The Arecibo message

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. The message 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. The message forms the image shown on the right, or its inverse, when translated into graphics, characters and spaces.

Dr. Frank Drake, then at Cornell University and creator of the Drake equation, wrote the message with help from Carl Sagan, among others. The message consists of seven parts that encode the following (from the top down):

    1. The numbers one (1) to ten (10)
    2. The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA)
    3. The formulas for the sugars and bases in the nucleotides of DNA
    4. The number of nucleotides in DNA, and a graphic of the double helix structure of DNA
    5. A graphic figure of a human, the dimension (physical height) of an average man, and the human population of Earth
    6. A graphic of the Solar System indicating which of the planets the message is coming from
    7. A graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish

21 years later in 2001, the following "crop circles" appeared in a field near Britain's Chilbolton observatory.

Here's a closer look:

Here it is colorized:

The diagram of the "transmitter" that appears in this message seems similar to the crop circle that appeared in the same field a year earlier in 2000: