agreements protect this frequency, meaning no Earth-based transmissions should have been occurring there at the time.
Could the signal have originated from a human-made source? Several possibilities were considered, including spy satellites, but none fit the evidence. The signal matched the Big Ear’s antenna pattern, suggesting it originated from a distant source—at least as far away as the Moon. Low-Earth orbit satellites would have produced a wider pattern. Public satellite records were also checked, and no known satellites were in the signal’s vicinity at the time. A distant satellite beyond the Moon is theoretically possible, but highly unlikely, as broadcasting at a protected frequency would attract unwanted attention from astronomers worldwide.
One curious detail about the signal is its slight shift above 1420 MHz. If this shift was due to a Doppler effect, it would indicate that the source was moving toward Earth at about 10 km/s—a relatively slow speed by cosmic standards. However, some researchers have suggested that the signal was intentionally corrected for Doppler shifts, meaning an advanced civilization may have accounted for the motions of their planet, star system, and the Milky Way to transmit a stable frequency.
Another remarkable feature of the WoW! Signal was its extreme narrowband nature, with a width of approximately 10 kHz—much narrower than typical Earth-based radio or television signals. Natural sources rarely produce such focused signals, except under specific conditions such as natural masers, which do not match the WoW! Signal’s characteristics. Technological transmissions, on the other hand, are typically narrowband to conserve energy and avoid interference.
The exact location of the WoW! Signal remains uncertain. It appeared to originate from one of two possible locations in the constellation Sagittarius. This region of the sky is significant because it includes the plane of our solar system (the ecliptic) and the Milky Way’s central bulge, where billions of stars reside. However, no known star systems in these locations can be definitively linked to the signal. The uncertainty arises because the Big Ear used two feed horns, meaning the signal could have come from either beam. Oddly, only one feed horn detected it, suggesting the signal either turned on or off while being observed—something that remains unexplained.
Despite numerous attempts to detect the signal again, including efforts by the Very Large Array and amateur astronomers like Robert H. Gray, it has never been observed a second time. The inability to confirm the signal is a major problem. In SETI research, a signal must repeat for it to be considered strong evidence of extraterrestrial intelligence. The WoW! Signal, unfortunately, does not meet this criterion. It remains an intriguing anomaly, but without a repeat detection, its origin will remain speculative.
If it were indeed a transmission from an alien civilization, the WoW! Signal would tell us only one thing: an advanced species exists and possesses radio technology. Without modulation or additional context, it would be nothing more than a cosmic “hello,” leaving countless questions unanswered.
Interestingly, the Big Ear telescope detected other unexplained narrowband signals during its operation—over a thousand of them, according to researcher Bob Dixon. However, none were as strong or as striking as the WoW! Signal. Unfortunately, the telescope itself no longer exists, as it was dismantled in the late 1990s and the land was repurposed for a golf course—an ironic end for an instrument that may have once intercepted an extraterrestrial message.
Dr. Jerry Ehman, the astronomer who famously wrote “Wow!” on the printout, remains cautious about interpreting the signal’s origin. Even after more than four decades, it stands as one of the most tantalizing mysteries in the search for extraterrestrial intelligence.
