Forty-four years ago today, a group of scientists gathered at the Arecibo Observatory amidst the tropical forests of Puerto Rico to humankind’s first attempt at communication with intelligent life beyond our own planet. Their three-minute radio message—a series of exactly 1,679 binary digits (a multiple of two prime numbers) which could be arranged in a grid 73 rows by 23 columns—was aimed at a cluster of stars 25,000 light years away from earth.
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.
This is the message with color added to highlight its separate parts. The actual binary transmission carried no color information.
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 an unintelligible set of characters (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.