AS LONG AS ASTRONOMERS have gazed at the stars and planets, there has been the temptation to see the handiwork of intelligent life when there is no other apparent explanation. Babylonians believed eclipses to be omens sent by gods. Percival Lowell thought he saw canals on Mars. Aware of this history, some astronomers have found humor in it. When pulsars were discovered in the 1960s, says Seth Shostak, the senior astronomer at the SETI Institute in California, "they were first called LGMs, for 'little green men' by the Cambridge astronomers who found them because they didn't know what they were. They were very regular radio sources. Within a year, the theoreticians figured out what they were"- rapidly rotating compact stars emitting radiation like lighthouses. More recently, he notes, a weirdly dimming object called Tabby's Star inspired theories of alien life, before astronomers solved the puzzle.
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