Arecibo message

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The Arecibo message is a 1974 interstellar radio message carrying basic information about humanity and Earth sent to globular star cluster M13 in the hope that extraterrestrial intelligence might receive and decipher it. The 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 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 450 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 number 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 (as do all other X/Y formats). 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):

The numbers one (1) to ten (10) (white)
The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA) (purple)
The formulas for the sugars and bases in the nucleotides of DNA (green)
The number of nucleotides in DNA, and a graphic of the double helix structure of DNA (white & blue)
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)
A graphic of the Solar System indicating which of the planets the message is coming from (yellow)
A graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish (purple, white, & blue)

Since it will take nearly 25,000 years for the message to reach its intended destination (and an additional 25,000 years for any reply), the Arecibo message is viewed as a demonstration of human technological achievement, rather 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. According to the Cornell News press release of November 12, 1999, the real purpose of the message was not to make contact but to demonstrate the capabilities of newly installed equipment.

Video Arecibo message

Explanation

Numbers

  1 2 3 4 5 6 7 8  9  10  ----------------------  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

The numbers from 1 to 10 appear in binary format (the bottom row marks the beginning of each number).

Even assuming that recipients would recognize binary, the encoding of the numbers may not be immediately obvious because of the way they have been written. To read the first seven digits, ignore the bottom row, and read them as three binary digits from top to bottom, with the top digit being the most significant. The readings for 8, 9 and 10 are a little different, as they have been given an additional column next to the first (to the right in the image). This is intended to show that numbers too large to fit in a single column can be written in several contiguous ones, where the additional columns do not have the least-significant-digit marker.

DNA elements

  H C N O P  1 6 7 8 15  ----------  0 0 0 1 1  0 1 1 0 1  0 1 1 0 1  1 0 1 0 1  X X X X X

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

Nucleotides

The nucleotides are described as sequences of the five atoms that appear on the preceding line. Each sequence represents the molecular formula of the nucleotide as incorporated into DNA (as opposed to the free form of the nucleotide).

For example, deoxyribose (C₅H₇O in DNA, C₅H₁₀O₄ when free), the nucleotide in the top left in the image, is read as:

  11000  10000  11010  XXXXX  -----  75010

i.e., 7 atoms of hydrogen, 5 atoms of carbon, 0 atoms of nitrogen, 1 atom of oxygen, and 0 atoms of phosphorus.

Double helix

  11  11  11  11  11  01  11  11  01  11  01  11  10  11  11  01  X

  1111111111110111 1111101101011110 (binary)  = 4,294,441,822 (decimal)

DNA double helix; the vertical bar represents the number of nucleotides. The value depicted is around 4.3 billion, which was believed to be the case in 1974 when the message was transmitted. It is currently thought that there are about 3.2 billion base pairs in the human genome.

Humanity

    ?             X011011    |              111111    |              110111  X0111            111011    |              111111    v              110000

  1110 (binary) = 14 (decimal)

  000011 111111 110111 111011 111111 110110 (binary)  = 4,292,853,750 (decimal)

The element in the center represents a human. The element on the left (in the image) indicates the average height of an adult male: 1.764 m (5 ft 9.4 in). This corresponds to the horizontally written binary 14 multiplied by the wavelength of the message (126 mm). The element on the right depicts the size of human population in 1974, around 4.3 billion. In this case, the number is oriented in the data horizontally rather than vertically. The least-significant-digit marker is in the upper left in the image, with bits going to the right and more significant digits below.

Planets

                    Earth  Sun Mercury Venus       Mars Jupiter Saturn Uranus Neptune Pluto

The solar system, showing the Sun and the planets in the order of their position from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. (Pluto has since been reclassified as a dwarf planet by the International Astronomical Union, but it was still considered a planet at the time the message was transmitted.)

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. Additionally, the human figure is shown just above the Earth graphic.

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

Telescope

  bottom two rows:       100101  <--- 111110X --->

  100101 111110 (binary) = 2,430 (decimal)

The last part represents the Arecibo radio telescope with its diameter: 2,430 multiplied by the wavelength gives 306.18 m (1,004 ft 6 in). In this case, the number is oriented horizontally, with the least-significant-digit marker to the lower right in the image. The part of the image that looks like a letter "M" is there to demonstrate to the reader of the message that the curved line is a paraboloid mirror.

Maps Arecibo message

Message as binary string

  00000010101010000000000  00101000001010000000100  10001000100010010110010  10101010101010100100100  00000000000000000000000  00000000000011000000000  00000000001101000000000  00000000001101000000000  00000000010101000000000  00000000011111000000000  00000000000000000000000  11000011100011000011000  10000000000000110010000  11010001100011000011010  11111011111011111011111  00000000000000000000000  00010000000000000000010  00000000000000000000000  00001000000000000000001  11111000000000000011111  00000000000000000000000  11000011000011100011000  10000000100000000010000  11010000110001110011010  11111011111011111011111  00000000000000000000000  00010000001100000000010  00000000001100000000000  00001000001100000000001  11111000001100000011111  00000000001100000000000  00100000000100000000100  00010000001100000001000  00001100001100000010000  00000011000100001100000  00000000001100110000000  00000011000100001100000  00001100001100000010000  00010000001000000001000  00100000001100000000100  01000000001100000000100  01000000000100000001000  00100000001000000010000  00010000000000001100000  00001100000000110000000  00100011101011000000000  00100000001000000000000  00100000111110000000000  00100001011101001011011  00000010011100100111111  10111000011100000110111  00000000010100000111011  00100000010100000111111  00100000010100000110000  00100000110110000000000  00000000000000000000000  00111000001000000000000  00111010100010101010101  00111000000000101010100  00000000000000101000000  00000000111110000000000  00000011111111100000000  00001110000000111000000  00011000000000001100000  00110100000000010110000  01100110000000110011000  01000101000001010001000  01000100100010010001000  00000100010100010000000  00000100001000010000000  00000100000000010000000  00000001001010000000000  01111001111101001111000