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.
2003 February 26 
Posted on 02/26/2003 5:43:11 AM PST by petuniasevan
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.
2003 February 26
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. 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 dinner near Horseshoe Canyon in Utah, the photographer chanced to find that an even more spectacular sight was occurring in the other direction just over the canyon -- a particularly vivid set of anticrepuscular rays.
A silvery bubble rises through Earth's atmosphere. Seen from Skylab, well above the Earth's dense atmosphere, the rising Moon is at first almost unrecognisable but for its surface markings. Moonlight enters the atmosphere and then leaves again, a path length twice that in moonrises seen from Earth's surface. The atmospheric lens pushes the lower limb upwards to create the highly flattened shape. Look out for a moonrise (or sunrise) from a high flying aircraft, the distortion is almost as extreme.
"O Lord my God, when I in awesome wonder", etc.
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