Rainbows are optical phenomena that occur when sunlight is refracted, reflected, and dispersed by water droplets in the air. Each droplet acts like a tiny prism, splitting the light into its component colors. This results in the beautiful arc of red, orange, yellow, green, blue, indigo, and violet.
While we often marvel at the beauty of rainbows, understanding the science behind them allows us to appreciate them even more. A rainbow forms due to the interaction of sunlight with raindrops in the atmosphere. However, several intricate steps occur before the vivid spectrum of colors appears in the sky.
How Light Interacts with Water Droplets
When sunlight enters a raindrop, it slows down and bends—a process known as refraction. Since white light is composed of different wavelengths, each color bends at a slightly different angle. This separation of light into various colors is called dispersion.
After refraction, the light reflects off the inner surface of the raindrop and exits, bending once more as it moves from the denser water back into the air. The combination of refraction, reflection, and dispersion results in the circular arc of a rainbow.
Why Are Rainbows Arched?
Rainbows always appear in an arc because of the way light is refracted and reflected within raindrops. The angle at which light exits the droplet (usually around 42 degrees) determines the visible shape. From an observer’s perspective, the arc forms due to the limitation of our field of view on the ground. If viewed from an elevated position, such as an airplane, a rainbow can sometimes appear as a full circle.
The Colors of the Rainbow
The standard seven colors of a rainbow—red, orange, yellow, green, blue, indigo, and violet—are due to the varying wavelengths of light. Red, which has the longest wavelength, bends the least, while violet, with the shortest wavelength, bends the most. This difference in bending causes the colors to spread out in a predictable order.
Double and Supernumerary Rainbows
Occasionally, we see double rainbows, where a second, fainter rainbow appears outside the primary one. This occurs when light undergoes an additional reflection inside the raindrop before exiting. The secondary rainbow has its colors reversed, with red on the inner edge and violet on the outer edge.
Even more rare are supernumerary rainbows, which consist of additional faint bands inside the main rainbow. These arise due to wave interference when light waves overlap inside raindrops.
Rainbows and Optical Illusions
Rainbows are not physical objects but rather optical phenomena. This means no two people see the exact same rainbow. Each observer sees their own unique rainbow based on their position relative to the sunlight and raindrops.
Furthermore, rainbows do not exist at a specific location. If you try to move toward the end of a rainbow, it will always appear to shift further away, reinforcing the age-old myth of the unattainable pot of gold.
Conclusion
Rainbows are a perfect blend of physics and beauty. Their formation relies on the complex interplay of light, water, and the observer’s position. Whether a full circle viewed from the sky or a double arc spanning across the horizon, rainbows continue to captivate and inspire wonder in people around the world.