Museum of Time
rayon blue (blue flash)
 
The blue flash is a rare optical phenomenon that for thousands of years was only known to mountain people until Jules Verne romantically described a similar effect in his novel "Le Rayon Vert" (1882).

In that book a young woman in desperate need of a lover travels to the Atlantic west coast of Schotland to see the last rays of sunset over the ocean.
According to local folklore these last rays should be "of a green color; more beautiful than any other color ever found in nature and those who see it will never anymore make mistakes in emotional matters, because they can see clearly inside their own heart and the hearts of others.
At that time astronomers had never heard of green sunsets or sunrises but sailors and fishermen had seen them often while mountaineers described the first and last sunrays as blue.Egyptologists even remembered that the sun of the Faraos was met at sunset by a mythical green sun that during the night travelled through the World of the Death.
 
The famous British physicist Lord Kelvin wanted to see it with his own eyes and in 1899 he visited the Alps from where he indeed one August morning saw a blue sunrise near the Mont Blanc.
He explained the effect as a prismatic refraction of sunlight that gets stronger when the sun is close to the horizon. Because of this refraction the blue and green sunrays appear higher than the yellow and red sunrays.
At sea level blue sunlight is filtered away by dust and moisture but in the mountains the atmosphere is often so clear that the blue sunrays are seen first at sunrise. This only lasts for a second at most; after that the rest of sunlight shines like burning fire.
( Photographs taken from the AstroQueyras observatory in the French Alps, with view of the Mont Viso and Pain de Sucre mountains )
 
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