Arecibo Message was written by Dr. Frank Drake and Carl Sagan which was blasted towards the
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Arecibo Message
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M13 star cluster in 1974. It's composed of semi prime no. of binary digits conveying some info about us and it should reach the center of M13 cluster in about 25,000 years at which point something intelligent lives there and detects it. They can respond and there response will return to us in another 25,000 years later.
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M 13
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But Earth has also been broadcasting it's radio and Television signals into space. Currently it is about 200 light years in diameter, compared to the Milky Way it's about that big Aliens within that bubble could tune in and listen to programs we sent out through our aerowaves but these signals thin out the bubble expands across very large distance they may be essentially impossible to tune into. May be a physical Time Capsule would be more permanent but it can't be buried on earth, if earth is about to ravage, a Time Capsule in orbit might be smart like LAGEOS I,
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LAGEOS I
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a satellite put into orbit in 1976, that allows for very precise laser measurement of positions on earth but also contains a Plaque, designed by Carl Sagan upon which is written from number 1 to 10 in binary and the arrangement of the earth's continent 250 million years ago.
