Please note that to look at the Sun on the horizon you must wear good dark glasses because the air mass between the observer and the Sun filters on average only 1/10,000 of its brightness, unlike commercial solar filters which absorb 10 times more, i.e. 1/100,000.
“...If there is green in Paradise, it is surely that green, the true color of Hope”. Thus the French writer Jules Verne describes the green ray in the romantic novel Le Rayon Vert of 1882.
The writer continues: “...a green ray, but a marvelous green, a green that no painter can obtain on his palette, a green of which neither nature nor the variety of plants, nor in the color of the clearest sea, has ever reproduced the shade!..”
Many believe it is a legendary phenomenon; instead it is real, and not even that hard to observe. If we had the habit of pausing a moment in contemplation, as the Sun sets or rises, in the few minutes when we can watch our star without shielding ourselves from excessive light, perhaps we would notice it without going to exotic countries where it is believed to be more visible.
The green ray is without doubt one of the atmospheric phenomena that most strikes human imagination and fantasy. It consists of seeing a faint green streak, which forms on the top of the solar disk at sunset or sunrise; in particular conditions, it can turn into a real green flash, or fade into blue/indigo and thus become the blue ray, but green is the most common hue.
Definition of green ray from the World Meteorological Organization:<<A predominantly green coloration of short duration, often in the form a flash, seen at the estreme upper edge of the Sun, Moon or sometimes even planet when disappearing below or appearing above the horizon>>.
The main physical conditions under which the phenomenon occurs are atmospheric refraction, dispersion and selective absorption. It is a particular case within the mirage family.
It can appear in two different ways: in the first case, when the solar disk is very flattened and clearly visible above the horizon, a very thin green arc can form for many seconds, detaching from the upper limb of the Sun and fraying into one or more green filaments (green rim). This case is called M-Mir (Mock Mirage) and can last a few tens of seconds. In the second case, the most famous one, the Sun is almost completely below the horizon line and one can observe the almost instantaneous formation of the green rim. Afterwards the green streaks merge, creating a single green ray (green flash). During its extinction one may also perceive a faint green flash coming from below the horizon (right where the Sun set). The latter is the green ray of literature and its duration can vary from a fraction of a second up to about 2 seconds; this depends mainly on the latitude of the observing site and on the speed of sunset during the year.
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