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.

2006 September 17
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Anticrepuscular Rays Over Florida
Credit & Copyright: Daniel Herron

Explanation: What's happening over the horizon? Although the scene may appear somehow supernatural, nothing more unusual is occurring than a setting Sun and some well placed clouds. Strangely, the actual sunset was occurring in the opposite direction from where the camera was pointing. Pictured above are anticrepuscular rays. To understand them, start by picturing common crepuscular rays that are seen any time that sunlight pours though scattered clouds. Now although sunlight indeed travels along straight lines, the projections of these lines onto the spherical sky are great circles. Therefore, the crepuscular rays from a setting (or rising) sun will appear to re-converge on the other side of the sky. At the anti-solar point 180 degrees around from the Sun, they are referred to as anticrepuscular rays. While enjoying the sunset after visiting NASA's Kennedy Space Center in Florida, the photographer chanced to find that an even more spectacular sight was occurring in the other direction just over the Atlantic Ocean -- a particularly vivid set of anticrepuscular rays.

Tomorrow's picture: dwarf planet eris

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