So here's how one learns new / old information in the age of the Internet. Inspired by this beautiful Sagan / Hawking mashup, Trev and I re-watched our 25th Anniversary Cosmos DVDs. When we got to the segment on the search for extraterrestrial intelligence, Trev moseyed over to the SETI site and found this tidbit about a thing called the Wow Signal. Turns out that in 1977 a researcher at Ohio State detected, via OSU's radio telescope Big Ear, a strong signal that bore several key indications of extraterrestrial and artificial origin. He was so impressed he wrote "Wow!" next to the code on the printout. Many attempts, over many years, to detect this signal again have failed. So it could well be some kind of anomolous, natural energy burst. Besides, if aliens were trying to contact us, why wouldn't they repeat the signal?
Well, in 1974, the Arecibo Observatory zapped a message out toward M13 (which will take 25,000 years to get there). And they only did it once.
Note: the Wow Signal is also the name of a band.