Arecibo message

The Arecibo message is a radio message that was beamed into space at a ceremony to mark the remodeling of the Arecibo radio telescope in 1974. It was aimed at the globular star cluster M13 some 25,000 light years away and consisted of 1679 binary digits. The number 1679 was chosen because it is the product of two prime numbers and therefore can only be broken down into 23 rows and 73 columns or 73 rows and 23 columns. The information arranged the first way produces jumbled nonsense, but if arranged the second way it forms an image containing information about Earth and the human race. It shows the numbers one through ten, the atomic numbers of hydrogen, carbon, nitrogen, oxygen, and phosphorous, the formulas for the sugars and bases in the nucleotides of DNA, the number of nucleotides in DNA, the double helix structure of DNA, a figure of a human being and its height, the population of Earth, our solar system, and an image of the Arecibo telescope with its diameter.

Because it will take 25,000 years for the message to reach its intended destination of stars (and an additional 25,000 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.

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

Explanation

Numbers

Numbers from 0 to 10 in binary format (the bottom row marks the beginning of each number)

Even knowing binary, the encoding of the numbers may not be immediately obvious due to the way they have been written.
To read the first six digits, ignore the bottom row, and read them as three binary digits from top to bottom.
The readings for 8, 9 and 10 are a little different, as they have been given an additional column to the right of the first, extending the binary to a maximum of 6 digits.
0 0 0 1 1 1 1 00 00 00
0 1 1 0 0 1 1 00 00 10
1 0 1 0 1 0 1 01 11 01
X X X X X X X X X X <-least significant digit marker

DNA elements

The numbers 1, 6, 7, 8 and 15
represent hydrogen (H), carbon (C), nitrogen (N), oxygen (O) and phosphorus (P) respectively.
These are the components of DNA.

Nucleotides

Deoxyribose C₅OH_{7_{, Adenine C_{5_{H₄N₅, Cytosine C₅H₅N₂O₂, Deoxyribose C₅OH₇}}}}

Phosphate PO₄, Phosphate PO₄

Deoxyribose C₅OH_{7_{, Thymine C₅H₅N₃O, Guanine C₅H₄N₅O}}

Phosphate PO₄, Phosphate PO₄

Double helix

DNA double helix (the vertical bar represents the number of nucleotides)

Humanity

The element in the center represents a man. The element on the left indicated the average height of a man: 1764 mm. This corresponds to the horizontally written binary 14 multiplied with the wavelength of the message (126 mm). The element on the right depicts the size of human population encoded with 32 bits: 4'292'591'583

Planets

The solar system: the Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

The Earth is misaligned to show where the message came from.

Telescope

The last part represents the Arecibo radio telescope with its diameter (2430 multiplied with the wavelength gives 306.18 m).

External link

SETI homepage on the message

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