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14 FOUR SEASONS BREEZE | MAY 2021 "Understanding the Weather" – A Series by Mel Zeldin, Retired Meteorologist In recent months, there have been several local postings of beautiful photos taken just before sunrise by Four Seasons Beaumont residents. These feature red, orange, and yellow-colored clouds which make for beautiful skyscapes. But do you know the reason why these colors only occur during sunrises and sunsets, and also why the same phenomenon that produces these colors in the sky is the reason the sky is blue? It has to do with our atmosphere. Viewed in space, the sky would appear black and the sun white. The light coming from the sun as white is a combination of all the colors of the rainbow, from ultraviolet and blue on one end of the color spectrum and red at the other end. Each color has a different wavelength, with the ultraviolet and blue colors having the shorter wavelengths and the red and yellow colors longer wavelengths. As the sunlight passes through the atmosphere, it interacts with randomly located air molecules. That interaction causes shorter wavelengths to be scattered much more dominantly than the longer wavelength colors in a process called Rayleigh scattering. During the day, the shorter wavelength blue light is scattered in all directions by the air molecules, and our eyes pick up the blue light as coming from the sky. The scattering effect is akin to "painting" the sky blue. So, what happens at sunrise and sunset, and if there are clouds, why do we get those colorful red, orange, and yellow colors off the clouds? As the sun approaches the horizon, because of the angle of the sun, the sunlight has to pass through a greater amount of the atmosphere, as depicted in Figure 1. During the day, the shorter sunlight path through the atmosphere, while scattering the blue light, does not completely scatter all of the blue spectrum. But as the figure shows, toward sunset (and also sunrise), there is a greater amount of the atmosphere through which the sunlight travels, scattering out virtually all of the blue light, leaving the dominant longer wavelength colors of red, yellow, and orange to be visible. While the horizon tends to take a yellowish hue at sunrise and sunset, if there are clouds, especially higher-level clouds in the sky, the long-path sunlight passing through the atmosphere is reflecting off the base of the clouds, giving the clouds the red, yellow and orange colors, and natural beauty to the eye of the beholder. Often the most pronounced colors are seen shortly after the sun sets in the evening, and before the sun rises in the morning. 1: Depiction of the sunlight path through the atmosphere during the day (short path) and at sunset and sunrise (long path) 2: Blue skies over the snow-capped San Bernardino Mountains 3: Red-blazened clouds just before sunrise 4: A multi-colored sunset 5: Sunset over the Statue of Liberty 1 2 5 3 4 The Science of Stunning Skies

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