A Search for Ultra-Narrowband Signals of Extraterrestrial Origin

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Science  25 Aug 1978:
Vol. 201, Issue 4357, pp. 733-735
DOI: 10.1126/science.201.4357.733


Nearly 200 nearby stars similar to the sun were observed at the 21-centimeter neutral hydrogen wavelength (in the heliocentric frame) with a bandwidth of 1 kilohertz and a resolution of 0.015 hertz, using the Arecibo 305-meter antenna. At this resolution the effects of terrestrial interference are so slight that the detection limit of 4 x 10–27 watt per square meter was set by receiver noise alone. No evidence of artificial signals was found.