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| River in the Sky Captured by Matthew Shepherd at Troy, New York. The wavy orange line is an image of the nearby Mohawk River projected by a low sun onto the underside of the clouds. All images ©Matthew Shepherd, shown with permission |
Calm water on the river reflects parallel sun rays back upwards. They impinge on the cloud underside to form an image of the river. |
Arctic dwellers and explorers used to use a similar effect, an "Ice Blink". Distant leads, clear water separating ice floes, were imaged onto the undersides of clouds near the horizon. |
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| The sun was 5.5° high and the illuminated cloud patches 6-10° above the horizon. The distances of the reflecting parts of the river are less easy to judge but 7-15km likely brackets them. That gives a cloud underside height of very approximately 4-9000 ft. Not unrealistic for low level clouds. |