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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Wow! signal | 2/3 | https://en.wikipedia.org/wiki/Wow!_signal | reference | science, encyclopedia | 2026-05-05T13:18:23.464156+00:00 | kb-cron |
=== Time variation === At the time of the observation, the Big Ear radio telescope was only adjustable for altitude (or height above the horizon), and relied on the rotation of the Earth to scan across the sky. Given the speed of Earth's rotation and the spatial width of the telescope's observation window, the Big Ear could observe any given point for just 72 seconds. A continuous extraterrestrial signal, therefore, would be expected to register for exactly 72 seconds, and the recorded intensity of such a signal would display a gradual increase for the first 36 seconds—peaking at the center of the observation window—and then a gradual decrease as the telescope moved away from it. All these characteristics are present in the Wow! signal.
== Celestial location ==
The precise location in the sky where the signal apparently originated is uncertain due to the design of the Big Ear telescope, which featured two feed horns, each receiving a beam from slightly different directions, while following Earth's rotation. The Wow! signal was detected in one beam but not in the other, and the data was processed in such a way that it is impossible to determine which of the two horns received the signal. There are, therefore, two possible right ascension (RA) values for the location of the signal (expressed below in terms of the two main reference systems):
In contrast, the declination was unambiguously determined to be as follows:
The galactic coordinates for the positive horn are l=11.7°, b=−18.9°, and for the negative horn l=11.9°, b=−19.5°, both being therefore about 19° toward the southeast of the galactic plane, and about 24° or 25° east of the Galactic Center. The region of the sky in question lies northwest of the globular cluster M55, in the constellation Sagittarius, roughly 2.5 degrees south of the fifth-magnitude star group Chi Sagittarii, and about 3.5 degrees south of the plane of the ecliptic. The closest easily visible star is Tau Sagittarii. Initially, no nearby Sun-like stars were known to lie within the antenna coordinates, although in any direction, the antenna pattern would encompass about six distant Sun-like stars as estimated in 2016. In 2022, a paper published in the International Journal of Astrobiology identified three likely Sun-like stars within the antenna-pointed coordinates. The better characterized star, 2MASS 19281982-2640123, is located 1,800 light-years away, only 132 light-years away from Maccone's estimation, where an intelligent civilization is more likely to exist. The other two candidates, 2MASS 19252173-2713537 and 2MASS 19282229-2702492, were insufficiently characterized but still likely to be Sun-like stars. Also, 14 other catalogued stars at the antenna coordinates may still turn out to be similar to the Sun after more data becomes available. As a response to the discovery, Breakthrough Listen conducted the first targeted search for the Wow! Signal in its first collaboration between the Green Bank Telescope and the Allen Telescope Array of the SETI Institute. The observations were performed on May 21, 2022, lasting 1 hour from Greenbank, 35 minutes from ATA, and 9 minutes and 40 seconds simultaneously. No technosignature candidates were found.
== Hypotheses on the signal's origin == Interstellar scintillation of a weaker continuous signal—similar in effect to atmospheric twinkling—could be an explanation, but that would not exclude the possibility of the signal being artificial in origin. The significantly more sensitive Very Large Array did not detect the signal, and the probability that a signal below the detection threshold of the Very Large Array could be detected by the Big Ear due to interstellar scintillation is low. Other hypotheses include a rotating lighthouse-like source, a signal sweeping in frequency, or a one-time burst. Ehman said in 1994: "We should have seen it again when we looked for it 50 times. Something suggests it was an Earth-sourced signal that simply got reflected off a piece of space debris." He later somewhat recanted his skepticism, after further research showed the unrealistic requirements that a space-borne reflector would need to have to produce the observed signal. The signal's frequency of 1420 MHz is also part of a protected spectrum: a frequency range reserved for astronomical research in which terrestrial transmissions are forbidden, although a 2010 study documented several instances of terrestrial sources either interfering from adjacent frequency bands or illegally transmitting within the spectrum. In a 1997 paper, Ehman resists "drawing vast conclusions from half-vast data"—acknowledging the possibility that the source may have been military or otherwise a product of Earth-bound sources. In a 2019 interview with John Michael Godier, Ehman stated: "I'm convinced that the Wow! signal certainly has the potential of being the first signal from extraterrestrial intelligence." METI president Douglas Vakoch told Die Welt that any putative SETI signal detections must be replicated for confirmation, and the lack of such replication for the Wow! signal means it has little credibility. In August 2024, the Planetary Habitability Laboratory published a preprint reporting observations made in 2020 at the Arecibo Observatory in Puerto Rico, where they conclude that the Wow! signal was likely caused by a rare astrophysical event, in which stellar emissions energizing a cold hydrogen cloud caused it to suddenly surge in brightness.
=== Discredited hypotheses === In 2017, Antonio Paris, Assistant Professor of Astronomy and Astrophysics at St. Petersburg College, Florida, proposed that the hydrogen cloud surrounding two comets, 266P/Christensen and 335P/Gibbs, now known to have been in the same region of the sky, could have been the source of the Wow! signal. This hypothesis was dismissed by astronomers, including members of the original Big Ear research team, as the cited comets were not in the beam at the correct time. Furthermore, comets do not emit strongly at the frequencies involved, and there is no explanation for why a comet would be observed in one beam but not in the other.