Wow!: The Signal from Sagittarius

To understand why the signal Eamon found that morning was so extraordinary, you have to understand what he and his colleagues had been listening for.

In 1959, in the journal Nature, two physicists at Cornell University named Giuseppe Cocconi and Philip Morrison had published a short paper.

The paper was titled Searching for Interstellar Communications.

Its premise was simple and, at the time, radical.

If intelligent civilization existed elsewhere in the galaxy, Cocconi and Morrison argued, and if they were wanting to signal their existence to other civilizations, they would have to choose some frequency on which to send their signal.

Any frequency chosen would be essentially arbitrary.

The physical universe does not care whether intelligent species chooses to broadcast at 100 megahertz or 1000 megahertz.

But these aliens would face a puzzle.

How could they possibly know which frequency the recipients of their message would be listening on? Cocconi and Morrison proposed a solution.

Any intelligent civilization, they argued, must know about hydrogen.

Hydrogen is the most abundant element in the universe.

It emits naturally at a specific radio frequency of 1420 MHz.

Any species doing radio astronomy at all would inevitably discover this frequency, because they would encounter it in their observations of interstellar hydrogen clouds.

Therefore, if you were an alien civilization trying to signal to whoever was out there, the 1420 MHz frequency would be the obvious choice.

Everyone would be listening there.

Everyone would know why.

The 1420 MHz frequency became known in the years that followed as the hydrogen line.

It sits in the electromagnetic spectrum in a narrow band that Coney, Morrison and subsequent astronomers called the waterhole.

band was quiet it was largely free of natural galactic noise and later when the search for extraterrestrial intelligence became a formal scientific enterprise international agreements protected the 1420 megahertz band from most terrestrial and space-based rodeo broadcasts it was essentially an interstellar radio frequency reserved for possible cosmic communication The first serious attempt to actually listen to signals at the hydrogen line was made by an astronomer named Frank Drake in 1960.

He called it Project OSMA.

He listened for two months at two specific nearby stars, but heard nothing.

Over the following decade, other radio astronomers took up the same idea.

Slowly, tentatively, the field that would come to be called SETI, the search for extraterrestrial intelligence, took shape.

and in 1973 an existing radio observatory in Delaware, Ohio was formally assigned to the SETI program.

The Ohio State University Radio Observatory, or OSURO, was not a beautiful telescope.