Why some rainbows lose their color and turn white
In short: You might expect every rainbow to display the classic ROYGBIV spectrum. However, under specific conditions, the vibrant colors can smear together into a ghostly white arc. This phenomenon, known as a fogbow, reveals a complex interplay between light, water droplet size, and the physics of diffraction.
The difference between a standard rainbow and a fogbow lies primarily in the size of the water droplets involved. A typical rainbow requires large raindrops, measuring about 2 millimeters in diameter. At this size, the droplets are spherical enough to allow for a clean distribution of colors as light refracts—bending through the water—and reflects off the back of the drop.
In contrast, fogbows form in humid conditions where the water droplets are significantly smaller, measuring only about 0.05 millimeters. Because these droplets are so tiny, a second physical process called diffraction becomes dominant. While refraction bends light as it enters the water, diffraction occurs when light bends around the edges of the droplet. This diffraction spreads the individual colors in multiple directions simultaneously.
Because the colors are being smeared together by diffraction, they blend into a white hue rather than remaining distinct. While these arcs are often entirely white, they can occasionally display faint hints of red or violet. The first recorded sighting of a fogbow was made by Spanish explorer Antonio de Ulloa between 1737 and 1739 in modern-day Ecuador, where he described seeing a "whitish" arch alongside other optical halos.
To witness this, you need a specific setup: a low sun (morning or evening) behind you, a thin enough fog to let light through but thick enough to reflect it, and an angle of approximately 40 degrees between the droplet, the sun, and your eyes.
Opens the Intellect+ feed with this card first. Swipe up for the next one.
Sources
- Summary by Intellect · source: Why Some Rainbows Turn White
- Also: White rainbows are real—but very rare
To cite this card, link to https://intellectplus.co.uk/app/space-why-some-rainbows-turn-white.
How we source, check and correct cards: Editorial standards.
General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.
Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?
Related
More in Physics · More in Space · Latest · A–Z · All topics
