Sun Reflection off Clouds

April 15, 2006

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Provided and copyright by: Joel Balazuc
Summary authors & editors: Joel Balazuc; Jim Foster

During descent a flight to Frankfurt, German on February 12, 2006 (10:40 a.m. local time), I noticed a sharp oval of bright light outside the cabin window. I had never before witnessed this, and at first, I thought it was the reflection of the Sun off the fuselage of our commercial jet. However, it was actually a phenomenon called the subsun. Subsuns are caused by the reflection of the Sun off of the flat upper faces of horizontally aligned ice crystals (typically plate shaped) -- they act like tiny prisms. Subsuns are usually seen in association with clouds lying below the aircraft, as is the case on the above photo.

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