Arecibo Message (1974).
documentedresearch_programSETI & Technosignatures
Symbolic 1,679-bit interstellar broadcast aimed at globular cluster M13, designed by Frank Drake, Carl Sagan and colleagues; the canonical active-SETI act.
Transmitted once on 16 Nov 1974 at 2380 MHz to mark the Arecibo telescope upgrade, the message encoded numbers, the elements of DNA, a DNA double helix, a human figure, the Solar System, and the dish itself in a 73×23 bitmap. Aimed at M13 (~25,000 ly), it was symbolic — any reply is tens of thousands of years away. It is the most famous example of METI / active SETI.