Over a quarter of a century ago on Nov. 16, 1974 we sent the first and only deliberate radio message to extra-terrestrials from the Arecibo radio telescope in Puerto Rico. So far there has been no response, but no problem apparently we weren't expecting one. The message contained some basic information about the human race and included information about the fundamental chemicals of life, DNA, a diagram of 'our' solar system and pictures of human beings.
According to Donald Campbell, a Cornell University professor of astronomy, who was a research associate at the Arecibo Observatory at the time, "It was strictly a symbolic event, to show that we could do it".
Rather than being a serious attempt to communicate with other beings the event was more of a PR stunt designed to show the tremendous power of the newly installed Arecibo's radar transmitter the ability of the telescope's 1,000 foot diameter dish antenna to project a powerful signal into space. But on the day many of those who were present took the event seriously, said Harold Craft, Cornell's vice president for services and facilities, who was then director of observatory. "We translated the radio-frequency message into a warbling audio tone that was broadcast over speakers at the ceremony. When it started, much of the audience spontaneously got up and walked out of the tent and gazed up at the telescope."
As usual in almost any scientific advance there were skeptics who worried that sending the message was dangerous, because it might attract the attention of unfriendly aliens. However this is a very long shot as the chance of the message being detected by some extra-terrestrial's is minute as it was sent only once, over three minutes, on a narrow beam directed toward one group of 300,000 stars called the Great Cluster in Hercules, Messier 13! Being 25,000 light-years away, even with the message moving at the speed of light, it will have only traveled one thousandth of the distance (about 147 trillion miles) by now.
However in a nice twist of fate the cluster which the signal is aimed at won't even exist when the message arrives as normal rotation of the galaxy will have moved it well out of the way by then.
No other formal messages have since been sent, but many radar signals already reach beyond our solar system and hopefully if detected would be seen as being created by intelligent beings (may be we should have sent some Shakespear to really confuse them). Being human we couldn't just rely on an intangible like a radio message so in 1972, a message, engraved on copper plate, accompanied the Pioneer 10 spacecraft. This is estimated to be now about 7 billion miles from Earth.
