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If an alien civilization tried to reach out to us, how would they do it? Radio waves are the obvious answer; they travel far and only require a small power input. But what type of radio signal would aliens send?
In the early seventies, physicists Phillip Morrison and Giuseppe Cocconi predicted that an alien civilization would transmit a radio signal at 1420 MHz and in a narrow band frequency. Why? An alien signal would have to be something more fundamental and universal than language, something that any intelligent civilization would understand. So why not use a number associated with the most common element in the universe, hydrogen? Hydrogen emits radiation at 1420Mhz. Furthermore, Morrison and Cocconi predicted that an extraterrestrial civilization would send the signal at a narrow band frequency, as narrow band frequency signals require less energy and are created by no natural phenomena.
On August 15, 1977, an exact match for this signal predicted by Morrison and Cocconi arrived on a detector in Delaware, Ohio. Astronomer Jerry Ehman, who first discovered the signal in the data a little while later, christened it the, “Wow!” signal. It has never been explained since.