The Week in SpaceSeptember 20-26, 2010
Delicate Dance of Shadows Every six months the Earth’s axis of rotation is neither pointing toward the Sun nor away from it. At these times of equinox, or equal night, the Sun appears directly overhead at the equator at local noon, and days and nights there are exactly twelve hours long. Because Saturn takes much longer to orbit the Sun, an equinox there occurs about every fifteen years, but when it does, it sets the stage for a memorable play of light and dark as the shadows cast by Saturn’s moon fall directly on the planet’s rings. In April 2009, four months before Saturn’s equinox, the Cassini spacecraft captured this rare image. The shadow of its moon Tethys falls across the A ring and Cassini Division in this view, which looks toward the unilluminated side of the rings from about 50° above the ringplane. Image credit: NASA / JPL / Space Science Institute Weekly CalendarSeptember 20-26, 2010Holidays - Sky Events - Space History
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