Wednesday, April 21, 1999 Published at 19:03 GMT 20:03 UK
Sundial bound for Mars
Designed to tell the time on Mars
By BBC News Online Science Editor Dr David Whitehouse
For the first time in history, humanity will send a sundial to another planet. Inscribed with the motto "Two Worlds, One Sun," the sundial will travel to Mars aboard Nasa's Mars Surveyor 2001 lander.
Images of the sundial, taken by the lander's panoramic camera after its landing on Mars in January 2002, will reveal the passage of the hours and seasons as the sun moves across the peach-coloured Martian sky.
In addition, the sundial's central black, grey, and white rings and corner colour tiles will act as a calibration target to adjust the brightness and tint of pictures taken by the camera.
"Our ancestors made astonishing discoveries about the nature of the heavens and our place in it by closely watching the motion of shadows," said US TV science show host Bill Nye, as he unveiled the sundial design at a press conference.
The sundial will be 3 inches (about 8 cm) square, and will weigh just over 2 ounces (60 g). Made of aluminium to minimise its weight, its metal surfaces will be black and gold.
The sundial's central black, grey and white calibration rings are arranged to represent the orbits of Mars and Earth, and red and blue dots show the positions of the planets at the time of the landing in 2002. Portions of the central shadow post are gold to represent the sun.
"The sundial carries a message for future Martian explorers who may seek it out, or who may find it by good fortune. The four gold side panels around the sundial's base are engraved with the words:
People launched this spacecraft from Earth in our year 2001. It arrived on Mars in 2002. We built its instruments to study the Martian environment and to look for signs of life. We used this post and these patterns to adjust our cameras and as a sundial to reckon the passage of time. The drawings and words represent the people of Earth. We sent this craft in peace to learn about Mars' past and about our future. To those who visit here, we wish a safe journey and the joy of discovery."
The sundial was designed in conjunction with the US National Science Teachers Association. Over 160 design concepts were submitted from children across the country.
One idea suggested by children was that the sundial bear writing in many languages, representing the diverse cultures of Earth.
Once the spacecraft lands on Mars and the exact orientation of the sundial can be determined, viewers will be able to tell local Martian time from sundial images and a computer-generated overlay posted on the World Wide Web.
Over the course of a day, viewers on Earth will thus see the passage of time on Mars recorded in the sweep of the shadow of the sundial's central post. The shadow will also reveal the changing Martian seasons over the full duration of the mission.