November 16, 1974. This is the anniversary of the most powerful broadcast ever deliberately beamed into space with the intention of contacting alien life. The broadcast formed part of the ceremonies held to mark a major upgrade to the Arecibo Radio Telescope in Puerto Rico.
The broadcast consisted of a pattern of binary numbers. This message contained information about the basic chemicals of life, the structure of DNA, Earth’s place in our solar system and even a stick figure of a human. Click here for an explanation of each part of the message.
It took three minutes to send 1,679 bits of information – a snail’s pace compared to modern computer modems. According to the SETI Institute:
The broadcast was particularly powerful because it used Arecibo’s megawatt transmitter attached to its 305 meter antenna. The latter concentrates the transmitter energy by beaming it into a very small patch of sky. The emission was equivalent to a 20 trillion watt omnidirectional broadcast, and would be detectable by a SETI experiment just about anywhere in the galaxy, assuming a receiving antenna similar in size to Arecibo’s.
At the time, some people expressed concern. They felt we shouldn’t be attempting to reveal Earth’s location in space to unknown alien civilizations. The 1974 signal went out in the direction of M13, a globular star cluster orbiting the center of our Milky Way galaxy. It was chosen mainly because it’s a large collection of stars, that was available in the sky at the time and place of the ceremony
Global star clusters are very far away. M13 is about 23,000 light-years from Earth.
The 1974 signal is 39 light-years from us today.
Bottom line: The first radio signal intentionally sent to space with the idea of contacting alien life was beamed outward from the Arecibo radio telescope in Puerto Rico on November 16, 1974.