For years SETI has been looking for messages from outer space, searching the sky for signs that we are not alone in the universe, but while we have been listening rarely have we said anything ourselves. The Arecibo Broadcast is the most powerful of our messages to anyone who might be looking for us.
Sent in 1974 to commemorate the upgrades to the Arechbo Radio Telescope this message consisted of 1679 bits of information arranged into 73 lines with 23 characters per line and was aimed towards the globular star cluster M13, approximately 21,000 light years away. This message was sent for only a few minutes and directional but The emission was equivalent to a 20 trillion watt omnidirectional broadcast, meaning that if a similar message was aimed towards the Arechibo telescope from anywhere in the galaxy it could pick it up.
As a message itself it is unlikely to ever be seen, but it has a second important function. With so little room for information in the message it forced us to think about what message we wanted to send.
The message contains five parts. Each of them designed to help any alien who discovers it understand us better.
The first part of the message are the numbers 1 through 10 designed more to help the aliens who discover it decipher the message than anything else.
Next is a section that explains human DNA, containing the atomic numbers for the elements that make up DNA, the formulas for the sugars and bases in the nucleotides of DNA, the number of nucleotides in our DNA and a graphical representation of the helix structure of DNA.
Next is a stick figure representation of a man.
Forth is a representation of our solar system with Earth marked by being a line above the other planets.
Finally, there is a graphical representation of the Arecibo telescope.
Although this is an extremely simple message it illuminates some of the difficulties that are expected if we are to ever communicate with extra terrestrial beings. From the basic structure of humanity to the use of prime numbers, binary and atomic numbers we have attempted to write in the most basic languages of the universe in the Arecibo broadcast. Yet when this message was given to scientists to decipher on earth it was discovered that no one could decipher the entire thing. Each scientist was instead able to decipher only the part in his field of expertise.
As a introduction to any aliens who might discover the Arecibo broadcast tells them what we are but not who we are. It is unlikely that this message will ever be received it is still out there flying into space as a possible first ambassador to some strange alien race who is asking the same question we are, is there anyone out there.