Sky Oddities • Atmospheric Optics • Fog, Cloud & Shadow Phenomena
Fogbows are pale, ghostly rainbow-like arcs that form when sunlight shines through tiny fog droplets. Unlike ordinary rainbows, fogbows are usually white or faintly colored because the droplets are much smaller than raindrops.
TL;DR: What Is a Fogbow?
A fogbow is a white or faint rainbow-like arc created when sunlight interacts with tiny water droplets suspended in fog or mist. Because the droplets are so small, diffraction spreads the colors, producing a pale “ghost rainbow.”
The Ghost Rainbow of the Atmosphere
Imagine seeing a rainbow with almost no colors. Instead of a brilliant arc of red, orange, yellow, green and blue, you see a broad white bow floating silently in fog.
This unusual phenomenon is called a fogbow. Sailors once referred to them as “sea-dogs” or “white rainbows,” while modern observers often mistake them for cloud arches, halos or supernatural apparitions.
What Causes a Fogbow?
Fogbows form when sunlight shines through extremely small water droplets found in fog, mist or low cloud.
- Sunlight enters tiny droplets.
- Light is refracted and scattered.
- Diffraction becomes important because the droplets are so small.
- The colors spread and overlap.
- The resulting bow appears white or only faintly colored.
The same basic geometry that produces rainbows is present, but droplet size dramatically changes the appearance.
Why Are Fogbows White?
Ordinary rainbows form in relatively large raindrops. These droplets separate colors efficiently, creating vivid spectral bands.
Fog droplets are much smaller. As light passes through them, diffraction spreads the colors so broadly that they overlap. Instead of distinct color bands, the observer sees a pale white arc with only slight hints of color along the edges.
This is why fogbows are sometimes called white rainbows.
Best Conditions for Seeing a Fogbow
- Fog or mist: tiny droplets are required.
- Sun behind the observer: the bow forms opposite the Sun.
- Low Sun angle: morning and evening often work best.
- Uniform fog: consistent droplet sizes improve visibility.
- Open viewing area: coastlines, valleys and elevated viewpoints are ideal.
Where Are Fogbows Most Common?
Fogbows can appear almost anywhere fog occurs, but they are especially common in:
- Coastal fog banks
- Mountain valleys
- Sea mist
- Arctic and polar regions
- Cloud decks viewed from aircraft
- Waterfall mist zones
Fogbow vs Rainbow vs Glory
| Phenomenon | Appearance | Main Cause |
|---|---|---|
| Fogbow | Wide white arc | Tiny fog droplets and diffraction |
| Rainbow | Bright colored arc | Larger raindrops and refraction |
| Glory | Colored rings around shadow | Backscattering by tiny droplets |
| Brocken Spectre | Giant shadow on fog | Observer shadow projected onto mist |
Can Fogbows Form Complete Circles?
Yes. Like ordinary rainbows, fogbows are actually circles. From ground level, the lower portion is usually hidden by the horizon.
From aircraft, mountaintops or high viewpoints above the fog layer, observers may occasionally see a nearly complete circular fogbow.
Why Fogbows Look So Mysterious
Fogbows often emerge suddenly from dense mist with little or no visible color. Their pale appearance can make them look artificial, supernatural or otherworldly.
Combined with low visibility and quiet atmospheric conditions, they have inspired folklore, ghost stories and maritime legends for centuries.
Best 301 Redirect Target for Old Fogbow Articles
Use this pillar as the primary redirect destination for older Strange Sounds articles covering white rainbows, fog rainbows, sea fog bows, ghost rainbows, cloudbows and unusual pale atmospheric arcs.
Related Atmospheric Optics Guides
Fogbows FAQ
What is a fogbow?
A fogbow is a pale white rainbow-like arc formed when sunlight interacts with tiny fog droplets.
Why are fogbows white?
The droplets are so small that diffraction spreads and overlaps the colors, producing a white appearance.
Are fogbows rare?
They are uncommon compared to rainbows, but they occur regularly in coastal fog, mountain mist and low cloud conditions.
Can fogbows have color?
Yes. Subtle red and blue coloration may appear near the outer edges, but most fogbows look white.
Can a fogbow form over the ocean?
Yes. Sea fog is one of the most common environments for fogbow formation.
Is a fogbow the same as a glory?
No. A fogbow is a broad pale arc, while a glory appears as colored rings around a shadow.
