How many bits of data were in the Arecibo message?

The Arecibo message contained 1,679 bits of data. The number was deliberately chosen because it is the product of the two prime numbers 23 and 73, allowing the binary signal to be arranged as a rectangular image.

The message was transmitted once on November 16, 1974, from the Arecibo Observatory in Puerto Rico. It was aimed toward Messier 13, a globular cluster about 25,000 light-years away, primarily as a demonstration of the observatory’s capabilities rather than a practical conversation with extraterrestrials. At a transmission rate of 10 bits per second, the broadcast lasted less than three minutes.

When arranged in the intended 73-row by 23-column format, the bits form a pictorial message. Its sections encode the numbers one through ten, the atomic numbers of elements in DNA, a representation of DNA’s structure, a human figure and population estimate, the Solar System, and the Arecibo telescope. The number is often mistaken for a byte count: 1,679 bits equals roughly 210 bytes, so it is not 1,679 ordinary text characters.