February 21, 2012
You were born into motion: oceans turning, continents drifting, clouds forming, planets circling, galaxies wheeling through the dark.
Anticrepuscular Rays Over Wyoming
Birthday · February 21, 2012
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APOD published February 21, 2012. Credit: Nate Cassell. A publication-date match, not a photo taken on your date. Independent of NASA.
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. 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. Pictured above is a particularly striking set of anticrepuscular rays photographed last month near Cheyenne, Wyoming, USA.
Image credit: Nate Cassell