Fogbow Optical Illusion: Rarer Than a Rainbow and How It Forms 2026

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. When Marie Johnson spotted one in Cobar, New South Wales, she described it as a white rainbow. Unlike a rainbow, a fogbow forms when sunlight interacts with tiny water droplets in fog, creating a pale, ethereal arc. This phenomenon requires precise alignment of the sun, fog, and viewer, making it a true rarity in nature.

What Is a Fogbow and How Does It Differ From a Rainbow?

A fogbow, also called a mistbow, is a meteorological phenomenon where light is refracted and reflected by small water droplets in fog. While rainbows are caused by larger raindrops that separate light into vivid colors, fogbow droplets are so tiny (less than 0.05 mm) that they scatter light without producing distinct hues. The result is a ghostly white or pale blue arc. According to Ilana Cherny, senior meteorologist at the Bureau of Meteorology, the fog must be in a Goldilocks zone—dense enough for refraction but not too thick to block the light.

Where and Why Do Fogbows Form?

Fogbows are most common in regions with frequent fog, such as southeastern Australia during autumn and winter. They typically appear in the early morning when radiation fog forms overnight. The sun must be low on the horizon and directly behind the observer, with fog ahead. This alignment creates the perfect conditions for the optical illusion to emerge. Fogbows are rarer than rainbows because they demand a specific combination of fog density, sunlight angle, and viewing position.

Key Factors for Fogbow Formation

• Fog density: Must be thick enough for light interaction but not opaque.
• Sun position: Low and behind the observer, typically at sunrise or sunset.
• Water droplet size: Smaller than 0.05 mm to avoid color separation.
• Location: Areas with frequent radiation fog, like valleys or coastal regions.

Fogbow vs. Rainbow: A Comparison

Why Is a Fogbow So Rare in Australia?

In Australia, fogbows are especially uncommon because fog requires specific conditions: cool overnight temperatures, high humidity, and calm winds. Southeastern Australia, particularly in autumn and winter, provides these conditions. However, even then, the alignment of sun and fog is fleeting. Cherny notes that “the fog also needs to be right in the Goldilocks spot,” making sightings a memorable event for those lucky enough to witness one.

How to Spot a Fogbow

To increase your chances of seeing a fogbow, wake up early on foggy mornings in fog-prone areas. Face away from the rising sun and look into the fog. You may see a faint white arch or a glowing patch of light. Bring a camera—fogbows are often captured in photos as a mysterious white curve. Remember, patience is key, as the conditions change rapidly.

FAQ

Understanding the fogbow adds a layer of wonder to foggy mornings. Whether you’re in Australia or elsewhere, keep an eye out for this rare optical illusion—it’s a reminder of nature’s subtle beauty.