Reflection Rainbow in Still Water: The Secret Explained
🕐 7 min read | 🌍 Natural Wonders
🔒 Key Takeaways
- A reflection rainbow is formed when sunlight first bounces off a still water surface and THEN passes through raindrops — reversing the light path compared to a primary rainbow.
- The reflection rainbow appears higher in the sky than the original rainbow, often reaching above 42 degrees — the theoretical ceiling for a standard primary rainbow arc.
- The two bows — primary and reflection — share the same center point on the horizon, creating a dramatic X-shaped or crossing arc pattern in rare conditions.
- Still water bodies as small as 10 metres wide can produce a bright enough mirror surface to generate a visible reflection rainbow on a clear, rainy day.
You have seen a rainbow arch across the sky after rain — but have you ever seen one that seems to rise impossibly high, crossing its twin in a jaw-dropping X of color? That breathtaking spectacle is the reflection rainbow in still water, a phenomenon so rare that most meteorologists go their entire careers without witnessing it firsthand. The secret lies not in the sky above you, but in the mirror-calm surface of a lake or puddle right beneath your feet.
What Is a Reflection Rainbow in Still Water?
A reflection rainbow is a rare atmospheric optical phenomenon that forms when sunlight reflects off a perfectly still water surface before entering raindrops in the air. Unlike a standard primary rainbow — where sunlight enters raindrops directly from the sun — the reflection rainbow uses a mirrored copy of the sun, called a 'sun glint,' as its light source. This subtle difference in light origin changes everything about the resulting arc's position, shape, and altitude in the sky. The phenomenon was first systematically described by French physicist René Descartes in the 17th century, though documented sightings in literature go back centuries earlier. It is classified separately from the more familiar 'reflected rainbow,' which is simply a primary rainbow mirrored in still water below it — an important distinction even seasoned sky-watchers often confuse. The reflection rainbow is an entirely independent arc formed by an entirely different geometric light path, making it one of the most intellectually fascinating phenomena in atmospheric optics. Scientists estimate that ideal conditions for a vivid reflection rainbow occur fewer than a dozen times per year at any given location worldwide.
How Still Water Creates a Second Sun
The entire magic of a reflection rainbow begins with one deceptively simple requirement: a body of water so perfectly calm that its surface behaves like a polished silver mirror. When wind speed drops below approximately 2 metres per second, surface ripples vanish and the water achieves a specular reflectivity that can redirect up to 98% of incoming sunlight in a single coherent beam — rivalling the reflective efficiency of a laboratory mirror. This mirror effect creates what optical scientists call a 'virtual sun' or 'reflected sun image,' sitting at an equal angular distance below the horizon as the real sun sits above it. If the real sun is 20 degrees above the horizon, the virtual sun appears to shine from 20 degrees below it, essentially punching light upward into the rain curtain from an entirely different angle. Lakes, flooded rice paddies, salt flats flooded after rain, and even large, sheltered estuaries have all been documented producing this effect. The Tibetan Plateau's high-altitude lakes, with their exceptionally still, cold mornings and frequent afternoon rain, are considered among the world's best natural theaters for this phenomenon. It is no coincidence that many of the most stunning reflection rainbow photographs come from Iceland, Patagonia, and the Himalayan foothills — regions where calm lakes sit alongside dramatic storm edges.
🤔 Did You Know?
A reflection rainbow can appear ABOVE the primary rainbow — something physically impossible for any other type of standard rainbow — making it one of the rarest sights in atmospheric optics.
The Physics: Why the Reflection Rainbow Arc Climbs Higher
Here is where the science becomes truly astonishing: because the virtual sun shines from below the horizon rather than above it, the geometry of light refraction through raindrops is fundamentally altered, and the resulting rainbow arc curves upward far more steeply than its primary counterpart. A standard primary rainbow always arcs with its top at exactly 42 degrees above the antisolar point — the point in the sky directly opposite the sun. But the reflection rainbow, using a light source positioned symmetrically below the horizon, produces an arc whose center is at the antisolar point's mirror image underground, causing the visible bow to extend significantly higher into the sky — sometimes reaching 50 to 55 degrees above the horizon. The two bows — primary and reflection — share the same antisolar axis but curve in opposite directions, which means that under perfect conditions they intersect and cross each other dramatically, creating a visually stunning X-shaped or scissors-like double bow. This crossing geometry is mathematically described by Descartes' rainbow angle formula applied to two conjugate light sources separated by twice the solar elevation angle. Importantly, the color sequence of the reflection rainbow is identical to the primary rainbow — red on the outside, violet on the inside — because the refraction physics within each individual raindrop remains unchanged. The difference is purely geometric, arising from the changed angle of incoming light rather than any change in how water bends different wavelengths.
Primary Rainbow vs Reflection Rainbow: Key Differences
Understanding what separates a primary rainbow from its rarer reflection cousin helps you spot one in the wild with confidence. The primary rainbow forms when sunlight enters a raindrop's front face, reflects once off the back inner surface, and exits — producing that familiar 42-degree arc with red outermost and violet innermost. The reflection rainbow follows the identical internal raindrop path but its source light arrives from below the horizon, reflected off still water, dramatically shifting where the resulting arc appears in the sky. Visually, the reflection rainbow tends to be slightly less vibrant than the primary rainbow because the water mirror, however calm, still absorbs a small fraction of light — typically reducing intensity by 5 to 15% compared to direct sunlight. The two bows will always intersect exactly at the horizon level if the geometry is perfect, and observers standing close to the water's edge are the ones best positioned to see this convergence point. It is also worth noting that a reflection rainbow can exist without a visible primary rainbow being present — this happens when the direct sun is obscured by cloud while the water surface still receives enough direct sunlight to generate the virtual sun glint. Atmospheric optics researchers at the Meteorological Institute of Munich have catalogued over 200 confirmed photographic sightings of reflection rainbows since 1990, noting that fewer than 30% occurred simultaneously with a bright primary rainbow.
Where and When to See a Reflection Rainbow
Timing and location are everything when hunting for a reflection rainbow, and understanding the conditions stacks the odds dramatically in your favor. You need three simultaneous ingredients: low-angle sunlight (ideally when the sun is between 5 and 25 degrees above the horizon, meaning the hour after sunrise or before sunset), active rainfall in the sky directly opposite the sun, and a large, wind-sheltered body of still water behind you. The critical window is remarkably narrow — even a gentle 3 metre-per-second breeze can destroy the mirror surface entirely within minutes, erasing your virtual sun and collapsing the reflection rainbow before it reaches full brightness. Early mornings after overnight rain are statistically the most productive times, as surface winds are typically at their daily minimum and leftover rain cells can still populate the eastern sky as the sun rises in the west. Geographically, the phenomenon is not restricted to any latitude — it has been photographed in Norway, New Zealand, the Pantanal wetlands of Brazil, and the Lonar Lake crater in Maharashtra, India. The Lonar Lake sighting, documented by Indian photographer Prasad Pawar in 2018, remains one of the most widely shared reflection rainbow images in South Asian scientific media. Keep a weather app that shows rain radar, and scout your local lakes for wind-sheltered, south-facing shores — these are your best natural stages.
Photographing a Reflection Rainbow: Pro Tips
Capturing a reflection rainbow on camera requires both preparation and rapid reaction, because the phenomenon can fully form and dissolve within 10 to 15 minutes. Use a wide-angle lens — ideally 16 to 24mm on a full-frame sensor — as the full arc of a reflection rainbow combined with its primary companion can span more than 100 degrees of sky, far exceeding a standard 50mm field of view. Position yourself as close to the water's edge as safely possible, keeping the still water surface in your foreground, because the lower you are, the more dramatic the perspective of the crossing bows against the sky. Expose for the midtones of the sky rather than the rainbow itself — rainbows are inherently bright against a dark rain-cloud background, and overexposing will bleach out the delicate violet and blue inner bands. A polarizing filter, which dramatically enhances primary rainbows by cutting scattered sky glare, actually reduces a reflection rainbow's intensity because it blocks the polarized light reflected from the water surface — so leave the polarizer off for this particular shot. Shoot in RAW format to preserve the full dynamic range of the scene, as the contrast between dark storm clouds and the bright arc can span 8 to 10 stops of light. Finally, bring a tripod — the low-light conditions of early morning combined with the wide aperture needed to capture sky detail will push your shutter speed into territory where hand-holding introduces motion blur.
Final Thoughts
The reflection rainbow in still water is nature's ultimate reminder that the sky's greatest secrets are sometimes born not above you, but in the silent mirror at your feet. Next time a storm passes and the wind falls still beside a lake, turn your back to the setting sun and watch the sky — you may be moments away from witnessing one of Earth's rarest optical masterpieces. Tell us in the comments: have you ever spotted a reflection rainbow, and did you know what you were looking at?
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Frequently Asked Questions
what is the difference between a reflection rainbow and a reflected rainbow
A reflection rainbow forms when sunlight bounces off still water BEFORE hitting raindrops, creating a new, higher arc in the sky. A reflected rainbow is simply the mirror image of a primary rainbow seen in calm water below it — two entirely different phenomena that are frequently confused even in science writing.
why does a reflection rainbow appear higher than a normal rainbow
Because its light source — the sun's mirror image in still water — sits below the horizon rather than above it, the geometry of refraction pushes the arc upward beyond the 42-degree limit of a standard rainbow, sometimes reaching 50 to 55 degrees above the horizon. This is what makes the reflection rainbow visually shocking to first-time observers.
how rare is a reflection rainbow
Extremely rare — it requires simultaneous conditions of low-angle sunlight, active rainfall on the opposite horizon, and a wind-speed below about 2 metres per second over a sizeable water body. Scientists estimate ideal conditions occur fewer than a dozen times per year at any given location, making a clear sighting a genuinely exceptional event.
📚 Further Reading & Research Sources
The following journals and institutions publish peer-reviewed research on the topics covered in this article:
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Prasad Pawar / Atmospheric Optics Archive (representative image — reflection rainbow over Lonar Lake, Maharashtra, India)
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