PASADENA, Calif., Dec. 24 (UPI) -- Identical sundials, each about 3-inches square, are being carried by the two roving vehicles, Spirit and Opportunity bound for Mars.

Bill Nye, who used to appear in the 1990s on PBS's "Bill Nye the Science Guy," has turned a age-old piece of calibration equipment into a state-of-the-art scientific instrument.

As Nye was looking over the designs for instruments to be carried to Mars, he noticed that the solar-panel calibration device for the lander's Pancam panoramic camera looked familiar.

"I said, 'Hey you guys, this has got to be a sundial. It'll be great.' They said, 'Bill, this is a space program. We have a lot of clocks. Thanks for your input.' Everybody was skeptical at first but later thought it would be kind of cool," Nye recalled.

Unlike ordinary sundials, the Mars sundials have no hour marks -- the rovers carrying them will be changing position frequently, rendering permanent hour lines meaningless, according to Nye. Instead, the rover science team will add hour marks electronically onto Pancam photos of the sundial.

One full day of the mission will be devoted to sundial observation.