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. This assumes that those who read it will choose to arrange it as a quadrilateral. The information arranged the first way (23 rows, 73 columns) produces jumbled nonsense, but if arranged the second way (73 rows, 23 columns) it forms the image shown on the right, which is assumed to be recognizable as data.

Reading from right to left and from top to bottom, it states (or shows) the following:

the numbers one (1) through ten (10);
the atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus;
the formulas for the sugars and bases in the nucleotides of Deoxyribonucleic acid (DNA);
the number of nucleotides in DNA;
a graphic of the double helix structure of DNA;
a graphic figure of a man and the dimension (physical height) of an average man;
the human population of Earth;
a graphic of the solar system, i.e. Earth's solar system; and
a graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish.

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. Whether this message will have any effects is debatable.

Explanation

Numbers

Read from right to left, the numbers from 1 to 10 appear 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 seven digits, ignore the bottom row, and read them as three binary digits from bottom to top. The readings for 8, 9 and 10 are a little different, as they have been given an additional column to the left of the first. This is probably intended to show that numbers too large to fit in a column can be written in several contiguous ones, where the contiguous columns don't have the base marker.

00 00 00 1 1 1 1 0 0 0 01 00 00 1 1 0 0 1 1 0 10 11 10 1 0 1 0 1 0 1 X X X X X X X X X X <-least significant digit marker

DNA elements

Reading from right to left, the numbers 1, 6, 7, 8 and 15 appear, which are the atomic numbers of hydrogen (H), carbon (C), nitrogen (N), oxygen (O) and phosphorus (P). These are the components of DNA.

The numbers 8 and 15 are written in a logical extension of binary encoding, rather than with the contiguous columns method shown in the message's top number figures:

15 8 7 6 1

-- 1 1 0 0 0 1 0 1 1 0 1 0 1 1 0 1 0 1 0 1 X X X X X

Nucleotides

The nucleotides are described as a sequence of the 5 atoms that appear on the preceding line. They are read from right to left.

For example, the first nucleotide, deoxyribose (C₅OH₇) is read as:

00011 00001 01011 XXXXX

which is, 7 (=111 in binary) atoms of hydrogen, 5 (=101 in binary) atoms of carbon, 0 atoms of nitrogen, 1 atom of oxygen and 0 atoms of phosphorus.

The readings (right to left) are:

Deoxyribose (C₅OH₇), Adenine (C₅H₄N₅), Thymine (C₅H₅N₂O₂), Deoxyribose (C₅OH₇).

Phosphate (PO₄), Phosphate (PO₄).

Deoxyribose (C₅OH_{7_{), Cytosine (C₄H₄N₃O),
Guanine (C₅H₄N₅O), Deoxyribose (C₅OH₇).}}

Phosphate (PO₄), Phosphate (PO₄).

Double helix

DNA double helix (the vertical bar represents the number of nucleotides, but the value depicted is 4.2 billion when in fact there are about 3.2 billion base pairs in the human genome).

Humanity

The element in the center represents a man. The element on the right 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 left depicts the size of human population in 1974 encoded with 32 bits: 4'292'853'750 (in hex: 0xffdfbff6). Note that the "least significant digit marker" is to the upper right.

Planets

The solar system from right to left, showing the Sun and the nine planets in the order of their position (i.e. first planet, second planet, etc.) from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

The Earth is the third planet from the Sun - its graphic is shifted up to identify it as the planet from which the signal was sent.

In addition to showing position, the graphic provides a general, not-to-scale size reference of each planet and the Sun.

Telescope

The last part represents the Arecibo radio telescope with its diameter (2430 (0x97e) multiplied with the wavelength gives 306.18 m). In this case the "least significant digit marker" is lower left pixel of the central group.

Crop circle

A crop circle containing a modified form of the Arecibo message was found near Chilbolton's Observatory, depicting a grey in place of the human figure. It is generally believed to be a hoax. (The Chilbolton 'Arecibo message' Formation)

External links

SETI

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