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Chapter 4: Psychology

The Arecibo Message

Dear Dr. SETI:
I've seen once a picture of a signal that has been broadcast by the SETI people (I think) which showed, very roughly, the human morphology, the solar system, the DNA and other things, like a black-and-white assembly of some 50x50 pixel (no actual idea). Do you know where I could find this? I'd be thankful!

RS, Switzerland

The Doctor Responds:
Your general information is correct. The Arecibo Interstellar Message was transmitted on 16 November 1974 on 2380 MHz, toward the globular cluster M13, 25 kLY distant. It consisted of 1679 bits, to be arranged in 73 rows by 23 columns (those both being prime numbers). It graphically described a binary number sequence, hydrocarbon chemistry, DNA, the human figure (including a height scale), our solar system, and the Arecibo dish transmitting the signal. A very detailed image of this transmission, with complete description, may be found on page 290 of Carl Sagan's 1980 book "Cosmos." A depiction of the Arecibo Message, with additional descriptive material, may also be found on the Web, at

The transmission of this message was somewhat controversial. Some of the concerns regarding transmitting from Earth were discussed previously in this column.

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