A rainbow is one of the most beautiful natural phenomena that we can easily observe after heavy rain during the day.
The phenomenon of a rainbow is essentially the dispersion of sunlight when it refracts and reflects off raindrops. When mentioning rainbows, many people immediately think of the vibrant arc with seven prominent colors: red, orange, yellow, green, blue, indigo, and violet.
One thing that few people notice is that the colors of a rainbow follow a specific order: Red is always at the top, while violet is at the bottom. This is due to the way light is reflected by the raindrops. The higher raindrops tend to create the color red, while lower droplets refract blue. At different angles, a rainbow can take on certain shapes, giving us the impression that it is moving. The larger the raindrop, the more vivid the colors of the rainbow appear, and vice versa.
However, besides the common seven-colored rainbow, there is an extremely rare phenomenon known as “white rainbows” or “fog bows,” which many people jokingly refer to as “ghost rainbows.”
A white rainbow is created when sunlight shines through small water droplets in fog at the right angle.
A white rainbow appeared in Brookline, Massachusetts, USA, in September 2014. (Photo: Eileen Claffey).
According to Earth Sky, fog bows, or white rainbows, are created by the same mechanism as regular rainbows. Rainbows typically appear when the air is filled with raindrops, and you always see them opposite the sun. The white rainbow follows the same principle, always opposite the sun, but it forms from small water droplets in fog or clouds rather than larger raindrops.
White rainbows can be observed in thin fog when sunlight shines through. Because the water droplets in fog are very small, white rainbows only exhibit faint or colorless hues.
“Some white rainbows have very low contrast. If you want to observe a white rainbow, look for subtle changes in light in the fog. The sun needs to be at an angle of about 30-40°, or you must stand on a high hill where the fog and white rainbow can be seen from above. A white rainbow can be as large as a regular rainbow but much wider,” says Les Cowley, an expert at the Atmospheric Optics website.
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