Fogbows explained: how tiny droplets blur rainbow colors through diffraction

Overview

This video unpacks the phenomenon of fog bows, explaining how extremely small water droplets blur the vivid colors of a rainbow through diffraction and interference. It describes how droplet size shifts the light pattern and why fog bows resemble rainbows but lack color, while also highlighting browser based tools that help researchers organize information.

• Fog bows arise from diffraction by tiny droplets rather than simple reflection
• Smaller droplets broaden diffraction patterns, washing out color to white
• Diffraction patterns produce concentric color rings in normal rainbows and fade to white in fog
• The video also showcases Opera’s features for research and browsing efficiency

Introduction

The video examines fog bows, a type of rainbow formed in fog using the same underlying physics as regular rainbows but with much smaller droplets. Instead of a single bright arc with distinct colors, fog bows appear pale or colorless because diffraction from tiny droplets blurs the spectrum. The explanation builds from the basic idea that sunlight entering a raindrop or a fog droplet creates a range of reflected light angles, with blue and red light bending differently. In rain, this produces a crisp rainbow, while in fog the tiny droplets cause the colors to spread out and overlap, reducing the saturation of each color.

Workings of Rainbows and Fogbows

Rainbows form when sunlight interacts with water droplets and undergoes reflection and refraction inside the droplets. Different colors bend by different amounts, causing a spread into a spectrum. The video uses a familiar 42 degree and 40 degree geometry to illustrate red and blue light coming from drops at different angles. However light is a wave, so diffraction and interference begin to modify the simple picture. When light passes through a slit or scatters off a small object, waves from different parts of the aperture or object interfere, creating a diffraction pattern of bright and dark fringes. In the rain droplet, diffraction adds only a small correction because the drops are effectively wide compared to the light wavelength, so the rainbow remains vivid.

Diffraction and Droplet Size

As the video explains, diffractive effects depend on the droplet size. Normal rain droplets, being relatively large, produce diffraction patterns that are narrowly spaced and do not blur colors perceptibly. With smaller droplets, the diffraction peaks become broader and more widely spaced. This produces a sequence of inner rings for each color and can lead to supernumerary bows. When the droplets become very small, as in fog, the diffraction broadens so much that colors smear into one another and the resulting light resembles white sunlight rather than a saturated spectrum.

From Slits to Droplets

The explanation connects to the classic slit diffraction picture. Waves passing through or reflecting from different parts of an aperture interfere, producing a diffraction pattern. In the context of droplets, the droplet acts like a tiny obstacle with several reflecting surfaces, creating multiple bright angles corresponding to different colors. Narrower effective apertures (smaller droplets) broaden the diffraction pattern, expanding the set of angles from which light is strongly reinforced and thereby washing out color in the observed rainbow.

Concentric Rings and Color Blurring

For larger droplets, constructive interference happens at angles corresponding to red or blue light, yielding discrete color bands. When the droplets shrink to about a twentieth of a millimeter or smaller, these rings broaden and interleave so the colors bleed into one another, reducing saturation. In fog with droplets of a few hundredths of a millimeter, the diffraction is so broad that the rainbow appears pale or colorless, similar to how red, green and blue blur together when out of focus to produce white light.

Observation and Takeaways

The phenomenon is a vivid demonstration of wave optics in nature. It shows how the same physics that creates rainbow arcs also produces fog bows once the droplet size crosses a threshold. The video uses intuitive language and analogies to guide the viewer from the classic rainbow to the fog bow and explains why supernumerary bows vanish as droplets get smaller. It also hints at how researchers use photos and data slices to map the relationship between drop size and color distribution.

Conclusion

By linking droplet size to diffraction patterns, the video provides a cohesive picture of why fog bows look different from standard rainbows and how color can be blurred when light interacts with tiny droplets. The discussion closes by hinting at broader applications of diffraction in atmospheric optics and the way modern tools help scientists organize and explore complex data, including features that support image recognition and research workflows.