Designed by astrophysicist Frank Drake (see previously) with input from Carl Sagan and others as a proof-of-concept demonstration rather than an attempt to enter into to dialogue with extra-terrestrials and criticised as being too low-resolution to be recognisable to future recipients, the Arecibo Message (see 
also here and here) was beamed from the radio observatory in Puerto Rico on this date in 1974, aimed in the direction of the globular star cluster M13, some twenty-five thousand light-years from Earth. When encoded graphically, the some sixteen hundred bits of data produce the pictured image with seven elements, from top to bottom: the decimal system, the valance of the elements that make up DNA, the chemical formula for the constituent nucleotides, the approximate number of said organic molecules in the human genome with representation of the double-helix structure, the average dimensions of a human male plus the Earth’s population (four billion, compared to eight billion presently), a representation of the Solar System and finally in purple, the Arecibo telescope. The precise number of bits, 1 679, is a semiprime—that is, the product of two prime numbers, seventy-three and twenty-three, to prompt one toward the right orientation, the alternate arrangement producing static. An answer came in 2001 in the form of a crop circle near the Chilbolton radio telescope in Hampshire—rather intricately replacing the carbon-based DNA with silicon and the pictogram of the human figure looks alien—though this reply was unfortunately an elaborate hoax.
