On what date was the Arecibo message broadcast into space?

The Arecibo message was broadcast into space on 16 November 1974.

The transmission was sent from the Arecibo Observatory in Puerto Rico during a ceremony celebrating improvements to the giant radio telescope. Astronomers aimed it toward Messier 13, a globular cluster in the constellation Hercules roughly 25,000 light-years away.

Frank Drake led the message’s design, with contributions from Carl Sagan and others. Its 1,679 binary digits were chosen because 1,679 is the product of the prime numbers 23 and 73, allowing the data to be arranged as a grid that reveals information about numbers, chemistry, DNA, humans, Earth, and the Solar System.

A common mix-up is treating the message as an ongoing broadcast or a practical conversation attempt. It was transmitted only once and was primarily a demonstration of technological capability. Even a reply from its target would take about 50,000 years for the complete round trip.