Wow! Signal

Probably one of the most perplexing signals we've ever received, the Wow! Signal continues to elude explanation 40 years after its discovery. There has been no shortage of explanations for what it was, but so far, nothing cuts it.

The signal was detected on 15

August 1977 by an astronomer called Jerry Ehman, using the Big Ear radio telescope in Ohio. The powerful signal was transmitted at a frequency of 1,420 megahertz, the natural emission of hydrogen, and lasted for 72 seconds. It came from the direction of the Sagittarius constellation, and it was so unusual that it led Ehman to circle it with an annotation: “Wow!”

Owing to its frequency, some suggested this may have been an alien transmission, as using the frequency of hydrogen – the most common element in the universe – seems like a smart move. While many favour the alien theory, others have suggested alternatives. For example, it could have simply been a reading from a hydrogen cloud surrounding a comet. Others have suggested Earth-based interference, although this frequency is a protected one that cannot be transmitted on, making that idea unlikely.

Four decades later, we still don't know what caused the Wow! Signal, and the signal has never been observed again. But in 2012, a signal of our own was sent in the direction of the Wow! Signal, so maybe they'll write back.