Sandra came in from retrieving the morning paper early today and exclaimed “Danny, come out. You have got to see this rainbow!” I quickly grabbed our camera and ran out to see what she was so excited about. She was standing out in the front yard and pointing toward the western sky. I looked and arching up above the oak trees was one of the most vivid and beautiful rainbows I have seen in quite a while. This was not expected because there were just a scattering of clouds across the sky with no rain in the forecast. Nevertheless it was a wonderful sight to behold.
The Size of a Rainbow is Relative to the Sun’s Angle
This rainbow had some beautiful qualities. The arc was quite steep (almost vertical at the base on the horizon) and the top of the rainbow was very high in the sky. It turns out that this is due to the fact that it appeared early in the morning. The Sun was near the horizon and the Sun’s visible light rays forming the rainbow were nearly horizontal. The arc of a rainbow that occurs at sunrise or sunset appears to be larger that one that occurs when the sun is higher in the sky. The apparent height of a rainbow decreases as the height of the sun in the sky increases. When the Sun exceeds an angle of 42 degrees above the horizon no rainbow can be seen by an observer on the ground.
Morning and Evening Rainbows
Also the composition of the sunlight that reaches earth at sunrise or sunset generally has more red hues and less blue hues. This is because of atmospheric scattering of the sunlight due to dust, smog, and water vapor in the air. It is more prominent in the mornings and evenings because the light passes through a longer stretch of atmosphere at those times than it does when the Sun is higher in the sky. This affected the color of our morning rainbow by emphasizing the bands on the red side and muting the bands on the blue side. You can see this emphasized even more by the color of the clouds in the photos. We were certainly the benefactor of these phenomena and I am grateful that Sandra observed this beautiful rainbow and called it to my attention. The affect of the Sun’s angle on rainbow geometry and color has been understood since the 1600’s. The phenomena is explained in more detail in this post on Rainbow Angles.
A Sight that Evokes Happiness
There is something about rainbows that makes most people feel good. A rainbow is an elegant and sweeping display of color across the sky. It is amazing to me how quickly nature can summon up the ingredients and conditions necessary to form the pallette of visible colors that we humans can see. Viewing a rainbow is a fleeting experience. After five minutes the rainbow quickly dissappeard as the Sun rose. I can certainly tell you that this sight put a smile on my face and gave me a great feeling of happiness.
The Science of Rainbows
The science of rainbows is fairly simple and is taught to most of us in elementary school. All it takes is the Sun shining across some water droplets suspended in the atmosphere. In order to see the rainbow, the viewer of course must be in the right place in relation to the Sun and the water vapor. The water droplets act like a huge prism and through refraction and dispersion of light, the droplets break the sunlight down into its component freqencies forming the band of colors of the rainbow. We commonly say that a rainbow is comprised of the colors Red, Orange, Yellow, Blue, Indigo, and Violet. Historically these component colors of a rainbow were first identified by Isaac Newton. In reality, a rainbow is a continuum of light frequencies that extends from the infrared to the ultra-violet frequencies and includes the entire band of frequencies that humans percieve as the colors of the rainbow.
With this post we are creating a new category called Nature’s Art. From time to time we will be posting many more articles to this category as there are an infinite number of instinces where Nature either inspires art or is a naturally occurring art form in and of itself.
The Wikipedia article on rainbows is very good. It describes the science of rainbows, the scientific history, and the cultural influence the rainbow has had.
There many websites that explain very effectively how rainbows work.
There is a very nice interactive app on the National Taiwon Normal University website that effectively demonstrates the physics of rainbows.
The Watching the World Wakeup blog has a good post called How a Rainbow Works which is worth looking at.
The site How Rainbows Happen explains all the physics concepts required to understand how rainbows happen.
This web page called Rainbow Physics explains very simply how a rainbow works. It was posted by a photographer and has some good rainbow photos. It is one part of a 5 part series on how to photograph rainbows.
This website has some Interesting Rainbow Facts .