The plaque is based on measurements of the hydrogen atom. Hydrogen is the most prevalent element in the universe, and is often found in stars (such as our own sun.) At top left of the plaque are two hydrogen atoms in different states of energy. When hydrogen transitions to a higher energy state, it releases electromagnetic radiation at a wavelength of 21 centimeters.
The 21 centimeters was used as a unit of measurement to show human height, the Planetary Society said. At right, you can see figures of a man and a woman, who were posed in gestures to indicate welcome and that the human body is moveable and flexible. Beside the woman is the number 8 in binary code (which is commonly used in computers), with two ticks at the head and foot of the woman to represent her height. Her height is therefore 8 units high, or 8x21 centimeters = 168 centimeters (5.5 feet).
The large diagram at left shows the sun (at center) with a map to find it. Surrounding it are relative distances to pulsars, or very dense stars that rotate quickly and send out signals rapidly and regularly. At bottom you can see a map of our own solar system, with the sun (at left) and (from left to right) what were considered the nine planets in the 1960s: Mercury, Venus, Earth, Mars, Saturn, Jupiter, Uranus, Neptune and Pluto.
NASA maintained contact with the Pioneer 10 spacecraft until 2003, and Pioneer 11 until 1995. It is still in touch with the Voyager 1 and Voyager 2 spacecraft. In August 2012, Voyager 1 was the first spacecraft confirmed to cross the boundary to interstellar space, leaving the solar system behind forever.
WATCH: Peace Out, Voyager