As the sun gracefully descends towards the horizon, it undergoes a captivating transformation that has captivated sky gazers for centuries. The once blazing orb gradually dims, casting a reddish glow upon the sky. However, for a fleeting moment, just as the sun's disk dwindles to a mere sliver, a remarkable spectacle unfolds - the elusive green flash emerges in all its emerald glory, painting the heavens with a mesmerizing hue before vanishing into obscurity.
The green flash is not merely a product of folklore; it is a genuine atmospheric phenomenon that can be observed under the right conditions. While a clear atmosphere typically offers the most spectacular displays, this ethereal spectacle can still manifest in other atmospheric settings. It is important to note that the color of the flash can vary, with some occurrences leaning towards yellow and exceptionally rare instances even revealing a blue hue.
While the traditional green flash occurs at the ocean's horizon, there are other variations of this phenomenon that defy the constraints of a specific backdrop. These alternative flashes unfold against diverse landscapes, providing photographers with captivating opportunities to capture their splendor. Let us delve into these lesser-known green flashes and explore the atmospheric conditions that give rise to their vibrant colors and brilliance.
Hilltop Flashes: Unlike their oceanic counterparts, hilltop green flashes occur when the sun sets behind a distant landscape feature. The interplay between the sun's rays and the surrounding atmosphere gives birth to vivid displays of green light.
Mountain Flashes: Nestled among lofty peaks, mountain green flashes offer a breathtaking spectacle. As the sun dips below the mountaintops, it creates a stunning burst of emerald radiance against the backdrop of rugged terrain.
Cloudy Skies: Contrary to popular belief, the presence of clouds does not necessarily hinder the occurrence of green flashes. In fact, clouds can enhance the phenomenon by scattering sunlight and intensifying the color display.
Sunrise Flashes: While green flashes are often associated with sunsets, they can also grace the dawning of a new day. Vigilant observers who pinpoint the precise moment and location of the sun's emergence can be rewarded with enchanting green flashes at sunrise.
The mesmerizing green flash is a result of atmospheric refraction, a phenomenon that occurs when light bends as it passes through different layers of the atmosphere. This bending effect is more pronounced near the horizon, where the Earth's curvature amplifies the refraction. As a result, the shorter wavelengths of blue and green light are refracted to a greater extent than longer wavelengths such as red and orange.
When the sun is close to the horizon, its light traverses a larger portion of the atmosphere, intensifying the refraction. As the sun's disk diminishes, the green light becomes concentrated and separates from the other colors, creating the brilliant green flash that captivates observers.
While witnessing a green flash can be an awe-inspiring experience, it is crucial to prioritize eye safety during observation. Staring directly at the sun, even during the fleeting moments of a green flash, can cause permanent damage to your eyesight. Here are some essential precautions to follow:
By adhering to these safety measures, you can protect your eyes while indulging in the wonders of atmospheric optics.
In conclusion, the green flash is a captivating phenomenon that has mystified and enchanted sky watchers for generations. Whether it emerges above the ocean's edge or against the backdrop of mountains and clouds, the green flash never fails to dazzle with its vibrant hues. Understanding the scientific principles behind this optical spectacle allows us to appreciate its ephemeral beauty even more. So, keep your eyes peeled and your camera ready, for you never know when the enigmatic green flash will grace the horizon and gift you with a truly extraordinary moment in nature's grand theater.
Two types of green flash. That on the left captured from Belgium by Florian Schaaf is an intense flash of emerald green as the last vestiga of the sun sinks beneath the horizon. This is the type usually described and seen by the eye. To the right a detached green fragment on the setting sun, imaged in the Spanish Canary islands by Tony Cook, is the green flash more often photographed. © Florian Schaaf & Tony Cook
The sun slips slowly downwards to a clear ocean horizon. Ever reddening as it sinks, soon only a thin sliver of the once hot disk is left. Then, as that too shrinks and lessens, it shines forth for just a second in a most vivid emerald green. Then it is gone, only the dark ocean remains. That is the green flash of fable.
Flashes like that do occur. A clear atmosphere produces the best ones but it is not absolutely essential. Sometimes the flash is more yellow, very rarely it is even blue. If you are energetic, observe on a hill or dune and run up after the flash has occurred - you could see another one. There are sunrise flashes too if you are alert for the very place and moment that the sun will appear.
There are other types of flash. Some do not need an ocean horizon. The next few pages describe them and the subtle atmospheric conditions that produce their colour and brilliance. There also some clues as to which sunsets will produce them. ↓
Take care of your eyes. Never stare at the sun and never look at it through binoculars, a telescope or the optical viewfinder of an SLR camera - your eyesight could be permanently damaged. ↓
This section owes much to green flash expert Andrew T Young and his site should be consulted for a definitive account. Thanks also to all the photographers for generously giving permission to use their fine images.
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"Green Flash". Atmospheric Optics. Accessed on November 30, 2023. https://atoptics.co.uk/blog/green-flash/.
"Green Flash". Atmospheric Optics, https://atoptics.co.uk/blog/green-flash/. Accessed 30 November, 2023
Green Flash. Atmospheric Optics. Retrieved from https://atoptics.co.uk/blog/green-flash/.