SUNDIAL.This instrument, which will be about half the size it appears here, will count out the hours on Mars and help a NASA lander's camera calibrate itself.

OK, it may not be the most sophisticated peice of equipment ever bound for the Red Planet, but a tiny sundial--described on April 21 at a Cornell University press conference--will play two important roles on board NASA's Mars Surveyor 2001 lander. In addition to charting Martian hours and seasons, the instrument, measuring only eight centimeters (three inches) square, will help calibrate the lander's sensitive camera, one of four instruments being developed for the Athena Precursor Experiment, or APEX.

The sundial's design incorporates gray, black and white rings, representing the orbits of Mars and Earth. Around the outer ring are the words "Two Worlds, One Sun." Red and blue dots mark the planets' relative positions at the time of the 2002 landing. It is these three rings, plus four corner color tiles, that the lander's panoramic camera, the Pancam, will focus on to adjust for brightness and tint. The photometric surfaces will be made from a special silicone rubber compound, whereas the rest will be coated with anodized metal. The sundial itself will be made of aluminium to keep its weight at a slight 60 grams (two ounces).

When the lander arrives on Mars, it will begin relaying images of the sundial's face to a site on the World Wide Web. Mirrors placed on the outer calibration ring will show the color of the Martian sky above the dial, and a computer-generated overlay on the Web page will interpret Mars's local time, based on the shadow cast by the dial's central post. This shadow, over time, will also indicate the passing of Martian seasons.

"Our ancestors made astonishing discoveries about the nature of the heavens and our place in it by closely watching the motion of shadows," said Bill Nye, television writer and host of the children's program Bill Nye, the Science Guy, at the design's debut. "Now, at the dawn of the next century, we can make observations of new shadows, this time on another planet."

In addition to Nye, the design team included Jon Lomberg, an artist and creative consultant to the Mauna Kea Center for Astronomy Education in Hawaii; Tyler Nordgren, artist and astronomer at the U.S. Naval Observatory; Woodruff Sullivan, sundial expert and astronomy professor at the University of Washington; Louis Friedman, executive director of the Planetary Society; Steven Squyres and Jim Bell, astronomers at Cornell; and scores of children across the U.S.

SIDE PANELS. The sundial's four edges feature children's stick-drawings representing Earth's people and a message of goodwill.

Indeed, over the past year, some 160 children contacted Sheri Klug, director of Arizona State University's Mars Education and Outreach Program, offering drawings and suggestions for the sundial's design. Many of the children's ideas were implemented: The face of the sundial will be engraved the the word for Mars in 22 languages, which together are spoken by 75 percent of Earth's population. Two ancient languages--Sumerian and Mayan--are also included because both cultures were fascinated by the Red Planet. And the sundial's side panels feature stick figures drawn by the children to represent Earth's people.

The panels bear this inscription: "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." And good eyesight.

Images: MISSION TO MARS, Cornell University