The Star Garden
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The two circles at the top of the plaque represent a hydrogen atom undergoing a change in the spin state of its electron. This produces a specific wavelength of 21 cm and a frequency of 1420 MHz, these units are used to provide a scale.
The right side of the plaque contains the image of a naked man and woman in front of one of the Pioneer probes. They are all drawn to the same scale so that the size of the people can be deduced by measuring the probe. The binary representation of the number eight is given on the far right, this, multiplied by 21 cm, gives the height of the woman. The man's hand is raised as if to say 'hello', although this would probably not be understood by aliens, it does illustrate our opposable thumbs. These images drew a number of complaints, some argued that the figures looked too Caucasian. Some did not think people should be depicted naked but others did not think the images were explicit enough, showing male but not female genitalia. It is rumoured that the image was censored for NASA's approval but Sagan stated that this was a stylistic decision, the people are modelled on Greek sculptures.
The shape on the left shows fifteen lines originating from a single origin, the line to the right which extends behind the human figures represents the Sun's distance from the centre of the Galaxy. The fourteen other lines represent pulsars which are used as reference markers. The marks on the lines give the periods of the pulsars in binary code using the frequency of the hydrogen spin change as a reference unit. These periods change with time and so this information could be used to determine where and when the probe was launched. The lengths of the lines represent the relative distances to the Sun.
The bottom of the image shows the Solar System with the trajectory of the Pioneer 10 spacecraft depicted. The distance of the planets from the Sun in multiples of Mercury's orbital distance are given in binary next to each planet. Pluto is depicted as it was considered a planet until 2006.
Voyager 1 and 2
The Voyager 1 and 2 probes were launched in 1977 in order to study Jupiter and Saturn, although Voyager 2 travelled past Uranus in 1986 and Neptune in 1989. In 1990, Voyager 1 took the first photograph of all the planets in the Solar System as well as the famous 'pale blue dot' image which shows the Earth from six billion kilometres away.
Both probes are expected to keep transmitting signals back to Earth until at least 2025 and Voyager 1 is currently the furthest man-mad object from Earth. The Voyager probes are both travelling in the general direction of Pioneer 11.
Location and trajectories of spacecrafts as of 2007 Image credit: Wiki Commons
Each of the Voyager probes contain a gold-plated copper record. The cover contains an isotope of uranium which could be used to work out when the probe was sent. It is etched with the image of the hydrogen atom and pulsar map used in the Pioneer probes. The top left shows the image of a record player with the speed to turn it given in binary using the hydrogen atom for reference. The top right shows how to view the video portion of the record.
The record itself contains recording of sounds and images representing the diversity of life and culture on Earth. The contents were selected by a NASA committee chaired by Sagan. Sagan attempted to represent a mixture of cultures and, at the insistence of his third wife Ann Druyan, he included the music of Chuck Berry along with a number of classical composers and an hour long recording of Druyan's brainwaves. Sagan was not permitted to include naked anatomical drawings and so used silhouettes to represent the human body.
Examples of images included on the Voyager Golden Record
References
See NASA's profiles of Pioneer 10 and 11 and Voyager 1 and 2.
Pioneer and Voyager (1900s)
Pioneer 10 and 11
The Pioneer 10 and 11 probes were launched by NASA in 1972 and 1973 in order to study Solar winds and cosmic rays as they travel through the Solar System. Pioneer 10 was the first spacecraft to travel through the asteroid belt in 1972 and the first to observe Jupiter in 1973. It is currently moving away from the center of the Galaxy in the direction of the Taurus constellation, although NASA lost contact with it in 2003.
Pioneer 11 reached Jupiter in 1974 and was the first probe to reach Saturn, five years later. It left on a trajectory which will take it out of the Solar System. It is currently moving in the opposite direction to Pioneer 10, towards the constellation Scutum and the centre of the Galaxy. NASA lost contact with Pioneer 11 in 1995.
English journalist Eric Burgess was the first to suggest that the Pioneer probes should contain a message from mankind. He approached American physicist Carl Sagan with the idea, who took it to NASA. NASA agreed, giving Sagan three weeks to design the message. Sagan enlisted the help of fellow American astronomer Frank Drake and they designed a picture to be engraved on two twenty three centimetre wide aluminium plaques. Sagan's second wife Linda Salzman Sagan provided the artwork.