Arecibo message

 Arecibo message

Description

The content of the Arecibo message was designed by Frank Drake, then at Cornell University and creator of the Drake equation, who wrote the message with help from Carl Sagan and others.^[1] The message was meant more as a demonstration of human technological achievement than a serious attempt to enter into a conversation with possible extraterrestrials.^[1] As globular cluster M13, at which the message was aimed, is more than 25,000 light-years from Earth, the message, traveling at the speed of light, will take at least 25,000 years to arrive there. By that time, the core of M13 will no longer be in precisely the same location because of the orbit of the star cluster around the galactic center.^[1] Even so, the proper motion of M13 is small, so the message will still arrive near the center of the cluster.^[5]

The message consists of seven parts that encode the following (from the top down in the image):^[4]

• The numbers one to ten (white)
• The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA) (purple)
• The formulas for the chemical compounds that make up the nucleotides of DNA (green)
• The estimated number of DNA nucleotides in the human genome, and a graphic of the double helix structure of DNA (white and blue, respectively)
• The dimension (physical height) of an average man (blue/white), a graphic figure of a human being (red), and the human population of Earth (white)
• 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, and blue)

The entire 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.^[1][6]

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.^[7] The alternative arrangement, 23 rows by 73 columns, produces an unintelligible set of characters.