I remember one of the first times I saw a rainbow. I was four, and my parents and I were visiting my grandparents in Vermont. It was raining, and my dad wanted to go for a walk before dinner. We walked up and down the road, and on our way back, we saw an amazing rainbow. My dad told me that they were really special and that you don’t get to see them very often. Ever since then, rainbows have been one of my favorite things.
Obviously, when I was four years old, I did not know or really care how rainbows happened. As I got older, I had gained a very basic understanding. When it is sunny and rainy at the same time the sunlight does something cool and gets separated into its different colors. For this labor, I got to investigate and find out the actual physics behind this phenomenon. What I want to know is: Why do rainbows not happen during all rain showers? Why do they look like arcs? and How do double rainbows happen?
The article The mathematical physics of rainbows and glories says: “The rainbow is one of the most beautiful phenomena in nature. It has inspired art and mythology in all people, and it has been a pleasure and challenge to the mathematical physicists of four centuries…. I hope that the following report, though it has to be concise and must leave out most of the history, will to some extent demonstrate this mathematical beauty.” I disagree with this. I feel as though my appreciation for the beauty and the mythology of a rainbow is the driving force behind my desire to research the science behind it.
Rainbows happen when falling raindrops separate white light into its seven colors into one concentrated band through a process called refraction (the bending of light). According to Tom Field of Photo Centric.com, the light refracts as soon as it enters the raindrop at a point called the water/air boundary. The light goes through the drop and reflects and magnifies against the interior wall of the drop. The amount of bending that occurs depends on the color of the light. Red light bends the least because it has the lowest frequency/ highest wavelength which allows it to move quickly through the water. While blue light bends a lot because of its higher frequency/lower wavelength. Rainbows cannot occur in rain showers at night or with a lot of cloud cover because there has to be a significant amount of sunlight to shine through the water drops
The most common type of rainbows that we see, primary rainbows or first-order rainbows, only involve one reflection. In this example, the light is reflected once on the interior surface of the drop, and it exits the raindrop towards the viewer. In second-order rainbows, which appear directly outside of the primary rainbow and have reversed order of colors, the light is reflected twice on the interior surface before it exits.
In order for a drop to be able to make a first-order rainbow, it must be approximately 42 degrees from the antisolar point which is directly opposite the Sun’s position relative to you. For a second-order rainbow, the drops must be about 51 degrees from the antisolar point. Rainbows are not a specific distance away from you so you cannot walk to the end of one. When you find the proper angle, any drops along that line, regardless of distance, can contribute to making the rainbow you see. It is also because of these angles that rainbows only occur in the early mornings and late afternoons. Towards the middle of the day, the antisolar point would be too far below the horizon.
Field, Tom. ”Rainbow Physics: How Rainbows Form (Photography).“ Www.PhotoCentric.Net. 20
Aug. 2011. Web. 27 Oct. 2011. This site focused on the reflection and refraction part of rainbow formation. It did a great
job of explaining exactly what goes on inside a raindrop starting from when the light goes in as
white light to when it comes out separated into all the colors. This appears to be a very
reliable source because it is current, it is a “dot org”, and it identifies the author. I used
this source to better my explanation of reflection and refraction. It helped me understand where
in the drop each process takes place.
This site actually had nothing to do with the rainbows that we see in the sky. It is all about the process of refraction in prisms. It explains why red light bends less than blue light. It may not be the most reliable source because it is a “.com” and it does not specify an author. However, it is current, and the information seems to be legitimate. The source was hugely helpful because it allowed me to understand why red light does not bend as much as blue light which is such an important building-block of a rainbow. I found this source last. I searched it out specifically because I felt that the bending colored light was a gap in my understanding.
John A. Adam, The mathematical physics of rainbows and glories, Physics Reports, Volume 356, Issues 4-5, January 2002, Pages 229-365, ISSN 0370-1573, 10. 1016/S0370-1573(01)00076-X.
This was an extremely long article. It answered all the questions for this labor in the first few paragraphs and went on for about 100 more. It is a very reliable source because it does come from a peer-reviewed journal. It gave me a very in depth description that helped my understanding. What I found the most helpful was the scientist’s perspective on rainbows. They said that in order to study the science behind rainbows, you have to leave out the mythological history of them and not look at them as a magical phenomenon. It was a helpful source because I used the information to elaborate on the first versus second order rainbows. I also liked that I was able to include an expert’s opinion about their importance.