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B Arecibo message

  1. Feb 18, 2017 #1
    I read quite often on this forum and elsewhere that radio signals emitted into space fade enough after a few hundred light years that they are no longer discernible. How do we expect the Arecibo message to be received some 25,000 years from now?
  2. jcsd
  3. Feb 18, 2017 #2
    There is some wishful thinking in this idea.
    It is possible though that another civilization could have found better ways to detect a signal out of noise.
  4. Feb 18, 2017 #3


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    It depends on the power of the initial transmission, which I don't know. Since Arecibo observatory consists of a large spherical reflector, the gain compared to an isotropic antenna is quite large, so I assume anyone within 25,000 light years that is in the the general direction of the broadcast could pick it up with similar technology given the right initial transmit power.

    Most radio signals broadcasted from Earth are made by isotropic antennas, probably with far less power, so that by the inverse square law after a few hundred light years they're no longer discernible above the background noise.
  5. Feb 18, 2017 #4
    Here's what the Site has to say.
    "In 1974, the most powerful broadcast ever deliberately beamed into space was made from Puerto Rico.
    The broadcast was particularly powerful because it used Arecibo's megawatt transmitter attached to its 305 meter antenna. The latter concentrates the transmitter energy by beaming it into a very small patch of sky. The emission was equivalent to a 20 trillion watt omnidirectional broadcast, and would be detectable by a SETI experiment just about anywhere in the galaxy, assuming a receiving antenna similar in size to Arecibo's."
  6. Feb 19, 2017 #5
    Maybe we should also be directing these powerful signals toward closer stars like Centauri and Sirius. It would be a shame if there was intelligent life there and we haven't detected them yet because we hadn't tried contacting them yet.
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