Alien cultures more advanced than our own have spotted us by now, say astronomers. Within 15 years, our own next-generation telescopes will be searching the skies for the tell-tale rainbows from inhabited planets.

?Our own Earth has been putting out a signal for a billion years,? says astronomer Roger Angel of the University of Arizona in Tucson. ?Any civilization slightly more advanced than our own would know there was life on this planet.?
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