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On November 16, 1974, the Arecibo Observatory transmitted at 2380 MHz at an effective bandwidth of 10 Hz a message directed at the globular cluster M13. The message consists of a 1679-bit picture portraying a counting scheme, five biologically significant atoms (H, C, O, N, and P), the genetic structure of the four purines and pyrimidine bases of DNA; a schematic of the DNA double helix with an order-of-magnitude estimate of the number of base pairs; a representation of a human being and his or her dimensions; a depiction of the solar system with an indication that human beings inhabit the third planet and an estimate of the human population of the Earth; and finally, a schematic representation of the Arecibo Observatory and a description of its dimensions. (Source: AreciboObservatory): https://tinyurl.com/y22tmfay
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