One summer night in 1977, Jerry Ehman, a volunteer for SETI, or the Search for Extraterrestrial Intelligence, may have become the first man ever to receive an intentional message from an alien world. Ehman was scanning radio waves from deep space, hoping to randomly come across a signal that bore the hallmarks of one that might be sent by intelligent aliens, when he saw his measurements spike. The signal lasted for 72 seconds, the longest period of time it could possibly be measured by the array that Ehman was using. It was loud and appeared to have been transmitted from a place no human has gone before: in the constellation Sagittarius near a star called Tau Sagittarii, 120 light-years away.
The signal was, in fact, so remarkable that Ehman circled it on the computer printout, writing “Wow!” in the margin — and unintentionally giving the received radio signal the name under which it would become famous.Despite a lot of effort, no identification has been found for the signal’s source, and no repeat signal has ever been found. It’s a complete mystery. The only conclusion that can be drawn is if the signal truly did originate in deep space, then it was either an astrophysical phenomenon of which we’ve never seen before, or it truly was an intercepted alien signal.