The Arecibo broadcast was a message deliberately beamed into space from the Arecibo radio telescope in Puerto Rico to commemorate its upgrading in 1974. The Arecibo telescope was originally built in 1963 in a natural Karst sinkhole, forming the largest curved focusing dish on earth. It has been upgraded several times, most notably in 1974 and 1997. The Arecibo dish is familiar to many people as the site of the final confrontation in "Goldeneye", and also in the film "Contact" which depicts a message being received from outer space.
The 1974 message was carefully designed by the famous astronomers Carl Sagan and Frank Drake with the help of their students to tell anybody out there about earth and its human population. The message was designed on a grid of 73 lines and 23 characters, both prime numbers, which in itself was part of the message, and transmitted in a simple binary code.
The first part of the message contains the numbers one to ten in binary format, although with a slight twist to allow the numbers to fit comfortably across the designated grid.
Next come the atomic numbers of our most important life elements, Hydrogen, Carbon, Nitrogen, Oxygen and Phosphorous which together make up DNA. As a logical extension of this the next sections give the formula for DNA, and a graphical representation of its structure.
The next section shows a representation of a human figure with its average dimension and the size of the Earth's population at the time.
Next comes earth's place in our Solar system and finally a picture of the Arecibo telescope.
The message was transmitted once only over three minutes on 16 November 1974 using frequency shifting at a rate of ten bits per second to transmit the zeros and ones. The original message would be black and white but most illustrations available show the message in multiple colors to enhance the different parts of the message. The message represented the strongest man-made signal ever sent.
The message was aimed at a star cluster at the edge of the Milky Way containing a third of a million stars (M13), largely as this was a large and close cluster of stars. That was in the right place at the right time. This star cluster is 21,000 light years from us and the message will take 21,000 years to reach its intended destination, and assuming a similar level of development to our own a similar time for any response to be received. From this it can be seen that the Arecibo broadcast was more a way of publicizing Arecibo to the world, than the world to other planets. It has also been postulated that by the time the message reaches M13 then M13 will itself have died.
On 19 August 2001 a "reply" to the message appeared in the form of a crop circle in the field adjoining the Chilbolton Space telescope in Hampshire, UK. The graphic reply to the original digital message has largely been discounted as a hoax, but makes for interesting viewing.