![]() As a result some astronomers mayīring a certain expectation to a radio signal, an expectation that it's going So in the early decades of SETI, that's the frequency that most people chose to listen at.Īstronomers generally look at things like stars, things that aren't quiteĮternal, but that last for a really long time. ![]() There weren't a lot of frequencies that had that natural characteristic. It's the wave you can use to map the gas in galaxies, so it's a natural "channel" for astronomers to look at. If you imagine that there are all of these radio astronomers around the universe looking at the stars with big antennas, which is what you need to pick up a signal from that far, chances are that they too would be listening at the frequency of hydrogen, because there is so much of it around. At the time, it was one of the few interstellar emission lines that was known, and a lot of radio observatories had a receiver that could pick it up so it was especially convenient to look for broadcasts there. In the early sixties when people started thinking about the possibility of detecting extraterrestrial broadcasts with radio telescopes, one of the first frequencies suggested was the frequency that interstellar hydrogen glows at. Gray: Well there's a little history there. Seeing the consecutive letters, the mark of something strange or even alien, Ehman circled them in red ink and wrote "Wow!" thus christening the most famous and tantalizing signal of SETI's short history: The "Wow!" signal. As the telescope swept across the sky, it momentarily landed on something quite extraordinary, causing the signal to surge and the computer to shift from numbers to letters and then keep climbing all the way up to "U," which represented a signal thirty times higher than the background noise level. The low numbers represent background noise, the low hum of an ordinary signal. He was flipping through the computer printouts generated by the telescope when he noticed a string of letters within a long sequence of low numbers-ones, twos, threes and fours. Despite its potential import, several days went by before Jerry Ehman, a project scientist for SETI, noticed the data. The telescope was searching the sky on behalf of SETI, the Search for Extraterrestrial Intelligence, and the signal, though it lasted only seventy-two seconds, fit the profile of a message beamed from another world. Late one night in the summer of 1977, a large radio telescope outside Delaware, Ohio intercepted a radio signal that seemed for a brief time like it might change the course of human history.
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