Rainbows: From Science to Activism

By Brigette Smith, 2018 SPS Intern, USA

In 1978 Gilbert Baker created the first rainbow flag as a symbol for LGBT+ Pride. Baker wanted a flag that could be a symbol of the global LGBT+ community and he chose the rainbow because he believed the various colors were a good representation of the diversity in the community. Baker believed this natural and beautiful symbol had an undeniable power and was certain of the design from the very start. Each color on the flag stands for something: spirit, serenity, art, nature, sunlight, healing, life, and sex. He described the first time he raised the flag in the 1978 Gay Freedom Day Parade saying, “Raising it up and seeing it there blowing in the wind for everyone to see. It completely astounded me that people just got it, in an instant like a bolt of lightning – that this was their flag. It belonged to all of us. It was the most thrilling moment of my life. Because I knew right then that this was the most important thing I would ever do – that my whole life was going to be about the Rainbow Flag.” The rainbow, one of nature’s most magical optical phenomena, gained a new and meaningful purpose that day.
Rainbows have always been viewed as a very mystical occurrence in nature. Scientists and mathematicians were trying to explain them since Aristotle’s time. Before a correct explanation could be formed, some of the basic laws of light and optics had to be explained. The Greek mathematician Euclid was the first to correctly formulate the law of reflection, which states that light will travel in a straight line and reflect from a surface at the same angle at which it encounters the surface.
The Arabian mathematician and physicist Ibn Sahl is credited as the first to derive the law of refraction from his work on lenses. Refraction is the “bending” of light that occurs any time light changes speed as it passes from one medium into another. The law of refraction describes the relationship between the incidence angle and the refraction angle allowing us to determine the direction the light will travel after refraction occurs.
History has a hard time distinguishing the first to correctly explain the rainbow, all we can say for sure is that Kamal al-Din al-Farisi and Theodoric of Freiberg both gave correct mathematical explanations of the rainbow around the same time, working completely independently of each other. They found that, though it is a complex phenomenon, the rainbow could be explained by a few optical operations. 
“Light” usually refers to visible light or electromagnetic radiation that can be seen with the human eye. Light has wave-like behavior and the color the light appears depends on the frequency of the wave. On the low end of the spectrum of visible light, the light frequency is around 400 THz, which appears red; on the high end of the color spectrum, the wave’s frequency is around 700 THz, which appears violet. White light is actually a coalescence of the various colored light waves, and is the natural light that travels from the sun.

When white light interacts with water in the air in just the right way, a rainbow is formed. For this to occur the light must travel into the raindrop in such a way that the light reflects off the back of the raindrop and refracts as it is entering and exiting the raindrop. The amount of refraction that occurs is dependent on the frequency of the light. When white light enters the raindrop, the colors traveling at different frequencies will slow down at different rates and will begin to separate. Some of the light of each color will reflect off the back of the raindrop and travel out the front again, refracting as it re-enters the air. These refractions are what separate the colors of the rainbow for us to see.

We are only able to see the color reflecting from the raindrop that hits our eye. We are able to see all of the colors of a rainbow when light reflects off many raindrops. This is due to the geometry of optics. The light must be reflected at a specific angle for a rainbow to be visible. This angle varies slightly depending on the frequency of each color, but is commonly known as 42 degrees. The sunlight strikes the cloud of raindrops at approximately 42 degrees and the light is reflected at the same angle of deviation. When this condition is met, a circular band of colors is visible at an angle of 42 degrees to the central axis. An observer is really only able to see one color from each raindrop because of the angle the light will enter their eye, but because the angles depend slightly on the frequency the colors are stacked and a rainbow is visible with enough raindrops.

The science of rainbows may be a little complicated but what they symbolize today means so much more. Rainbows have become a symbol to represent love, self-acceptance, support, and solidarity. Baker himself said, “The flag is an action – it’s more than just the cloth and the stripes. When a person puts the Rainbow Flag on his car or his house, they’re not just flying a flag. They’re taking action.” The LGBT+ community still faces a lot of challenges and discrimination today. To raise awareness and visibility in the scientific community about LGBT+ issues today has been designated the very first LGBTSTEM Day. This is a celebration designed to support and strengthen the community of LGBT+ people in the STEM fields. July 5th was chosen because the date can be written as ‘507’ which is the wavelength (in nanometers) of green light or, in the United States, as ‘705’ which is the wavelength of red light. To learn more about LGBTSTEM Day visit Pride in STEM.

Written by: Brigette Smith

I am working with the outreach department of the Optical Society this summer through an internship program with the Society of Physics Students. I have a strong passion for work in STEM outreach and am very thankful to have this opportunity to work with such an amazing team.Stay tuned to learn more about the importance of diversity and inclusion in STEM and how to create a more inclusive professional environment!


Posted: 5 July 2018 by Brigette Smith, 2018 SPS Intern, USA | with 0 comments

The views expressed by guest contributors to the Discover OSA Blog are not those endorsed by The Optical Society.


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