2024-07-24 04:00:13
A rare sight can sometimes be seen when the Sun sets: the “green ray.” This brief burst of light has intrigued observers for centuries.
Image Wikimedia
The green ray is an optical phenomenon similar to the rainbow, produced by the refraction of the light of the Sun. Normally, light from the Sun is white, because it contains all the wavelengths of the visible light. However, when it passes through a denser medium, such asEarth’s atmospherethe light separates into different colors.
This separation, called refraction, is particularly visible when the Sun is near the horizon. At this time, the light traverse the thickest part of theatmosphere at an acute angle. This is why the green ray often appears just before the Sun disappears or just after it rises.
To maximize your chances of observing this phenomenon, several conditions must be met. You must be able to see the Sun close to the horizon, for example from the coast or at high altitude. In coastal regions, the green ray is more visible on warm days, when warm air rests on colder water. These layers of air promote the refraction of light.
The presence of particles in the atmosphere also plays a crucial role. They can scatter blue and violet light, making green light more visible. Johannes Courtial, an optics researcher, demonstrated this by adding milk powder to a tank of water and shining white light on it. With the right concentration of particles, green appears.
Rays of light from the Sun pass through the atmosphere, which acts like a prism.
Credit: Reproduced from “Johannes Courtial; A simple experiment that demonstrates the green flash”.
The green beam usually lasts less than a second. But, if you are lucky, this phenomenon could last for a minute or two. This rarely happens, but the green beam can continue if atmospheric conditions remain stable.
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