The Nature of Green Flash: The Phenomenon You Did Not Know About
“Have you ever watched the sun set over the horizon of the sea? Yes, without a doubt. Have you followed it to the moment when the top edge of the disk touches the horizon line and then disappears? Probably yes. But did you notice the phenomenon that occurs at that moment when the radiant light throws its last ray, if the sky is free from clouds and completely transparent? Perhaps not. Do not miss the chance to make such an observation: it is not a red flash that hits your eye, but a green, wondrous green color, such that no artist can get on his palette and nature itself does not reproduce in various shades of vegetation or color”
Myth or Reality
This article in an English newspaper led the young heroine of Jules Verne’s novel to an enthusiastic state and prompted her to take a series of journeys for the sole purpose of seeing the green flash with her own eyes.
The young Scotswoman failed, as the novelist narrates, to observe this beautiful phenomenon of nature. But it still exists. The green flash is not a legend, although a lot of legendary is connected with it. This is a phenomenon that every nature lover can admire if he searches for it with due patience.
Physics of the Phenomenon
The refraction of sunlight in the atmosphere is accompanied by their dispersion, that is, decomposition into a spectrum. At the same time, the power of refraction depends on the wavelength of the beam: the shorter the wavelength of the beam, the stronger it will rise due to atmospheric refraction.
Atmospheric dispersion of sunlight is the most obvious at the very last moment of sunset, when a small upper segment remains above the horizon, and then only the top of the solar disk. The last flash of the setting sun, decomposing into a spectrum, forms a “fan” of colored rays. The divergence of the extreme rays of the visible spectrum, violet, and red, is 38 degrees, but with stronger refraction, it can be much more. When the sun sinks below the horizon, the last flash we should see is purple. However, the very short-wave rays (purple, blue) on a long journey in the atmosphere (when the sun is already at the horizon) are so strongly scattered that they do not reach the earth’s surface. In addition, the sensitivity of the human eye is less to the rays of this part of the spectrum. Therefore, at the last moment of sunset, the last flash of the setting sun turns out to be a bright emerald color. This phenomenon and received the name of the green ray.
Observation of the Phenomenon
To observe the green ray, three conditions are necessary:
•open horizon (in the steppe, tundra, mountains or the sea in the absence of waves),
•and the cloud-free side of the horizon where the sunset or sunrise occurs.
Observation with the naked eye is a rare occurrence. Using a telescope, binoculars, and pointing the device at the sunrise point in advance, you can see it almost any day with suitable weather. You can watch no more than a few seconds – it is dangerous! At sunset, its bright light does not allow the use of optics at all.
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