Colors of the Rainbow

Sir Isaac Newton initially identified seven colors of the rainbow: red, orange, yellow, green, blue, indigo, and violet. However, in contemporary conventions, the commonly acknowledged list tends to simplify, leaving out indigo and recognizing six colors: red, orange, yellow, green, blue, and violet. Alternatively, a more modern interpretation introduces cyan, broadening the color spectrum to seven: red, orange, yellow, green, cyan, blue, and violet. his change reflects our evolving understanding of the rainbow’s chromatic composition.

What is a Rainbow?

A rainbow is a fascinating display of colors seen in the sky when sunlight interacts with water droplets, creating a beautiful spectrum. This happens because sunlight undergoes refraction, reflection, and dispersion within water droplets, forming a semi-circular arc. It’s important to note that a rainbow isn’t an actual object but rather an optical illusion influenced by the viewer’s position and the direction of sunlight or other light sources. While the most common rainbow is produced when sunlight strikes raindrops at a 42-degree angle, it can also appear in fog, sea spray, or near waterfalls.

In scientific terms;

• A rainbow is an optical phenomenon observed opposite to the Sun’s direction.
• The colors in a rainbow result from the refraction and internal reflection of light within water droplets.
• Each color is bent at a slightly different angle, leading to the separation of colors in the spectrum.
• The primary rainbow is formed by one internal reflection within water droplets, displaying colors in a specific sequence: violet, indigo, blue, green, yellow, orange, and red.
• Occasionally, a less intense secondary rainbow with a reversed color sequence is observed outside the primary bow.
• Higher-order rainbows, with multiple internal reflections, are rare and faint.
• Supernumerary rainbows, characterized by faintly colored rings inside the primary bow, arise from interference effects on light rays after one internal reflection.

Colors of the Rainbow

While many still believe in the seven-color rainbow, a closer look reveals more than just seven distinct hues. In reality, a rainbow is a mix of various spectral colors blending together.

The typical sequence for primary rainbows goes from:

• Red: with the longest wavelength (around 780 nm)
• Violet: having the shortest wavelength in the sequence (380 nm)

Even though we often remember seven colors in a rainbow, it’s essential to recognize that there’s a broad range of colors beyond these well-known ones. The magical display of a rainbow involves a multitude of colors, creating a captivating spectrum beyond the traditional seven.

Newton’s Color List

Sir Isaac Newton originally identified 7 colors of the rainbow, listed in order from top to bottom as Red, Orange, Yellow, Green, Blue, Indigo, and Violet. The acronym “VIBGYOR” is a handy mnemonic to recall this color order from back. However, Newton’s list has encountered criticism for two main reasons. Firstly, the human eye struggles to distinguish indigo from blue or violet effectively. Secondly, indigo is considered a tertiary color, making its inclusion in the list questionable. Primary colors are red, blue, and yellow, while secondary colors, achieved by mixing two primary colors, are orange, green, and purple. Tertiary colors, including indigo, result from further color mixing.

Modern 7-Color Rainbow

A contemporary approach to categorizing the rainbow’s colors draws inspiration from the color wheel, presenting Red, Orange, Yellow, Green, Cyan, Blue, and Violet. Cyan, akin to indigo, is a tertiary color, making this list neither superior nor inferior to Newton’s original classification.

Rainbow Variations

Glow: The radiant phenomenon known as the “glow” occurs opposite a rainbow, facing the sun, during rain or drizzle. This zero-order glow is created by light passing through raindrops, adding a mesmerizing aura to the atmosphere.

Double Rainbow: Witnessing a “double rainbow” involves a faint, secondary rainbow appearing above the primary one. This captivating display is a result of light reflecting twice inside raindrops, reversing the spectrum in the secondary rainbow.

Higher-Order Rainbows: Rainbows come in various orders, reflecting light at different angles within raindrops. From tertiary to quaternary rainbows, each order denotes the number of reflections. Tertiary and quaternary rainbows face the sun, with increasing faintness and broadness.

Twinned Rainbow: A “twinned rainbow” showcases two distinct rainbows originating from a single endpoint. This phenomenon arises when light encounters an air mass with diverse sizes and shapes of water droplets.

Supernumerary Rainbow: Thin and pastel-colored, a “supernumerary rainbow” appears below the inner arch of a rainbow. Constructive and destructive interference of light rays in an air mass with small, similarly sized water droplets produces these delicate hues and narrower bands.

Reflection Rainbow: Above bodies of water, a “reflection rainbow” emerges as a primary rainbow is reflected by the water. Unlike mirroring, it often stretches above the primary rainbow.

Reflected Rainbow: Directly on the water’s surface, a “reflected rainbow” forms as light is reflected by the water surface after passing through water droplets. Although not forming a circle, their endpoints create an almond-shaped formation.

Red Rainbow: Appearing at sunrise or sunset, a “red rainbow” or monochrome rainbow showcases long-wavelength red colors. This unique phenomenon results from sunlight traveling further in the atmosphere, scattering shorter wavelengths.

Fogbow: Similar to a primary rainbow, a “fogbow” is formed by refracted and reflected light in fog. However, due to smaller water droplets, fogbows often appear fainter and may exhibit few detectable colors.

Moonbow: A “moonbow” or lunar rainbow is produced by light reflected by the moon, which reflects sunlight and other celestial light. Dimmer than rainbows, moonbows offer a mystical display illuminated by moonlight.

Discovery of Rainbow

• Around 350 BC, the brilliant mind of Greek philosopher Aristotle sparked contemplation on rainbows. Later, Roman philosopher Seneca the Younger, circa 65 AD, expanded on these ideas, anticipating Newton’s prism discovery.
• Over time, thinkers explored rainbows’ appearances beyond the sky. The essential ingredients for vivid color displays were identified as water droplets and sunlight.
• Isaac Newton’s prism experiment in dissecting light unraveled the secret of the rainbow’s color spectrum, solidifying centuries of pondering
• Newton, noting an unchanging color sequence, introduced the concept of seven colors: red, orange, yellow, green, blue, indigo, and violet (ROYGBIV). Aligning with musical notes, he added orange and indigo, even though he initially saw five colors.
• Contemporary definitions often omit indigo from the visible light spectrum. Yet, Newton’s foundational work remains integral, offering a technical gateway to understanding the timeless allure of rainbows.

Scientific Insights into Rainbow Formation

Rainbows, captivating meteorological phenomena, are the result of intricate interactions between sunlight and atmospheric water droplets. Delving into the technicalities of their formation unveils a fascinating process:

Light-Water Interaction: The genesis of a rainbow lies in the encounter between sunlight and suspended water droplets. These droplets act as optical elements, mimicking prisms in their ability to disperse light.

Refraction and Dispersion: As sunlight infiltrates a water droplet, refraction at the air-water boundary occurs, causing the light to disperse into its spectral components. This dispersion is a consequence of varying refractive indices for different wavelengths, resulting in the distinct colors of the spectrum.

Intricacies Inside the Droplet: Once inside the droplet, the refracted light undergoes reflection at the droplet’s surface. Subsequently, it traverses the droplet, undergoing another refraction before emerging. This intricate dance inside the droplet contributes to the vibrant spectrum observed in a rainbow.

Seven Colors Symphony: The visible colors in a rainbow – red, orange, yellow, green, blue, indigo, and violet – are a manifestation of the intricate interplay between sunlight and water droplets. Each color corresponds to a specific wavelength, emphasizing the precision in this natural phenomenon.

Angular Precision of Rainbows: The angles at which rainbows are observed are not arbitrary but intricately linked to the physics of light. When the sun is positioned directly behind the observer, the main rainbow becomes perceptible at an angle of approximately 40 degrees from the horizon. Additionally, a secondary, less pronounced rainbow appears at about 53 degrees.

In essence, the allure of rainbows transcends mere aesthetics, offering a profound insight into the principles of light, refraction, and dispersion. The skies, it seems, are a canvas painted with the brushes of physics

Video on Colors of the Rainbow

References

• https://scijinks.gov/rainbow/#:~:text=A%20rainbow%20is%20caused%20by,component%20wavelengths%2D%2Dor%20colors.
• https://studiousguy.com/science-behind-the-rainbow/
• https://www.geeksforgeeks.org/7-colours-of-the-rainbow-vibgyor/
• https://www.britannica.com/science/rainbow-atmospheric-phenomenon
• https://education.nationalgeographic.org/resource/rainbow/
• https://www.metoffice.gov.uk/weather/learn-about/weather/optical-effects/rainbows/colours-of-the-rainbow
• https://www.splashlearn.com/blog/the-magic-of-rainbows-rainbow-colors-order-more/
• https://sciencenotes.org/colors-of-the-rainbow-in-order/