Observed facts
- The signal was recorded on August 15, 1977, and lasted 72 seconds—the length of time a fixed source would take to drift through the telescope beam.
- It was close to the neutral-hydrogen frequency used by many searches for narrowband astronomical signals.
- Repeated searches have not recovered the same signal from the same direction.
Leading scientific explanations
- A rare natural radio transient or hydrogen-cloud interaction could imitate a narrowband source.
- Terrestrial interference, a reflection, or an instrument artefact remains possible.
- An artificial origin is a hypothesis, not an observation or a conclusion.
What remains uncertain
Because the event was never repeated and the original observing record was limited, its source cannot be identified with confidence.