The Arecibo Message, Described
Claude (AI model by Anthropic; written 2026)
Sent 16 November 1974; described 2026

Cold Library · Open Stacks · S-008010 · https://coldlibrary.com/s/008010
Rights: Written by Claude for Cold Library and dedicated to the public domain under CC0 1.0. The facts it describes belong to everyone. Guidance, not legal advice.
Source: Facts checked against Wikipedia, 'Arecibo message', https://en.wikipedia.org/wiki/Arecibo_message (retrieved 2026-10-11)
Generated 2026-10-14 from https://coldlibrary.com/en/open-stacks/arecibo-message-described

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On 16 November 1974, at a ceremony marking the upgrading of the great radio dish at Arecibo, in Puerto Rico, the telescope was turned for a few minutes from listening to speaking. It sent one message, once, toward the globular cluster Messier 13, a ball of several hundred thousand stars about 25,000 light-years away. The transmission lasted less than three minutes. It was sent at 2,380 megahertz, with a power of about 450 kilowatts, by shifting the frequency of the beam up and down by 10 hertz: one tone for a one, another for a zero, ten bits each second.

There were 1,679 bits in all. The number was chosen with care. It can be made by multiplying only two prime numbers, 23 and 73, so a patient receiver who wonders how to lay the bits out in a rectangle has very few choices. Arranged as 73 rows of 23, the ones and zeros become a picture. Arranged the other way, they become noise.

The picture is read from the top down. First come the numbers one to ten, written in binary, so that the receiver learns how this message counts. Then five numbers: 1, 6, 7, 8 and 15, the atomic numbers of hydrogen, carbon, nitrogen, oxygen and phosphorus, the elements of DNA. Below them are the formulas for the sugar, the phosphate and the four bases from which DNA is built, and below those a twisting double strand with a long number running down its middle: the count of base pairs in a human genome, as it was estimated in 1974.

Then a figure of a human being. Beside it, a height, given as fourteen times the wavelength of the message itself, about 1.76 metres; on the other side, the number of people then living on Earth, a little over four billion. Under the figure is a row of shapes for the Sun and the nine planets counted in 1974, with the third planet lifted slightly toward the person standing above it. At the bottom is a drawing of the telescope that sent the message, with its width written underneath, again in wavelengths: about 306 metres.

The message was designed by Frank Drake and colleagues at Cornell University and the Arecibo Observatory, with help from Carl Sagan and others. It was meant less as a real attempt to begin a conversation than as a demonstration of what a radio telescope could do. Travelling at the speed of light, it will reach the region of Messier 13 in roughly twenty-five thousand years. The cluster will have moved a little in its orbit around the galaxy by then, but not far.

The telescope itself no longer stands. Its platform fell into the dish on 1 December 2020. The message it sent is still travelling, and will be for a very long time.