IT was 37 seconds long and came from outer space. On 15 August 1977 it caused astronomer Jerry Ehman, then of Ohio State University in Columbus, to scrawl "Wow!" on the printout from Big Ear, Ohio State's radio telescope in Delaware. And 28 years later no one knows what created the signal. "I am still waiting for a definitive explanation that makes sense," Ehman says.
It came from the direction of Sagittarius; the nearest star in that direction is 220 light years away. If that really is where is came from, it would have had to be a pretty powerful astronomical event - or an advanced alien civilisation using an astonishingly large and powerful transmitter.