Encoding and Decoding the Arecibo 1974 SETI Message
The reason for this article is, in fact, sad. The world-famous radio telescope of the Arecibo Observatory in Puerto Rico has collapsed and is beyond repair. With a 304-meter in diameter, it was the largest radio telescope in the world for many years, with the help of which many discoveries were made. On this Wikipedia image, it is still in working condition:
But this article is about another event. In 1974, a message to extraterrestrial civilizations was sent into space from this telescope. How it was encoded, let’s figure it out.
Encoding
First, it’s interesting to understand how the message was made. As we know, the message size was only 1679 bits (approximately 210 bytes), and it was transmitted at a 2380 MHz frequency using a power of 450 kW. Frequency modulation with 10 bit/s speed was used for transmission. The number 1679 was specially chosen — it is the product of two prime numbers 23 and 73, so there is only one way to draw the picture in the form of a rectangle.
I could not find this message in WAV format, but it was easy to find it in binary form, and using Python we can easily generate the sound. Those wishing to listen to what the aliens will hear can download and run the code below. Background noise has also been added to the message to make it more realistic:
