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An Illusion Caused by Perspective

25 Apr 2016, 07:01 UTC
An Illusion Caused by Perspective
(200 words excerpt, click title or image to see full post)

What’s wrong with this picture? The photo was taken shortly after sunset, so you’d expect some clouds to be in darkness. Others should still be illuminated. But the clouds still illuminated should be at a higher altitude, and the ones in darkness should be lower. The opposite seems to be happening here. What’s the explanation?
As the Sun sets in the west, the “shadow of the Earth” rises in the east climbing progressively higher into the sky. I did a short slideshow on that in my Jul 13, 2015 post. You can see how the lowest clouds are the first to go dark, followed by progressively higher clouds. The apparent contradiction in the photo above is a matter of perspective. It’s caused by the relative positions of my camera, the dark clouds, and the illuminated clouds.
Those dark clouds that seem to lie “above” the illuminated clouds are actually closer and lower — probably less than 8 km (5 miles) distant at an altitude of 3 km (10,000 feet). The illuminated clouds are maybe 80 km (50 miles) distant at an altitude of 15 km (50,000 feet). Click on the thumbnail below to see the geometry.

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