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270 Would those amateurs be taken seriously by the extraterrestrial equivalent of our scientific community? Or would they be ignored? the cosmos. There is a widespread assumption in the SETI community that more advanced civilizations will detect us, or already have done so, because we have been radiating electromagnetic signals for decades. To this school of thought, there is no point in remaining silent; the extraterrestrials already know that we are here, or detection is inevitable. Sagan and others have claimed that we have revealed ourselves to the Galaxy by mundane military and commercial activities: radio, radar, and television signals expanding outward from Earth at the velocity of light. McDonough, assuming that intelligent aliens would monitor our television broadcasts, thought that we have already given away the deepest secrets of our culture; it is too late to hide our ugly side from the Galaxy.” Despite what science fiction often assumes, our intelligently organized signals such as radio and televison programs are not our most detectable signs. Radar pulses and carrier waves, however mindless they appear, are far more likely to be detected. Woodruff Sullivan and his colleagues, after studying the electromag- netic signature of the Earth, concluded that we would be most detectable by a few powerful military radars and by the video carrier signals of our television broadcasting stations. Alien astronomers using an instrument like the Arecibo radio telescope could detect the Ballistic Missile Early Warning System at about 18 light-years; our UHF television transmitters would be identifiable only 1.8 light-years away—less than half the distance to the nearest star beyond our Sun. Te tian 5 If alien eavesdroppers were equipped with the proposed Cyclops array of radio telescopes (which was never built), they could detect our strongest video carrier signals at about 25 light-years, and our early warning radar signals out to about 250 light-years.*° Though these distances sound impres- sive, they include only a tiny portion of a Galaxy 100,000 light-years across. Currently, our most powerful signals are planetary radar pulses sent from the Arecibo observatory. NASA’s short-lived all-sky survey could have detected transmissions from that instrument’s extraterrestrial analog out to 30 light-years; the targeted search could have seen it at 300 light- years. So far, Arecibo’s pulses have only reached out about 40 light-years. This radar is a very discontinuous source, used for only a few hundred Before Contact They Know We Are Here It is too late to be shy and hesitant. We have announced our presence to Be vane a —Carl Sagan, 1973"