320px-Arecibo message.svg

This is the message with color added to highlight its separate parts. The actual binary transmission carried no color information.

1024px-Heart of M13 Hercules Globular Cluster

The heart of Hercules Globular Cluster (Messier 13). The cluster will move through space during the transit time; opinions differ as to whether or not the cluster will be in a position to receive the message by the time it arrives,[1] [2] as it will take nearly 25,000 years for the message to reach its intended destination.[3]

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.[3][4] 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.[5] 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.[3][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. 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.[7]

Frank Drake, then at Cornell University and creator of the Drake equation, wrote the message with help from Carl Sagan, among others.[3] The message consists of seven parts that encode the following (from the top down):[7]

  1. The numbers one (1) to ten (10) (white)
  2. The atomic numbers of the elements hydrogen, carbon, nitrogen, oxygen, and phosphorus, which make up deoxyribonucleic acid (DNA) (purple)
  3. The formulas for the sugars and bases in the nucleotides of DNA (green)
  4. The number of nucleotides in DNA, and a graphic of the double helix structure of DNA (white & blue)
  5. 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)
  6. A graphic of the Solar System indicating which of the planets the message is coming from (yellow)
  7. A graphic of the Arecibo radio telescope and the dimension (the physical diameter) of the transmitting antenna dish (purple, white, & blue)


  1. "It's the 25th anniversary of Earth's first attempt to phone E.T.". 1999-11-12. 
  2. "Science 2.0". In regard to the email from. Retrieved 2015-04-15. 
  3. 3.0 3.1 3.2 3.3 "Cornell News: It's the 25th anniversary of Earth's first (and only) attempt to phone E.T.". Nov 12, 1999. Archived from the original on 2008-08-02. Retrieved 2008-03-29. 
  4. Johnson, Steven (28 June 2017). "Greetings, E.T. (Please Don’t Murder Us.)". The New York Times. Retrieved 28 June 2017. 
  5. Larry Klaes (2005-11-30). "Making Contact". Ithaca Times. Archived from the original on 2009-01-07. Retrieved 2007-07-27. 
  6. Jay M. Pasachoff. "Chapter 20: Life in the Universe". Retrieved 2007-05-05. 
  7. 7.0 7.1 Cassiday, George. "The Arecibo Message". Retrieved 12 Oct 2013.