On November 16, 1974, a code message was sent from Earth to Messier 13, a globular star cluster located about 25,000 light years from Earth in the constellation Hercules. This was humanity’s first attempt to get in touch with alien life forms.
The message was to demonstrate human technological capabilities, scientific knowledge and information about the position of humanity in the galaxy to possible extraterrestrial intelligence. It was astronomer Frank Drake who composed the message, along with Carl Sagan’s assistance (here you can see Sagan talking about climate change) and other eminent astronomers.
The message consisted of an image of 1679 binary digits (consisting of 210 bytes), rectangularly arranged in 73 lines of 23 characters per line. Binary digits (one and zero) were transmitted by moving the frequency to the 10 bit rate per second. The message was intended to transmit different scientific, geographical, biological and astronomical information.
Today there are many experts who “recommend” to avoid contacting or sending messages to possible alien civilizations. Stephen Hawking himself was a great advocate of the idea of “not disturbing” possible extraterrestrial civilizations; even Michio Kaku, famous astrophysicist and publicizer, recently told the Guardian why we should not contact him.