Reverse SETI
Most of SETI is characterized by scanning the stars for messages from other worlds. However, we here on Earth have not been completely silent. Although only a handful of attempts have been made to send messages to other worlds, they show a different side of the curiosity of SETI. We are not only looking, but reaching out as well.
The Arecibo message
One of these attempts was made by the famous Arecibo Observatory. On November 16, 1974, 1,679 bits of information were sent towards the M13 Global Cluster. Travelling at the speed of light, the message should arrive in 25,000 years. The bits of information form a picture, which includes (from the top down) information such as:
- binary representations of the numbers 1- 10
- atomic numbers of the five elements essential to terrestrial life
- the chemical formula of the DNA molecule
- average human height
- world's human population,
- image of a human
- the solar system (with Earth displaced)
- image of the transmitting radio telescope, with its diameter indicated
The Golden Record
Another such attempt to communicate with other worlds were the Voyager space probes. Each vessel carried a disc of information that came to be known as The Golden Record(s).
These records contained much more information then The Arecibo message and the small plates that accompanied Pioneer 10 and Pioneer 11. A committee chaired by SETI fanatic and brilliant astrophysicist Carl Sagan selected the Golden Record contents for NASA. There is an amazing amount of information on the record, which includes:
- 115 images in analog form
- many sounds of nature
- musical selections from different cultures and eras
- spoken greetings from Earth-people in fifty-five languages
Each record is encased in a protective aluminum jacket, together with a cartridge and a needle to play them.
The cover of the record is perhaps the most impressive. It is the key to using and understanding the information. The cover of the Golden Records tells:
- How to play the record
- How to get images from the record
- Where our solar system is, mapped from several known pulsars
- The length of 1 second