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The Arecibo message is a 1,679-bit interstellar radio transmission sent from the Arecibo Observatory in Puerto Rico on November 16, 1974, at 1700 GMT.1 It was directed at the globular cluster Messier 13 in the constellation Hercules, approximately 25,000 light-years from Earth.1 The transmission was a demonstration of the observatory's newly upgraded radio transmitter, not a serious attempt at interstellar communication.1
The message was transmitted during a ceremony marking the completion of a major renovation of the Arecibo telescope.3 The upgrades included a new aluminum surface for the 1,000-foot-wide (305 m) reflector dish and a high-power radio transmitter.3 Frank Drake, then director of the National Astronomy and Ionosphere Center, organized the ceremony and invited over 200 guests.3 U.S. Representative John Davis of Georgia gave the go-ahead for the transmission by paraphrasing a Daniel Webster quote that hangs in the House of Representatives.3
M13 was chosen as the target because it happened to be overhead at the time of the ceremony.3 The Arecibo dish sat in a natural sinkhole and could not be fully steered, so the target had to be whatever was conveniently positioned in the sky.3 M13 contains several hundred thousand stars.4
The message was broadcast at a frequency of 2,380 MHz with a 10 Hz bandwidth, using frequency-shift keying to encode ones and zeros.12 The bit rate was 10 bits per second, and the entire transmission took 169 seconds — just under three minutes.4 The transmitter operated at 450 kW.2 At that power and focus, the effective radiated energy made the Sun momentarily appear to be the brightest star in the Milky Way from the direction of transmission.4
Bernie Jackson, a heliophysicist then at Arecibo (later at the University of California, San Diego), programmed the message into the computer and pushed the button to begin the broadcast.3 Speakers outside the control room played an audio translation of the binary — two tones corresponding to 0 and 1 — so the assembled audience could hear the message leave Earth.3 By the time the transmission ended, its first bits were already near the orbit of Mars.3 The signal passed Pluto's orbit approximately 5 hours and 20 minutes after transmission.4
The 1,679 bits were chosen because 1,679 is a semiprime — the product of two primes, 23 and 73.2 A receiver who recognized this could arrange the bits into a 73-row by 23-column grid to produce a pictogram. The alternative arrangement (23 rows by 73 columns) produces no recognizable pattern.2
The message was designed primarily by Frank Drake, with contributions from Richard Isaacman, Linda May French, and James C. G. Walker, all at Cornell University or Arecibo. Carl Sagan and others also provided input.23
Read top to bottom, the pictogram encodes seven sections:2
Numbers 1 through 10 in binary, establishing the counting system used throughout the message.
The elements of DNA: the atomic numbers of hydrogen (1), carbon (6), nitrogen (7), oxygen (8), and phosphorus (15).
Nucleotide formulas: the molecular formulas of the sugar deoxyribose, phosphate groups, and the four nucleobases (adenine, thymine, cytosine, guanine) as they exist within DNA, expressed as counts of the five elements listed above.
The double helix and genome size: a graphic of the DNA double helix, with a binary number down the center representing approximately 4 billion nucleotide base pairs — the estimated size of the human genome in 1974.2 The actual count is now known to be approximately 3.2 billion.2
A human figure: a stick figure of a human, with the number 14 to its left. Multiplied by the transmission wavelength of 126 mm, this gives 1,764 mm (5 feet 9 inches), the average height of an adult male in the United States at the time.2 To the right of the figure, the number ~4.3 billion represents Earth's population in 1974.2
The Solar System: the Sun and all nine planets (Pluto was still classified as a planet), with Earth offset upward toward the human figure to indicate the message's origin. The relative sizes of the planets are roughly indicated but not to scale.2
The Arecibo telescope: a graphic of the dish, with the number 2,430 expressed in binary. Multiplied by the 126 mm wavelength, this gives the dish diameter of 306.18 m (1,004 feet 6 inches).2
The Arecibo message was not the first deliberate radio signal sent from Earth into space. In 1962, three Soviet scientists transmitted three words in Morse code — mir ("peace" or "world"), "Lenin," and "USSR" — using a planetary radar at Yevpatoria in Crimea.35 That transmission was bounced off Venus and returned to Earth; it never left the solar system and was not intended for an extraterrestrial audience.3
The Arecibo telescope continued operating for decades after the 1974 transmission. Its support cables deteriorated over the years, and on December 1, 2020, the 900-ton instrument platform suspended above the dish collapsed, destroying the telescope.3
As of 2024, the message has traveled approximately 50 light-years from Earth, a volume containing roughly 1,000 star systems.3 It will not reach M13 for another ~25,000 years, and a hypothetical reply would take at least 25,000 years more to return.2 By the time the signal arrives, the cluster's proper motion will have shifted its stars slightly, though most of the core will still be within the beam.2
In August 2001, a crop circle appeared in a field next to the Chilbolton radio telescope in Hampshire, England, arranged in a pattern resembling a modified version of the Arecibo message.2 It was 75 feet wide and 120 feet long. The formation has been attributed to human pranksters rather than extraterrestrial communication.2
The Arecibo message is a 1,679-bit interstellar radio transmission sent from the Arecibo Observatory in Puerto Rico on November 16, 1974, at 1700 GMT.1 It was directed at the globular cluster Messier 13 in the constellation Hercules, approximately 25,000 light-years from Earth.1 The transmission was a demonstration of the observatory's newly upgraded radio transmitter, not a serious attempt at interstellar communication.1
The message was transmitted during a ceremony marking the completion of a major renovation of the Arecibo telescope.3 The upgrades included a new aluminum surface for the 1,000-foot-wide (305 m) reflector dish and a high-power radio transmitter.3 Frank Drake, then director of the National Astronomy and Ionosphere Center, organized the ceremony and invited over 200 guests.3 U.S. Representative John Davis of Georgia gave the go-ahead for the transmission by paraphrasing a Daniel Webster quote that hangs in the House of Representatives.3
M13 was chosen as the target because it happened to be overhead at the time of the ceremony.3 The Arecibo dish sat in a natural sinkhole and could not be fully steered, so the target had to be whatever was conveniently positioned in the sky.3 M13 contains several hundred thousand stars.4
The message was broadcast at a frequency of 2,380 MHz with a 10 Hz bandwidth, using frequency-shift keying to encode ones and zeros.12 The bit rate was 10 bits per second, and the entire transmission took 169 seconds — just under three minutes.4 The transmitter operated at 450 kW.2 At that power and focus, the effective radiated energy made the Sun momentarily appear to be the brightest star in the Milky Way from the direction of transmission.4
Bernie Jackson, a heliophysicist then at Arecibo (later at the University of California, San Diego), programmed the message into the computer and pushed the button to begin the broadcast.3 Speakers outside the control room played an audio translation of the binary — two tones corresponding to 0 and 1 — so the assembled audience could hear the message leave Earth.3 By the time the transmission ended, its first bits were already near the orbit of Mars.3 The signal passed Pluto's orbit approximately 5 hours and 20 minutes after transmission.4
The 1,679 bits were chosen because 1,679 is a semiprime — the product of two primes, 23 and 73.2 A receiver who recognized this could arrange the bits into a 73-row by 23-column grid to produce a pictogram. The alternative arrangement (23 rows by 73 columns) produces no recognizable pattern.2
The message was designed primarily by Frank Drake, with contributions from Richard Isaacman, Linda May French, and James C. G. Walker, all at Cornell University or Arecibo. Carl Sagan and others also provided input.23
Read top to bottom, the pictogram encodes seven sections:2
Numbers 1 through 10 in binary, establishing the counting system used throughout the message.
The elements of DNA: the atomic numbers of hydrogen (1), carbon (6), nitrogen (7), oxygen (8), and phosphorus (15).
Nucleotide formulas: the molecular formulas of the sugar deoxyribose, phosphate groups, and the four nucleobases (adenine, thymine, cytosine, guanine) as they exist within DNA, expressed as counts of the five elements listed above.
The double helix and genome size: a graphic of the DNA double helix, with a binary number down the center representing approximately 4 billion nucleotide base pairs — the estimated size of the human genome in 1974.2 The actual count is now known to be approximately 3.2 billion.2
A human figure: a stick figure of a human, with the number 14 to its left. Multiplied by the transmission wavelength of 126 mm, this gives 1,764 mm (5 feet 9 inches), the average height of an adult male in the United States at the time.2 To the right of the figure, the number ~4.3 billion represents Earth's population in 1974.2
The Solar System: the Sun and all nine planets (Pluto was still classified as a planet), with Earth offset upward toward the human figure to indicate the message's origin. The relative sizes of the planets are roughly indicated but not to scale.2
The Arecibo telescope: a graphic of the dish, with the number 2,430 expressed in binary. Multiplied by the 126 mm wavelength, this gives the dish diameter of 306.18 m (1,004 feet 6 inches).2
The Arecibo message was not the first deliberate radio signal sent from Earth into space. In 1962, three Soviet scientists transmitted three words in Morse code — mir ("peace" or "world"), "Lenin," and "USSR" — using a planetary radar at Yevpatoria in Crimea.35 That transmission was bounced off Venus and returned to Earth; it never left the solar system and was not intended for an extraterrestrial audience.3
The Arecibo telescope continued operating for decades after the 1974 transmission. Its support cables deteriorated over the years, and on December 1, 2020, the 900-ton instrument platform suspended above the dish collapsed, destroying the telescope.3
As of 2024, the message has traveled approximately 50 light-years from Earth, a volume containing roughly 1,000 star systems.3 It will not reach M13 for another ~25,000 years, and a hypothetical reply would take at least 25,000 years more to return.2 By the time the signal arrives, the cluster's proper motion will have shifted its stars slightly, though most of the core will still be within the beam.2
In August 2001, a crop circle appeared in a field next to the Chilbolton radio telescope in Hampshire, England, arranged in a pattern resembling a modified version of the Arecibo message.2 It was 75 feet wide and 120 feet long. The formation has been attributed to human pranksters rather than extraterrestrial communication.2
