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J. Perelman
"Entertaining physics". Book 1.
Chapter 8. Reflection and refraction of light

WHY DO I GET THE GREEN LIGHT?

You will understand the reason of the phenomenon, if you remember, in what seem to us the subject, when we look at them through a glass prism. Do an experiment: keep the lens of the eye horizontally wide side down and think through it a piece of paper, pinned to the wall. You will notice that the sheet first, rose significantly above its true position, and secondly, is at the top of violet-blue border, bottom - yellow-red. Raising depends on the refraction of light, colored edges from dispersion glass, i.e. glass properties different to refract the rays of different colors. Violet and blue rays are refracted more area, so we can see at the top of violet-blue border; red refracted just weaker, and therefore the bottom edge of our paper sheet has a red border.

To better understand the future we need to discuss the origin of these colored edges. Prism decomposes white light from the paper, all colors of the spectrum, providing numerous color images of the paper sheet located, part Nalgas one another, in order of prelomlyalas. From the simultaneous action of these imposed. each other color images of the eye receives the sensation of white adds spectral colors), but the top and bottom edges are immiscible colors. The famous poet Goethe, who made this experience not to understand its meaning, imagined that he exposed so the false teachings of Newton's colors, and then wrote their own “Science of colors”, which is almost entirely based on false representations. The reader, presumably, will not repeat the errors of the great poet and will not expect the prism Perekrest for all items. The atmosphere of the earth is for our eyes like huge air prism facing the base down. Staring at the Sun near the horizon, we look at it through the prism gas. The disk of the Sun gets above the rim of blue and green, bottom - red-yellow. While the Sun is above the horizon, the light drive its brightness interrupts is much less bright colored stripes, and we do not notice them at all. But in the moments of sunrise and sunset, when almost all his drive is hidden below the horizon, we can see the blue border of the upper edge. It is two-tone: the above is a blue bar below the blue, from mixing blue and green rays. When the air near the horizon perfectly clear and transparent, we can see the blue border “blue ray”. But most blue rays are scattered by the atmosphere and remains one green border: the phenomenon of “green beam”. Finally, in most cases scattered cloudy atmosphere also blue and green rays are then not seen any rims: Sun rolled crimson Orb.

Pulkovo astronomer G. A. Tikhov, dedicated “green beam” special study reports some signs visibility of this phenomenon. “If the Sun is in the sunset red color and it is easy to see with the naked eye, then it is safe to say that the green beam will not.” The reason is clear: red solar disk indicates a strong scattering atmosphere blue and green light, i.e., the entire upper edges of the disk. “On the contrary, continuing the astronomer, " if the Sun did not change their usual whitish-yellow color and comes very bright (i.e., if the absorption of light by the atmosphere is small. - J. P. ), it is likely to be green beam. But here again it is important that the horizon was sharp line, without any irregularities, close to forests, buildings, etc., These conditions are best executed on the sea; that's why green beam as well known to sailors.”

So, to see the “green light”, the need to observe the Sun at the time of sunset or sunrise with a very clear sky. In the South the sky near the horizon brighter than ours, so the phenomenon of “green beam” there there more often. But here it is not as rare as many think, probably under the influence of Jules Verne novel. Persistent search “green beam” sooner or later rewarded by success. Happened to catch this beautiful phenomenon even in a telescope. Two Alsatian astronomer describe a similar observation:

“...At the last minute before sunset, when, therefore, still visible visible part of him, the disk having a wave-like moving, but sharply defined border, surrounded by a green bezel. Until the Sun came finally, this rim is not visible to the naked eye. It becomes visible only after the complete disappearance of the Sun behind the horizon. If you look in a telescope with a fairly strong increase (about 100 times), it is possible to trace in detail all phenomena: green border becomes visible at the latest 10 minutes before sunset; it limits the upper part of the disk, while on the bottom there is a red border. Border width, at first very small (only a few seconds of arc), increases as the going down of the Sun; sometimes it reaches up to half a minute of arc. Above the green bezel frequent green as protrusions that with the gradual disappearance of the Sun as if gliding along its edge to the highest point; sometimes they become detached from the rim and glow for a few seconds separately until it turns off”.

Usually the phenomenon lasts for a second or two. But in exceptional circumstances the duration considerably longer. Marked the case as a “green light” was observed more than 5 minutes! The sun was setting behind a distant mountain, and quickly observer who saw the green rim of the solar disk, as if sliding down a mountainside.


Long-term follow “green ray”; the observer saw the “green light” for a ridge within 5 minutes. Above right - the “green light”, visible in the telescope. The disk of the Sun has the wrong paths. In position 1 the brilliance of the solar disk blinds the eyes and makes it difficult to see the green border with the naked eye. In position 2, when the disk of the Sun almost disappears, the “green light” becomes available to the naked eye.

Very instructive sightings of the “green ray” at the rising of the Sun, when the upper edge of the light begins to appear from below the horizon. This refutes often expressed a guess that “green light” is an optical illusion, which lends itself to the eye, weary glitter just rolled the Sun.

The sun is not only light, sending the “green ray”. Happened to see this phenomenon is caused by the setting of Venus.

Entertaining physics J. Perelman

 




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