The light has barely broken when you notice it. You are standing on a clifftop or a hillside above a fog-filled valley, the new sun at your back, the world in front of you a shifting wall of white mist. Then, low against the fog, you see it: a broad, luminous arc spanning the near distance, wide and soft and holding no color you could name with certainty. It is not the sharp spectrum of a rainbow. It is ghostlier than that, wider, and in some ways more unsettling. What you are looking at is a fogbow - and if you have never seen one, you are about to discover why dedicated sunrise chasers rank it among the most compelling phenomena a morning can produce.
Fogbows form in fog and mist rather than rain, and that single change in the medium transforms the physics of the bow completely. Where a rainbow announces itself in vivid color, a fogbow arrives in near-white silence. It is broader, dimmer, and far less predictable than its better-known relative. It has been given names by sailors, described by scientists since the early eighteenth century, and largely ignored by the broader public - partly because seeing one demands being outdoors in conditions most people consider too wet, too dim, or too early. This guide covers the science behind the fogbow, the conditions that produce it, how to photograph it well, and why the experience of watching for one at dawn is worth your full attention.
What Is a Fogbow?
A fogbow is an arc of diffuse, mostly white light that appears opposite the sun in a bank of fog, mist, or low cloud. Like a rainbow, it is centered on the antisolar point - the point directly opposite the sun from your eyes, which you can locate by finding the shadow of your own head on the fog or ground in front of you. The bow's radius is roughly the same as a primary rainbow: about 40 to 42 degrees from that antisolar point. What differs is the bow's color, width, and internal structure.
Where a primary rainbow is a vivid narrow arc roughly two degrees wide, a fogbow is a pale, broad arc that can span five to ten degrees of angular width depending on fog droplet size. It appears white or very pale, with only the faintest reddish tinge on its outer edge and the faintest bluish tinge on its inner edge. Sailors on northern sea routes called it the "sea dog" and treated it as a navigational sign; it also goes by "white rainbow," "ghost bow," and "cloud bow." All of these names describe the same phenomenon: a bow made of fog rather than rain, holding its colors undivided.
Scientific interest in fogbows goes back at least to the early eighteenth century, when observers noticed that the bow appearing in maritime mist behaved differently from the rainbow in a rain shower. Early explanations using geometric optics - the same approach that describes rainbows successfully - could not account for the fogbow's broad, colorless appearance. The correct explanation required understanding diffraction, the bending and spreading of waves around very small obstacles, which dominates the optics of fog droplets in a way it does not for raindrops. That distinction lies at the heart of everything that makes a fogbow look and behave differently from a rainbow.
Visually, a fogbow is easy to overlook. It has none of the rainbow's sharp red outer edge to catch the eye. Against a dense white fog background in poor light, it can appear as a subtle brightening of the mist rather than a defined arc. Training your eye to recognize fogbows starts with knowing where to look - 40 to 42 degrees from the shadow of your head - and accepting that the bow will be wider and softer than any rainbow experience has prepared you for.
The Science Behind the White Rainbow
Why Fog Creates a Different Bow
To understand why a fogbow is white, start with why a rainbow is colored. When sunlight enters a spherical raindrop, it refracts at the front surface, reflects off the back wall of the drop, and refracts again on exiting. Because different wavelengths of light refract at slightly different angles, they exit the drop in a spread of directions: red light leaves at about 42.4 degrees from the original ray direction, violet light leaves at about 40.5 degrees. That separation of roughly 1.9 degrees is enough to produce a clean visible spectrum. This geometric ray-tracing model works well because raindrops are many thousands of times larger than the wavelength of visible light.
Fog droplets violate the assumption that makes geometric ray-tracing accurate. Typical fog droplets are between 10 and 100 micrometers (0.01 to 0.1 mm) in diameter, while typical raindrops are 0.1 to 6 mm across - roughly ten to a hundred times larger. When a water droplet's diameter approaches the same order of magnitude as the wavelength of visible light (which ranges from about 0.4 to 0.7 micrometers), wave effects become significant. For fog droplets in the 10 to 50 micrometer range, diffraction becomes the dominant optical process rather than simple refraction.
Diffraction spreads each wavelength of light over a much wider range of exit angles than refraction alone would produce. The color bands - red, orange, yellow, green, blue, violet - each spread out over five to ten degrees instead of being confined to a narrow arc. All of those spread bands overlap each other at nearly every angle within the bow, and their combination produces near-white light. The bow is still there, in the sense that more light is still directed toward the 40 to 42-degree region than elsewhere, but the internal color segregation is almost entirely lost.
Droplet Size and the Width of the Arc
The relationship between droplet size and bow appearance follows a clear pattern: smaller droplets produce wider, whiter, and dimmer fogbows. Very small droplets below about 20 micrometers produce bows so wide and diffuse that they may be difficult to distinguish from the general brightness of the fog. Slightly larger droplets in the 40 to 100 micrometer range produce better-defined bows with slightly more visible structure at the edges. The clearest fogbows - those with the most visible supernumerary bands and the faintest but most perceptible edge colors - tend to form in fogs with droplets in the 50 to 100 micrometer range, at the larger end of typical fog droplet sizes.
This means that not all fog is equal for fogbow photography. Dense, uniform fogs - particularly radiation fogs on still autumn mornings, where the droplet size distribution is relatively narrow - tend to produce better-defined bows. Thin, wispy fogs with highly variable droplet sizes produce smeared or incomplete arcs. Watching the behavior of the fog - whether it has visible internal structure, moves as a coherent layer, or breaks into ragged patches - gives you a rough proxy for droplet uniformity before you even look for the bow.
Supernumerary Bands and Edge Colors
Look carefully at the inside of a fogbow - the region between the main arc and the antisolar point - and in good conditions you may see one or more concentric pale arcs, faintly tinted in alternating pastel greens and pinks. These are supernumerary bands, produced by wave interference between light that has taken two slightly different paths through the same fog droplet. When those two paths produce light that arrives at the same point in phase, they reinforce each other (a bright band); when they arrive out of phase, they cancel each other (a dark band). The alternating bright and dark bands produce the pastel-colored supernumerary arcs inside the main bow.
Supernumerary bands are more pronounced in fogbows than in rainbows precisely because fog droplets are small and uniform enough to produce stronger interference effects. A fogbow with three or four visible supernumerary bands over a well-lit, uniform fog layer is a genuinely rare and beautiful sight. These bands also occur inside ordinary rainbows, but they are frequently washed out by the range of raindrop sizes in any given shower and by the angular size of the sun itself. In a uniform fog bank with consistent droplet size, the conditions for strong supernumerary interference are far better met.
The faint reddish outer edge and bluish inner edge of a fogbow exist because at the extreme ends of the visible spectrum - deep red and deep violet - the diffraction overlap is slightly less complete than for middle wavelengths. Some residual color segregation persists at the edges. These colors are rarely visible to the naked eye in typical fogbow conditions and may need modest saturation enhancement in post-processing to become apparent in photographs. They are worth looking for even when subtle, because they transform what appears to be a simple white arc into something with genuine internal structure.
When and Where Fogbows Appear
Radiation Fog at Sunrise
The most reliable conditions for a fogbow come with radiation fog - the kind that forms on still, clear nights when the land surface loses heat rapidly by radiating it into a cloudless sky. By the early morning hours, air near the ground has cooled below its dew point, and fog forms in low-lying areas: valleys, river corridors, wetlands, coastal hollows, and low farmland. This fog can be 20 to 100 meters deep just before sunrise.
Radiation fog breaks up after the sun rises and begins warming the ground, usually clearing within one to two hours of dawn. During that window, the sun is low in the sky (ideal for the antisolar geometry), the fog is present and relatively uniform, and fogbow conditions are at their best. The seasons most productive for radiation fog are autumn and spring, when nights are long enough to allow substantial ground cooling but temperatures are not so cold that the air is too dry to fog. Seek out elevated viewpoints - hilltops, ridges, bridges above valleys, escarpments - where you can look outward into the fog bank with the sun rising behind you. Standing at or just above the fog surface gives you the clearest view of the bow against its background.
Coastal Advection Fog
On coastlines, advection fog forms when warm, moist air moves over cooler ocean water and chills to its dew point. This fog can be far more persistent than radiation fog, lasting through most of the morning and sometimes through the entire day. It is associated with some of the most famous fog-prone coastlines in the world: the Pacific coast of California and Oregon, the Pacific Northwest, coastal British Columbia, the coasts of the British Isles, Brittany in France, the Cape Peninsula in South Africa, and the coastal regions of New Zealand's South Island.
Beaches, headlands, and sea cliffs where you can stand with the sun at your back while looking into offshore fog or into a fog-filled bay are productive locations for coastal fogbow sightings. The key requirement is a gap in the fog overhead - you need to be in clear air with the sun behind you while looking into fog in front of you, not standing inside a uniform fog bank where visibility is too low to see the arc. This gap condition is most common at the landward edge of advection fog, where it meets the clearer air of the shore.
Mountain and Valley Fog
In mountain terrain, cloud frequently drops to valley or ridge level, and photographers who position themselves at or just above the cloud surface are well placed for a fogbow sighting from above. A fogbow observed from above a fog layer - looking down at the arc curving across the cloud surface - is sometimes called a cloudbow, though the physics is identical. From sufficiently high elevation with the sun at the right angle, it is possible to see a full circular fogbow: a complete ring of pale light on the cloud below your feet. This is most likely from aircraft or high mountain ridges, but elevated trail junctions and summit plateaus can offer the geometry needed if the cloud layer is close enough.
Planning Your Fogbow Chase
Fogbow sightings are rarely accidental. The standard planning approach is to watch evening weather forecasts for a temperature-dew point spread of two degrees Celsius or less combined with calm winds, clear skies, and high relative humidity. These are the classic preconditions for radiation fog. Many weather apps include fog forecast layers; aviation METAR reports, available for airports worldwide through national meteorological services, show current visibility and fog conditions in real time. A METAR reporting "FG" with visibility below one kilometer tells you that surface fog is present. If you can position yourself above that fog layer on a nearby hill before sunrise, you are in position for a fogbow sighting.
For coastal fog, check sea surface temperature charts alongside air temperature forecasts. When warm, humid air masses are forecast to move over cold ocean currents, advection fog is likely the following morning. Always verify current fog conditions through an official weather service before making the journey - fog is notoriously difficult to forecast precisely at the local level, and arriving an hour early is always better than arriving on time to find the fog has already cleared.
How to Photograph a Fogbow
Positioning Yourself Correctly
The fundamental requirement for fogbow photography is straightforward: sun behind you, fog in front of you, an unobstructed view in the direction of the antisolar point. The antisolar point is located at the shadow of your head. The fogbow arc will be centered on that point and will appear at a radius of about 40 to 42 degrees from it. If you are standing on flat ground at sunrise, the antisolar point is near the horizon and the fogbow arc will appear mostly above the horizon, sweeping upward from both sides.
If you are on elevated ground above a fog layer, the antisolar point is below the visible horizon (below the fog surface), and the fogbow will appear as an arc curving across the fog below you. This is the classic "fogbow across the valley" image: a white arc spanning fog between you and a distant hillside. Any obstruction in the antisolar direction - a building, trees, your camera bag, your own body when it is not behind the camera - falls at the center of the bow. Clear that sight line before looking for the arc.
Exposure in Fog
Fog is a metering challenge. It is bright - a highly reflective white medium - and camera meters tend to interpret it as middle gray, which causes underexposure. The result is an image where the fog appears gray instead of white and the fogbow, already subtle, disappears into a muddy background. Apply positive exposure compensation: typically plus 0.5 to plus 1.5 stops, depending on how dominant the white fog is in your frame. After your first exposure, check the histogram and move it as far right as you can without clipping the highlights. The goal is a bright, luminous fog background against which the arc is visible as a slight brightening with structural edges.
Shoot in RAW format without exception. Fog dramatically reduces scene contrast, and a RAW file gives you full control over recovering shadow detail, pulling out the subtle tonal structure of the bow, and coaxing out the faint edge colors that are invisible in a flat JPEG. For aperture, f/8 to f/11 provides maximum sharpness across the full arc width. Keep ISO as low as your exposure allows - fogbow scenes reward clean, low-noise files, and the soft, luminous quality you are after is better preserved in a clean file than in a noisy one.
A circular polarizing filter is worth trying, though its effect on fogbows differs from its well-known effect on rainbows. Fog scatters light in many directions, partially randomizing polarization, so a polarizer cannot suppress the fogbow itself the way it can suppress a rainbow. What it can do is reduce the overall brightness and glare of the fog, slightly increasing the apparent contrast of the bow against its background. Rotate the filter slowly and assess the effect on your live view before committing to an exposure.
Lenses, Focus, and Composition
A wide-angle lens in the 16 to 24 mm range on a full-frame body captures the full fogbow arc in a horizontal frame, since the bow spans roughly 80 to 85 degrees from side to side. A standard zoom at its widest setting will capture most of the arc but may clip the ends in a horizontal composition. Portrait (vertical) orientation at a wider focal length can include the full arc plus foreground and sky in a single frame.
Autofocus hunts in fog. The lack of hard edges and the continuous shifting of the mist means that AF systems often fail to lock or lock on the wrong plane. Use manual focus set to hyperfocal distance for your focal length and aperture, or confirm focus on a distant dark object at the edge of the fog before swinging to frame the bow. For most wide-angle shots of a fogbow over a distant fog layer, setting focus to infinity is reliable.
Compose with the antisolar point - the center of the bow - over something of visual interest. A foggy field, a river valley, an estuary, a silhouetted tree line, or a coastline provides context and scale that transforms a bow-in-mist record shot into a finished image. Including a foreground element (a fence post, a rock, a standing figure) anchors the viewer and communicates the arc's true scale. The best fogbow images use the bow's geometry as a structural element within a broader landscape, rather than treating the arc as the only subject.
A telephoto zoom in the 100 to 200 mm range can be used to crop into a section of the bow to show supernumerary bands or to isolate the delicate edge colors in detail. These close-up shots complement wide-angle arc images well in a finished set from a single fogbow morning.
Post-Processing
Fogbow images look flat straight from camera, and that is entirely expected. Begin by boosting contrast and clarity to bring out the bow's structure. The whites and highlights slider in Lightroom or equivalent software may need to be lifted to restore the fog to a bright, luminous appearance after contrast enhancement darkens it. Use the HSL panel to selectively boost orange-red saturation to bring out the outer edge tints and blue-violet saturation to show the inner edge tints, leaving the other channels relatively unchanged. These are subtle adjustments - large saturation boosts will produce artifacts rather than genuine color.
For supernumerary bands, apply a local adjustment mask over the inside of the bow arc and boost texture, clarity, and local contrast. The bands are present in the data if you exposed correctly - they may simply need help becoming visible. Correct lens chromatic aberration before attempting to interpret edge colors in the bow, since color fringing from your lens can easily be mistaken for genuine bow coloration.
Mindfulness and the Fogbow
A fogbow asks something of you that most optical phenomena do not: it asks you to be present in conditions that most people consider unfavorable. Cold, damp ground. Reduced visibility. The absence of vivid color that usually signals a photographic reward is on its way. There is no dramatic announcement. A rainbow can be spotted from inside a building through a window; a fogbow requires you to be outdoors, correctly oriented, moving through the fog to find the right angle, awake before most people have considered waking.
The conditions that produce fogbows - still air, cooling land, humidity near saturation - also produce a distinctive quality of silence. Fog absorbs sound. The usual sounds of a landscape are muffled or absent. This acoustic quality, combined with the reduced visual range, creates a sensory environment quite different from an ordinary clear morning. You become aware of small things: the damp on your jacket, the texture of the light coming through mist, the sound of your own footsteps on wet grass. This is the state of heightened attentiveness that experienced nature photographers describe as one of the genuine rewards of going out early in difficult conditions.
The white light of a fogbow carries a different quality from the split spectrum of a rainbow. A rainbow separates light into its components; a fogbow holds them together, undivided. If you are drawn to threshold states and liminal light - the light between night and day, the light at the boundary of visibility - then the fogbow is precisely the phenomenon for you. It exists only at the edge where clear air meets fog, in the brief window between the sun's rising and the fog's dispersal. It cannot be predicted with certainty. It cannot be forced. It can only be attended to.
The discipline of returning to the same fog-prone location across different seasons and weather windows - learning its fog patterns, its light angles, its usual clearing times - is a form of slow, deliberate attention to a single place. Many fogbow outings produce no fogbow at all. The fog is too thick, too thin, the sun angle is wrong, or the gap in the cloud needed to let the sun through never materializes. These mornings are not wasted. The act of being in fog at dawn, present to the particular silence and diffuse luminosity that fog creates, is its own experience. The fogbow, when it comes, is a reward for the mornings that did not deliver one.
Frequently Asked Questions
What is the difference between a fogbow and a rainbow?
Both appear at around 40 to 42 degrees from the antisolar point, but they form in water droplets of very different sizes. Rainbows form in large raindrops (0.1 mm to 6 mm), where geometric refraction cleanly separates colors into a vivid spectrum. Fogbows form in tiny fog droplets (10 to 100 micrometers), where diffraction is the dominant optical process and blurs all the color bands together into near-white. A fogbow is also typically five to ten degrees wide compared to a primary rainbow's roughly two degrees, and considerably dimmer.
Why is a fogbow white instead of colored?
The color in a rainbow comes from geometric refraction, which directs different wavelengths of light to slightly different angles - red at 42.4 degrees, violet at 40.5 degrees - producing a clean spectrum. When water droplets are very small, as in fog, diffraction spreads each wavelength over a much wider range of angles. With fog droplets below about 50 to 60 micrometers across, the color bands spread so wide that they overlap almost completely, mixing back into near-white. Only the outer and inner edges of the fogbow may show faint reddish and bluish tints where the overlap is least complete.
What time of day is best for seeing a fogbow?
The best window is the first one to two hours after sunrise, when radiation fog is still present but the sun has risen enough to illuminate it from behind you at the correct angle. Most sightings occur when the sun is below about 40 degrees of elevation. Coastal advection fog can persist later into the morning and sometimes through the entire day, extending the window considerably on appropriate coastlines. Afternoon fogbows are possible but far less common than those seen at or just after dawn.
Where are the best places to see fogbows?
Any location that experiences regular morning radiation fog or coastal advection fog is a candidate. Elevated viewpoints above valley fog are particularly productive - you can look down into the fog with the rising sun behind you. Coastlines prone to sea fog such as coastal California, the Pacific Northwest, the British Isles, Brittany in France, and coastal New Zealand offer reliable advection fog conditions. River valleys, wetlands, and low-lying farmland after clear autumn or spring nights develop radiation fog predictably. Always verify current fog conditions through an official weather service before making the journey.
Can I photograph a fogbow with a smartphone?
Yes, though with some limitations. Modern smartphones can record fogbows, particularly the wide arc shape and overall white glow. The main challenge is that phone cameras use aggressive automatic processing that tends to flatten contrast and suppress the bow's subtle tonal gradient. Use manual or pro mode if available, apply positive exposure compensation, and avoid automatic HDR modes, which can distort the gentle tonal structure of the bow. If your phone supports shooting in RAW format, use it - RAW files give you far more control over contrast and color recovery than in-camera JPEGs.
Can a fogbow appear at night?
In principle, a fogbow illuminated by moonlight is possible under a bright full moon, following the same geometry as a standard fogbow. In practice these are exceedingly rare: the full moon provides roughly one four-hundred-thousandth of the sun's light, making the resulting bow far too faint for the naked eye. Long-exposure photography might reveal such a bow as a faint white arc, but reported sightings are genuinely uncommon even among dedicated atmospheric optics photographers. The conditions required - full moon, correct elevation above or in front of a fog layer, correct geometry - align rarely enough that a moon fogbow remains a genuinely unusual occurrence.
If a foggy dawn has ever caught your attention and you are thinking about making it a deliberate practice, the contact page is a good place to start. We are always interested in hearing about locations, conditions, and photographs from people chasing this particular quality of light - the community of people who wake early for a white arc in the mist is small, and the conversations are always worth having.