We are all familiar with the illuminating reds, pinks, yellows and oranges that grace us every day as the Sun meets the horizon. Many people are enthralled with a good sunrise and sunset, rushing to the beach or the top of a hill to catch one. Many people will go most of their lives in love with the colorful show and wonder what really causes the sky to light up with such vibrant colors.
The colors of a sunset or sunrise is an atmospheric phenomenon associated with light optics. In our atmosphere, air molecules are referred to as selective scatterers because they selectively scatter certain colors of the light spectrum. The scattering of light occurs when light hits the surface of an air molecule and bounces off it in all different directions. The visible light spectrum (light we can see with our naked eye) consists of wavelengths of red, orange, yellow, green, blue and violet with red having the largest wavelength and violet the smallest. Selective scatterers tend to scatter light waves of a shorter wavelength like blue, violet and green. During the day when the Sun is highest in the sky, visible light hits your eyes at a more direct angle and the light has less atmosphere to travel through. Here the Sun appears white as most of the light waves hit our eyes at the same intensity. When the Sun hits the horizon, there is much more atmosphere that the light travels through. As the light travels through that length of the atmosphere, most of the blue, violet and green light is scattered away. The red, orange and yellow light is the what makes it through and reaches our eyes. This is what would make the Sun appear orange and red.
There are also particles in the air that contribute to the color of the Sun at sunset. These particles have a larger diameter than air molecules, thereby scattering the larger wavelengths of light such as yellow. When the atmosphere is filled with more of these particles you can see a redder Sun. For example, salt particles and water molecules are responsible for red sunsets observed over water at a beach.
Sunsets and sunrises are just one of many of the incredible things we are blessed with on Earth. Knowing the science behind them only enhances our admiration. It also makes for a good conversation to have with a friend next time you find each other enjoying one.
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©2018 Meteorologist Alex Maynard