The Wow! Signal
Back in 1977, just a few months before director Steven Spielberg's "Close Encounters of the Third Kind" was released, real-life scientists detected what they at least initially believed was a radio message sent by distant extraterrestrials [source: Kiger].
At Ohio State University's now-defunct Big Ear radio telescope observatory, which at the time was searching for such signals, a volunteer named Jerry Ehman noticed a signal that was extremely powerful -- 30 times louder than the typical ambient noise of deep space -- and extremely close to 1,420 megahertz, the frequency of hydrogen. (This was represented by the "U" in the printout of electromagnetic frequencies from the telescope. Ehman would scan these printouts every day.) But the signal only lasted 72 seconds, and more than 100 subsequent studies of that same region of sky failed to turn up anything unusual. Was the Wow! signal sent by a distant civilization with an extremely powerful transmitter, or just some natural anomaly? Decades later, we still don't know [sources: Wolford, Kiger].