We continue to listen out for alien civilisations, but a few projects have tried sending specific messages in the hope of attracting communication. As a technological civilisation, we’ve been sending inadvertent radio noise into space for over 100 years, but to communicate across the stars, radio signals need to be specifically focused and not random.
The first calling card to the stars was the Arecibo Message in 1974, sent towards a globular cluster of stars 25,000 light years away. It was designed by Search For Extraterrestrial Intelligence (SETI) Institute founder Frank Drake and astronomer Carl Sagan as a 210-byte message that can be assembled into a picture. It covered mathematics, DNA, the human form, the Solar System and Arecibo radio telescope.