Friday, October 12, 2012

APOD 1.7

This photograph is intriguing and very well executed. Star trails can be photographed using very long exposure times to document the movement of stars in the sky over long periods of time. This photographer documented the trails with 30 minutes worth of exposure, showing 7.5 degrees of rotation. The center of the circle, where the stars don't move much, is the North Celestial Pole with the circumpolar stars that are always above the horizon in the Northern Hemisphere where this picture was taken. It requires careful planning and a steady tripod to achieve a photograph like this one, which illustrates Earth's daily rotation in the solar system.

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