Mysteries of Wow
Stellar Countdown locations. Segment of a skymap detailing Arecibo reobservations.
Click image for larger view.
SETI@home uses the idle time of over four million personal computers to sift through radio data for signals from extraterrestrial civilizations. The three main signal types of interest are:
Gaussians are the power curves produced when the Arecibo beam scans a steady celestial radio source. The signal is weak at first, strong when it is at the center of the beam, and then fades again. This produces a bell shaped power curve known as a gaussian.
Pulses represent any celestial radio signal of a fixed frequency that is distinguishable above the background noise.
Triplets are a sets of 3 equally spaced spikes. Whereas gaussians represent a constant signal from space, triplets may represent a series of pulses transmitted at fixed time intervals. Credit: SETI@home |
Moffett Field - Oct 22, 2003
Of the many "maybe's" that SETI has turned up in its four-decade history, none is better known than the one that was discovered in August, 1977, in Columbus, Ohio. The famous Wow signal was found as part of a long-running sky survey conducted with Ohio State University's "Big Ear" radio telescope.
The Wow signal's unusual nomenclature connotes both the surprise of the discovery and its sox-knocking strength 60 Janskys in a 10 Khz channel, which is more than 50 thousand times more incoming energy than the minimum signal that would register as a hit for today's Project Phoenix.
But is the Wow signal's notoriety merely the triumph of marketing over substance? Could this momentary cosmic burp have really been ET, or was it just random terrestrial interference dressed up with a sexy moniker? For a decade, Robert Gray, a long-time, independent SETI researcher from Chicago, has been trying to find out.
Gray, like many others, was attracted by an intriguing feature of the Wow signal: the manner in which it rose and fell over the course of 72 seconds.
Why is this interesting?
Just this: the Ohio State survey kept the telescope fixed, letting the Earth's daily spin rotate the heavens through its narrow beam. The "beam," of course, was the elongated patch of sky to which the telescope was sensitive - the direction from which it could pick up cosmic signals. The sensitivity was greatest at the center of the beam, falling off to either side.
So as a celestial radio source passed by, it first rose in apparent intensity as Earth's rotation brought it into the beam, reached a peak in the beam center, and then faded away.
Given the size of the Ohio State beam, this rise and fall should take 72 seconds. And for the Wow signal, it did.
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SETI Sets Its Sights On M Dwarfs
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Scientists have been searching actively for signs of intelligent extraterrestrial civilizations for nearly half a century. Their main approach has been to point radio telescopes toward target stars and to "listen" for electronic transmissions from other worlds.
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