Austrian astronomer Joseph Johann Von Littrow proposed early in the 19th century that people should send a message to alien civilizations to let them know we are here.

He proposed to dig trenches configured in large geometric patterns in the Sahara Desert, fill them with kerosene and light them. His idea never came to fruition, but we haven't stopped our attempts to contact extraterrestrial life.

In 1962, the Soviet scientists directed a radio transmitter at Venus and saluted the planet in Morse code. The message was a test run for a new planetary radar to map objects in the solar system.

In 1974, a group of scientists transmitted a radio message toward Messier 13, a cluster of stars about 25,000 light-years away. The image was sent in binary code and depicted a human stick figure, a double-helix DNA structure, a carbon atom model, and a diagram of a telescope.