After summer rain showers, a magnificent rainbow often appears in the sky, showcasing seven vibrant colors: red, orange, yellow, green, blue, indigo, and violet. This natural phenomenon is created by sunlight refracting through water droplets.
In summer, the duration of rain showers is usually brief and their coverage limited, allowing sunlight to break through almost immediately after the rain. At this time, the atmosphere is still filled with water droplets, and occasionally, light rain may still persist. When sunlight is refracted and reflected by these water droplets, a brilliant seven-colored rainbow emerges against the sky.
In winter, the weather turns cold and the air becomes very dry, making rain showers rare. As a result, the conditions necessary for rainbow formation are often absent.
Why is a rainbow arc-shaped?
According to the laws of physics, a light ray passing through a water droplet is redirected due to the refractive properties of water. It then reflects off the inner surface of the droplet and refracts again as it exits. An angle of approximately 42 degrees is formed between the incoming and outgoing rays. Sunlight comprises rays with varying wavelengths, which separate as they pass through the droplet. The degree of refraction varies slightly for each wavelength. The violet ray exits the droplet at about 40 degrees, while the red ray exits at approximately 42 degrees.
To see a rainbow, the rays of light reflected from the water droplet must reach the observer’s eye. The eye cannot capture all the reflected rays from a single droplet, but it can perceive the blue rays from several droplets, the red rays from others, and so forth.
The water droplets that reflect red rays back to the observer’s eye are positioned on a cone where the apex is the observer’s location, and the axis is a straight line passing through the eye and parallel to the direction of sunlight. The slope of this cone corresponds to the angle at which the rays reflect off the water droplets (42 degrees). The same principle applies to other colors. Thus, the observer will see colored bands arranged in order from outside to inside (from larger to smaller reflection angles) as follows: red, orange, yellow, green, blue, indigo, and violet, especially when viewed from an airplane or at a certain altitude.
Read more: “Discovering the Origins of the Rainbow”
