In 1974 this was the first message ever deliberately beamed into space. It was made from Puerto Rico as part of the ceremonies held to mark a major upgrade to the Arecibo Radio Telescope and was aimed at the star cluster M13, roughly 21,000 light-years away.
This type of message was first conceived of by Frank Drake and the idea was explored by The Order of the Dolphin as a good method of encoding and conveying information into space with Radio Telescopes.
The message was supposed to convey several pieces of information including:
the Arecibo telescope
a man
a double helix meant to represent DNA
the solar system
The transmission was made for only three minutes and was largely a symbolic effort. It is unlikely it will ever be received by another intelligent life form. However, mankind has been unintentionally transmitting signals for decades - mainly in the form of high-frequency television, radio, and radar signals that bleed off into space. The oldest of our TV signals have already reached several thousand other star systems. So who knows - while we are actively listening for signs of ET, we may be communicating our own existence by accident!
