Since childhood, the sky has fascinated me. Something about its expansive reach and wholeness speaks to my mind, body, and soul. The many colors in the sky offer such an array of feelings and thoughts to contemplate. While observing the sky this week, I wondered what makes all the colors possible.
What Causes Color
Colors in the sky are determined by molecules in the air and the way these molecules interact or diffuse light, or electromagnetic radiation. Each color of light has a specific wavelength that makes it unique.
The wavelength also plays a part in how light is scattered, or diffused. Red light has longer wavelengths and is harder for molecules in the air to scatter. Blue light has shorter wavelengths and is easier for molecules to scatter.
Since blue light scatters easily, it often dominates the sky’s spectrum. This is why the sky often appears blue, unless clouds block the view.
There are different types of light scattering, and the type that causes blue light is called Rayleigh scattering. This type of light scattering is dependent upon light wavelength. The many oxygen and nitrogen molecules in the lower atmosphere easily scatter lower wavelength light like violet and blue. However, blue light is more easily detected by the human eye, so we see more blue than violet.
Red Sunrises and Sunsets
If blue light is so dominant, why do we see red in the sunrise and sunset?
The answer lies in the position of the sun in the sky. Since the sun is lower in the sky at sunrise and sunset, its light rays pass through more of the atmosphere. At this position, more blue light is scattered away, making room for the longer wavelengths of red and yellow light to reach your eyes.
The atmosphere contains many different molecules and thus has a variety of ways to scatter light from the sun. The scattering and collection of light rays creates the many color combinations we see at any given time. How our eyes translate this light and its colors also plays a part.
The cones in our eyes determine what colors we see and how intense the colors appear. Light hits the cones, stimulating a response sent through the optic nerve to the brain. The brain then processes the information and returns a correlating color.
So, the sky is more than just a collection of light and molecules. It is a haven for science and offers many examples of nature’s changes to stimulate thought, growth, and perspective.
Resources and Related Links
Blue skies – http://spaceplace.nasa.gov/blue-sky/en/
Cones – http://www.livescience.com/32559-why-do-we-see-in-color.html
Light – http://www.britannica.com/EBchecked/topic/340440/light
Light wavelengths – http://science-edu.larc.nasa.gov/EDDOCS/Wavelengths_for_Colors.html
Rayleigh scattering – http://www.livescience.com/32511-why-is-the-sky-blue.html
Red sunrise and sunset – http://earthsky.org/earth/sun-looks-on-horizon