Glitter paths, also known as glitter patches, are enchanting displays of light that occur when the moon or sun reflects off the undulating surface of a liquid. These mesmerizing phenomena are created by the countless instantaneous reflections of the celestial bodies from various facets of the liquid surface. The reflections occur when the facets align in just the right position and tilt, resulting in a dazzling spectacle for observers.
When observing glitter paths, one might notice horizontal striations on their surface. However, these striations do not provide any information about the direction of the waves. In fact, these apparent horizontal lines are a result of foreshortening, which occurs when undulations are viewed at shallow angles near the horizon. This optical illusion makes all types of undulations appear to have horizontal striations, regardless of their actual wave direction.
But what makes glitter paths truly remarkable? Let's delve deeper into their characteristics:
Narrow Width: Glitter paths are incredibly narrow, often measuring only the width of the moon or sun itself. This slim width is a consequence of the gentle slopes of the waves that contribute to the path's formation.
Constant Width: Despite their narrowness, glitter paths maintain a consistent width throughout their span. This constancy is determined by the angular width of the celestial body involved, rather than the absolute height of the waves.
Brightness Variation: Within a glitter path, there is typically a brighter patch where the reflection of the moon or sun would be on still water. This variation in brightness adds an extra layer of visual interest to these radiant phenomena.
Bent Paths: While most glitter paths lie at the intersection between the horizontal plane of the water and a vertical plane passing through the celestial body and the observer's eye, some paths exhibit intriguing bends or "dog legs." These bent paths can appear tilted in images due to lens distortions, adding a touch of whimsy to the already captivating scene.
The width of a glitter path is influenced by the altitude of the moon or sun and the slopes of the waves. When the water's surface is calm, resembling a mirror, only the moon or sun's mirror reflection is visible. Gentle waves with small slopes generate narrower glitter paths, with the brightest area aligning with where the reflection would be on still water. On the other hand, as waves become steeper, the glitter path widens, creating a more expansive and ethereal display.
In coastal areas, sea and ocean glitter paths often appear wider near the shore compared to the horizon. This phenomenon arises because the waves near the shore are typically steeper and may even break, leading to a broader expanse of glittering reflections.
The occurrence of bent glitter paths, like the one observed at Lake Neuchâtel in Switzerland, is relatively rare. The bend in the path may be attributed to an asymmetric distribution of wave slopes, potentially caused by localized wind patterns interacting with the surface. The shifting winds on Lake Neuchâtel, known to blow in circles and create challenges for sailors, could contribute to this unique phenomenon.
The study of light on water reveals numerous subtleties and puzzles. Whether it's observing reflections on overcast days or basking in the brilliance of sunny skies, there is always something intriguing to discover. So, next time you encounter a glitter path, take a moment to appreciate the captivating interplay between light and liquid, and let yourself be enchanted by nature's wonders.
Acknowledgments: Special thanks to David Lynch of Color & Light in Nature for his insightful analysis of the Neuchâtel glitter path sighting. Any errors or omissions in this article are solely my responsibility.
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Lunar Glitter Path, Lake Neuch�tel, Switzerland - Imaged by John Sergneri on March 13, 2009. ©John Sergneri, shown with permission.
Glitter patches (or paths) are the myriad of individual glints - instantaneous reflections of the moon or sun - from facets of the undulating and shifting liquid surface that happen at that moment to have the right position and tilt.
Glitter paths, GPs, seem to have horizontal striations but this tells us little about the wave directions. To create a path the waves do not need to be coming towards you. Foreshortening makes undulations of all sorts appear to have horizontal striations when they are viewed close to the horizon at shallow angles.
What is notable about this GP?
(1) It is very narrow, only the width of the Moon. (2) Its width is constant. (3) There is a brighter patch where the still water Moon reflection would be. (4) It is bent!
The GP width depends on the altitude of the moon or sun and the slopes (not the absolute height) of the waves. When the slopes are zero, i.e. still water, we see only a mirror reflection of the moon. Very gentle waves with small slopes give a narrow glitter path that is brighter where the reflection would be. Here at Lake Neuchâtel the waves were very gentle. The GP broadening is consequently very small and its width is set by the greater (constant) angular width of the moon. As waves get steeper the glitter path broadens.
Sea and ocean glitter paths often look wider closer to the shore than at the horizon because the waves near the shore are steeper and even breaking.
Bent paths? A 'normal' GP lies at the intersection between the horizontal plane of the water and a vertical plane passing through the moon and your eye. Such GPs can appear tilted in images because of lens distortions.
The Neuchâtel GP has a real 'dog leg'. David Lynch.. says "In my experience this is rare, While I haven't done any calculations, I suspect it is due to some sort of asymmetric slope distribution of the waves, perhaps the result of wind blowing locally on the surface, the asymmetry being related to the direction the wind is blowing relative to the vertical plane containing the sun, observer and glitter."
John Sergneri later added support: "The winds on Lac Neuchâtel are known to blow in circles, shifting around the lake, which drives the local sailors crazy. Sailing on the lake is known to be a challenge due to the ever shifting winds. Often, a local effect happens when the wind comes down off the Jura due to temperature differences, one can see the patches of the lake disturbed while all else is calm."
Light on water has many subtleties. Look at reflections, look on overcast as well as sunny days- there are puzzles a plenty.
.. My thanks to David Lynch of Color & Light in Nature, for his analysis of the Neuchâtel sighting. Errors and omissions are mine.
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"Glitter Paths". Atmospheric Optics. Accessed on November 30, 2023. https://atoptics.co.uk/blog/glitter-paths/.
"Glitter Paths". Atmospheric Optics, https://atoptics.co.uk/blog/glitter-paths/. Accessed 30 November, 2023
Glitter Paths. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/glitter-paths/.