A fogbow is a rare optical illusion that appears as a white arch in foggy conditions, often mistaken for a rainbow but far less common. Unlike the vibrant colors of a rainbow, a fogbow is mostly white because the water droplets in fog are much smaller, causing light to refract and reflect with less color separation. This phenomenon is especially tricky to spot in Australia, requiring the perfect alignment of sun, fog, and observer.
What Exactly Is a Fogbow?
A fogbow, also known as a mistbow, forms when sunlight (or moonlight) shines from behind you onto a layer of fog ahead. The tiny water droplets in the fog bend and reflect the light back toward your eyes, creating a pale, ghostly arc. Senior meteorologist Ilana Cherny of the Bureau of Meteorology explains that the fog must be just right—dense enough for refraction to occur but not so thick that it blocks the light.
Get the #1 Wireless Door Camera
REOLINK Bestseller: 2K Weatherproof Video Doorbell, No Monthly Fees.
Fogbow vs. Rainbow: A Comparison
| Feature | Fogbow | Rainbow |
|---|---|---|
| Color | Mostly white with faint pastel edges | Full spectrum of vibrant colors |
| Water droplet size | Very small (typically <0.1 mm) | Larger (0.5–2 mm) |
| Appearance | Diffuse, ethereal arch | Sharp, bright arc |
| Frequency | Rare | Common during rain |
Where and Why Do Fogbows Form?
In Australia, fogbows are most likely to appear in south-eastern regions during autumn and winter, when radiation fog forms overnight. The fog must be shallow and uniform, with the sun low on the horizon. Marie Johnson, a resident of Cobar in outback New South Wales, captured one such fogbow early one morning. “It was like a rainbow, but it’s white,” she said.
Key Takeaways About Fogbows
- Fogbows are rarer than rainbows and require specific conditions: fog, low sun behind you, and clear line of sight.
- They appear white due to the small size of fog droplets (less than 50 microns).
- Best viewing times are early morning in fog-prone areas of Australia, especially autumn and winter.
- You can also see a fogbow at night if the moon is bright enough—called a lunar fogbow.
Frequently Asked Questions About Fogbows
What causes a fogbow to be white?
The tiny water droplets in fog are so small that they cause diffraction, which spreads light without separating it into distinct colors. This results in a white or faintly colored arc.
Can a fogbow be seen at night?
Yes, if the moon is bright enough and positioned behind you, a lunar fogbow can appear. It will look even paler than a daytime fogbow.
Where is the best place to see a fogbow in Australia?
South-eastern Australia, particularly rural areas with open landscapes and frequent autumn/winter fog, such as the outback of New South Wales. Cobar, where Marie Johnson spotted hers, is a prime location.
Is a fogbow a type of rainbow?
A fogbow is a similar optical phenomenon to a rainbow but formed by different-sized water droplets. Both rely on refraction and reflection, but the fogbow lacks the full color spectrum.
If you’re lucky enough to witness a fogbow, consider yourself among a select few. This ghostly white arch is a reminder of the subtle beauty hidden in everyday weather. Next time you see thick fog at sunrise, turn your back to the sun and look—you might just spot this rare Australian treasure.