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March 17th, 2017
To see a green flash...stay on the lookout. It only lasts for a second or two. It takes vigilance, watching closely at sunrise and sunset to eventually witness it. It can happen during any season and arguably anywhere on Earth. A green flash is said to be 'rare' and requires the right conditions and more importantly, the need for an observer.
What is a Green Flash?
A green flash, also referred to as an emerald flash, appears at the tip top of the sunrise just before it breaches the horizon or it is seen as the last hint of the sun setting on the horizon. It is most commonly reported at sunset, but is actually just as possible to view at either sunrise or sunset. Logically, it is easier to know when and where the sun is setting than to catch the time and place of the sun rising. Even more rare is a green ray which is a green flash accompanied by a shaft of light shooting upwards from the top of the sun. This truly is a unique effect to witness!
During that split second is when the momentary flash of green appears. Some have reported seeing more than one green flash less than a second apart from each other. It is also possible to see it when the sun is rising or setting over a mountain or even a cloud. However, the most common place to see a green flash is at sea when the wide open water and clear skies offer a horizon ideal for catching this rare atmospheric phenomenon. Basically, it is best seen when you have a distant and distinct cloud-free horizon.
Why are Green Flashes green?
Why does the top of the sun appear green? Think of the sunset and how the sun's orange and red colors look hazy and huge as the sun appears to sink and touch the horizon. The reds of a sunset are caused by the same effect as a green flash—both are caused by refraction of light. As the sun sets, the light is viewed through a greater and greater density of molecules and the light is therefore refracted as the atmospheric soup acts as a prism spreading the rainbow of light. As the light passes through water vapor and other particles in the atmosphere this prism effect causes the sunlight to absorb and refract different wavelengths of electromagnetic energy we call colors. This explains how the oceans horizon with its thermal difference of water and air create an ideal setting for a mirage. At the last seconds of a sunset the color green in the light spectrum is refracted enough to give off the mirage of green. The green appears separate, just above the red-orange setting sunlight. This optical mirage, as seen by the human eye, is a case of looking at the right place at the right time under the right conditions. Besides being green, this explains why seeing a green flash is associated with luck!
Other objects where these phenomena can be seen
Interestingly, if a planet such as Venus or Jupiter is observed through a telescope, viewed as it sets below the horizon, a greenish refracted light effect is seen. The setting planet appears to turn reddish orange as it sets on the horizon, just as the sun does, and at the last seconds appears greenish at its tip top. This visual effect lasts for a 20 arc second band and for about 1.4 seconds of time as measured by atmospheric optics. Due to the differences in the way a lens takes in light and how the human eye takes in light, this effect can appear differently, more clear and distinct, when captured by a camera with a telescopic lens.
It is said that once you seen a green flash you will never go wrong in matters of the heart. This originates largely from Jules Verne's 1882 novel "Le Rayon Vert" (The Green Ray). When something in nature is so rare and beautiful as a green flash, or better yet a brilliant green ray, humankind often attributes meaning and legends. Since it is most common on the high seas, tales of horizon gazing sailors passed on tales of the green flashes given off by the sun. Most humans today do not take the time to gaze at a sunset or the patience and focus to await the rising sun. There are potentially two chances each day! Good luck in the search for the mysterious green flash.