Word: detectably
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Dates: during 1960-1969
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...unit for measuring relative loudness of sounds, the decibel is approximately the smallest degree of difference that, a human ear can detect between the loudness of two sounds...
...farthest end of the space science spectrum is a project to listen for messages sent by intelligent creatures living on planets revolving around other stars than the sun. This project was made plausible by Harvard's Physics Professor Edward Purcell, who was the first to detect the 21-cm. waves from cold hydrogen throughout space. Purcell explains that if intelligent aliens send messages to the earth, they will use a sort of reversed cipher that is deliberately made easy to translate. Their first problem will be to select the proper radio frequency: there is no use picking one at random...
What message will the aliens send if they want to be understood by earthlings? Purcell suggests that a simple on-off signal will be easiest to detect, and is most likely to be sent. But he speculates that many messages of varying difficulty may be sent simultaneously, which is not hard to do. Aliens on a planet of Epsilon Eridani, a likely star, will not expect to get an answer from the solar system in less than 22 years. But by sending simultaneous messages, they can educate their earthside listeners quickly. Besides simple number series, says Purcell, the messages will...
Discoverer XVIII's primary mission was another step in the perfection of two space-age military reconnaissance techniques: the Samos system for camera detection of such ground-level activity as troop movements, and the Midas early missile-warning system, which is said to detect rocket firings anywhere on earth by means of infra-red sensors...
...regular search of the Caribbean, but would not act to intercept suspicious vessels unless 1) those ships were within the three-mile territorial limits of Nicaragua and Guatemala, and 2) those countries specifically requested the U.S. Navy to intercept. One job of the electronics-crammed destroyers will be to detect small fishing boats or yachts-or possibly foreign submarines-and prevent them from landing shipments of arms at night...