The heavenly rainbow is beautiful and at the same time difficult physical phenomenon which can be observed after a rain or during fog if the sun shines. The set of ancient beliefs and myths at the different people is connected with a rainbow, and in Russia in old times on it forecast the weather. The narrow and high rainbow foretold good weather, and wide and low – a bad weather.
The rainbow represents the meteorological phenomenon which arises in the sky. It is the huge arch consisting of different flowers. Emergence of a rainbow is promoted by the high content of moisture in air that usually occurs after a rain or fog. The multi-colored arch appears thanks to refraction of sunlight in water drops which contain in the atmosphere in the form of steam. Drops differently refract light, it depends on length of a light wave. For example, the longest waves at red color therefore this color crowns a color range of a rainbow, it belongs to the widest arch. Then red color on a range smoothly passes into orange, further in yellow, etc. The weakest on the resilience to a deviation at refraction in water – violet color, its waves the shortest therefore to the observer sees that this color belongs to the shortest arch of a rainbow – internal. The method of decomposition of white sunlight in a color range is called "dispersion". At dispersion the index of refraction of light depends on length of a light wave. In optics the phenomenon of a rainbow is called "caustic". The caustic is a light curve of a various form, in this case – a semicircle or an arch. Multi-colored beams of which the rainbow consists go parallel to the friend to the friend, without meeting therefore it is possible to observe the color transition inherent in it, throughout a rainbow. Since childhood rhymes and sayings which help to remember colors of the rainbow are familiar to all. For example, "each hunter wishes to know a saying where the pheasant sits" each school student knows. However actually, the color range of a rainbow consists not of seven flowers, them is much bigger. Primary colors pass each other through a large number of shades and intermediate flowers. It is necessary to add that the phenomenon of a rainbow of people can observe only on the sunlight course. At the same time it is impossible to see a rainbow and a star, the sun always remains behind. At the same time, the above there is an observer (on the eminence or in the plane), the more visible form of a rainbow approaches a circle.