The SETI Institute (Search for Extraterrestrial Intelligence) is the organization in charge of searching for possible communications from outer space via radio, optical, or gamma signals by other intelligent life forms.
One way they attempt to pick up signals, is by measuring the frequency of the molecules out in space. For example, hydrogen is the most common element in the universe and resonates at about 1420.40MHz. It is believed that intelligent extraterrestrials would use this frequency to transmit signals as they would know, as we do, that this is the most common element. So researchers focus on the frequency line emitted by hydrogen and have given it a corresponding alphanumeric scale to measure frequency intensity. What? Hard to follow, I know.
Basically the scale picks up space noise. So a 1 on the scale is simply hydrogen and 2 may be the noise emitted by our sun all the way up to 9 after which A-Z are used. The instruments they use. pick up these signals day and night and print them out as they are received, and later reviewed by researchers at the institute. As you can imagine there are a lot of 1’s, 2’s, and 3’s that they see each day. Typical space noise. But at on August 15, 1977, Jerry Ehman was reviewing the printouts when he noticed an unusual spike in the signal. The signal read “6EQUJ5,” which occurred at 10:16pm that night. He took out a red marker and wrote “Wow.”
The technical interpretation of what that number actually means is a bit complicated, but basically this signal was 30 times louder than normal deep space. No signal before or since has ever been recorded.
There is a lot of speculation as to what the signal could have been. Proponents of intelligent extraterrestrial life widely accept this as proof that it exists and that the “Wow signal” was an attempt to make contact. Some may think that this is just a convenient anomaly that’s used to further the research and funding into SETI but the fact is that the “Wow signal” is not so easily dismissed by those who disagree. There are other detailed reasons, not discussed here, that lead many scientists to believe that this may very well be an attempt to make contact. They simply have no explanation as to what else the signal may have been. It doesn’t appear as though the signal could have originated from space from any natural source.