The Arecibo message was broadcast into space a single time via frequency modulated radio waves at a ceremony to mark the remodeling of the Arecibo radio telescope in Puerto Rico on 16 November 1974.

The message was aimed at the current location of globular star cluster M13 some 25,000 light years away because M13 was a large and close collection of stars that was available in the sky at the time and place of the ceremony.

It consisted of 1,679 binary digits, approximately 210 bytes, transmitted at a frequency of 2,380 MHz and modulated by shifting the frequency by 10 Hz, with a power of 1,000 kW. The "ones" and "zeros" were transmitted by frequency shifting at the rate of 10 bits per second.

The total broadcast was less than three minutes. The cardinality of 1,679 was chosen because it is a semiprime (the product of two prime numbers), to be arranged rectangularly as 73 rows by 23 columns. The alternative arrangement, 23 rows by 73 columns, produces jumbled nonsense.

Dr. Frank Drake, then at Cornell University and creator of the Drake equation, wrote the message with help from Carl Sagan, among others.

Arecibo-Message Description
The Arecibo Message<em>Credit: Arne Nordmann</em>
The Arecibo Message

1. The numbers one (1) to ten (10) (white)

2. The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA) (purple)

3. The formulas for the sugars and bases in the nucleotides of DNA (green)

4. The number of nucleotides in DNA, and a graphic of the double helix structure of DNA (white & blue)

5.  A graphic figure of a human, the dimension (physical height) of an average man, and the human population of Earth (red, blue/white, & white respectively)

6. A graphic of the Solar System indicating which of the planets the message is coming from (yellow)

7. A graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish (purple, white, & blue)

Because it will take 25,000 years for the message to reach its intended destination (and an additional 25,000 years for any reply), the Arecibo message was more a demonstration of human technological achievement than a real attempt to enter into a conversation with extraterrestrials.

In fact, the core of M13, to which the message was aimed, will no longer be in that location when the message arrives. However, as the proper motion of M13 is small, the message will still arrive near the center of the cluster. The real purpose of the message was not to make contact but to demonstrate the capabilities of newly installed equipment.

History of the Future
On the other hand we cannot be sure that "somebody" catches the message on its way to M13. It is like posting an embarassing photo in the former Internet - once you had uploaded it there, you never got it away again - with all consequences. We can only hope that "they" are friendly or too dumb to decypher the position of our home system :-)

This article uses material from these Wikipedia articles which were released under the Creative Commons Attribution-Share-Alike License 3.0: Arecibo_message

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