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Posts Tagged ‘crepuscular rays’

Crepuscular rays

In response to the image offered by Thomas, Ana’s students have worked on portraying crepuscular rays. These have the particular beauty of combining the curves of a convection cell with the disciplined lines of the light rays which, being the lines of a cast shadow, are perfectly straight.

Here are a few of the results, also available on her blog today:

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Oil pastels after Thomas's image of crepuscular rays

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Anticrepuscular rays

Ruth shares her discovery of a wonderful APOD image of anticrepuscular rays. A brief description is given at the APOD site, and also here on sept 12. It’s a wonderful image. Thanks, Ruth.

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Crepuscular rays

One of the loveliest of celestial displays is rays of sunlight and shadow coming dramatically from behind the late afternoon and early evening cumulus clouds, often after a storm. They are called crepuscular rays; crepuscular is Latin for twilight. Actually, true twilight is after sunset and before dusk, while this is before sunset, but the sun is low, and, hanging out behind a cumulus, it casts bright rays and long shadows across the sky.

My good friend Thomas sends this image:

Crepuscular rays and cumulus clouds from Thomas Sept 09

Crepuscular rays and cumulus clouds from Thomas Sept 09

I used to wonder why these rays are always so centered in the sky. Why don’t they come from the left or the right side of the sky?

The answer is, of course, that the impression of radiating lines is merely perspective: like railroad tracks, these shadows and rays of light are perfectly straight, but since they stretch into the distance a good 40 miles or more, they do seem to converge. The coolest thing is that if Thomas had turned around, he would likely have seen pale anti-crepuscular rays in the eastern sky. He might not have sent me the images anyway because they would have been so pale, but they do show that the rays extend entirely across the sky. Overhead, they are so broad that it is hard to follow them against the brightness of the sky, but on the other side where they converge again, you may often see them.

Watch for it next time, Thomas.

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