What Causes Rainbows To Appear?


Rainbows are one of nature’s most beautiful and enchanting optical phenomena, captivating people of all ages and cultures. The appearance of a rainbow is a result of the interaction between sunlight, water droplets, and the observer’s position relative to the sunlight and droplets.

Refraction and Reflection of Light

When sunlight passes through the atmosphere and encounters water droplets in the air, the light undergoes refraction and reflection. Refraction occurs as the light enters the water droplet, bending or changing direction due to the change in medium. This bending of light causes the different colors of the spectrum to separate. This separation creates the distinctive arc shape of the rainbow that we see in the sky, with red on the outer part of the arc and violet on the inner part.

Dispersion of Light

As the sunlight is refracted, it is also dispersed into its component colors – red, orange, yellow, green, blue, indigo, and violet. Each color has a slightly different wavelength, resulting in the distinct bands of colors seen in a rainbow. The process of dispersion is responsible for the vibrant and varied colors that make up a rainbow. The angle at which light is refracted within the water droplet determines the size and shape of the rainbow, influencing how vivid and pronounced the colors appear to the observer.

Total Internal Reflection

After the light is dispersed and reflected inside the water droplet, it undergoes total internal reflection when it reaches the back surface of the droplet. This reflection causes the light to bounce back towards the front, contributing to the formation of a rainbow. The angle of incidence and reflection play a crucial role in determining the visibility and intensity of the rainbow. Total internal reflection is essential in creating the arc of the rainbow and ensuring that the colors are displayed in their full spectrum.

Observer’s Perspective

For a rainbow to be visible, the observer must be positioned with the sunlight at their back and the rain or water droplets in front of them. This specific alignment allows the dispersed and reflected light to reach the observer’s eyes, creating the colorful arc that we perceive as a rainbow. The size, shape, and intensity of the rainbow can vary based on the observer’s position and the environmental conditions. The observer plays a crucial role in the formation and experience of a rainbow, as their perspective and position impact how the rainbow is perceived.


In conclusion, the appearance of a rainbow is a complex interplay of refraction, reflection, dispersion, and the observer’s perspective. Understanding the science behind rainbows enhances our appreciation of this natural marvel and reminds us of the beauty and wonder present in our world. Rainbows serve as a reminder of the intricate processes at work in nature and the harmonious blending of light, water, and vision that create such a breathtaking sight for all to enjoy.

Vanessa Bergoff

Vanessa is originally from the Ukraine. She has been living in Florida for the last 10 years. She holds a Bachelor's degree in English from the University of Central Florida and a Master's degree in Technical Writing from the University of South Florida. She covers mostly health and health-related issues for the Scientific Origin.