The Wow! signal was a transmission detected by the SETI Professor Jerry Ehman in August 1977 while working on a radio telescope in Ohio state. Professor Ehman was so excited, he wrote "wow" in the margins of the print-out on which he detected the transmission.
The signal itself was thirty times stronger than galactic background noise. It was transmitted and received on the twenty-one centimeter frequency, which no satellite transmitters were allowed to use.
The signal was intermittent, like morse code, and seemed to turn itself on while in the radio telescope’s beam. Until 1994, the Wow! signal was considered the best evidence of extraterrestrial intelligence. (TXF: "Little Green Men")