Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

April 28, 1999
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

A Sundial for Mars
Credit: W. Sullivan (U. Washington) et al., Mars Surveyor 2001, NASA

Explanation: When Mars Surveyor arrives at Mars in 2002, it will carry a sundial. Even though batteries and a solar array will power the Mars Surveyor Lander, the sundial has been included to allow a prominent public display of time. The sundial idea was the brainchild of Bill Nye the Science Guy, who noticed that a post originally used for camera calibration could be redesigned. Millennia ago, sundials were state-of-the-art timekeepers for humans on Earth. Since the Sun casts similar shadows on Mars and Earth, accurate calibration of the shadow placement on the Martian Sundial will tell a curious inspector of returned images both the time of day and the season.

Tomorrow's picture: New General Catalog

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
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& Michigan Tech. U.