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The 1977 Wow! signal lasted 72 seconds, the exact time a telescope could see one spot
Ohio State's Big Ear telescope only observed any given point for 72 seconds as Earth rotated. The signal's full duration at full strength is consistent with a celestial source, not a duration chosen by anything.
On 15 August 1977, Ohio State University's Big Ear radio telescope recorded a narrow-band radio burst so strong and so clean that astronomer Jerry Ehman circled the printout and scrawled "Wow!" beside it. The mark gave the signal its name, but the number that really defines it is 72 — the number of seconds the telescope could listen to any single point in the sky. [1][2]
Big Ear was a transit instrument, not a steerable dish. It simply lay fixed and let Earth's rotation sweep the sky past its beam, like a scanner passing over a page. A source therefore entered the beam, peaked, and left on a fixed schedule set by the telescope's geometry and the planet's spin — and that schedule was 72 seconds at full sensitivity. [1][3]
Why 72 seconds matters
The Wow! signal rose and fell over almost exactly that 72-second window, matching the profile of a small, distant source crossing the beam. That fit is what made it interesting: a terrestrial interference source, an aircraft, or a satellite would generally not mimic the beam's expected shape so neatly. [1][2]
- The signal appeared near the constellation Sagittarius, at a frequency close to the 1420 MHz hydrogen line. [1][2]
- It was detected in only one of Big Ear's two feed horns, not both, which is unusual for a genuine sky source. [1][3]
- Repeated searches of the same region have never detected it again. [2][3]
What the duration does and doesn't prove
The 72-second length is consistent with an extraterrestrial origin, but it is not proof of one. It is equally consistent with any source — natural or artificial — that happened to be in the beam for that period. The mystery is not why the signal lasted 72 seconds; that part is explained by the telescope. The mystery is what was there to be seen. [1][2][3]
- 15 August 1977
Big Ear records the strong narrow-band signal; Jerry Ehman later writes "Wow!" on the printout.
- 1977 onward
Follow-up observations of the Sagittarius region fail to detect the signal again.
- 1990s–present
Big Ear is dismantled; later searches and proposals keep the signal an unexplained case.
Sources
- The 'Wow!' Signal Big Ear Radio Observatory / Ohio State University
- Wow! signal Wikipedia
- Astronomer Jerry Ehman and the Wow! signal Science
