The rainbow is a part of a circle with center (antisolari point) lying on the extension of the straight line connecting the light source and the eye of the observer. Moreover, the sun is always behind the observer. Unlike halo, at the same time to see the sun and a rainbow is impossible.
If the rainbow is formed by raindrops, she usually is observed at a distance of 1-2 km from the observer. In the spray of the fountain or waterfall is an optical phenomenon can be seen at closer distances.
During sunset or sunrise, the center of the circle of the rainbow is on the horizon opposite from the Sun side, so the rainbow is a semicircle. With increasing height of the Sun above the horizon, and decreases the size of the rainbow. For an observer from the earth rainbow becomes invisible when the sun rises over the horizon above 42 degrees.
Actually, a rainbow is a full circle, but when viewed from the earth's surface is only visible part of her arc. The higher one ascends, the greater part of the circle he is watching. With the high mountains or the plane you can see a full circle rainbow.
The colors of the rainbow.
The colors of the rainbow represent the colors of the spectrum, located from the outer edge to inner: red, orange, yellow, green, blue, Indigo and violet. Stripes of different colors gradually merge into each other, i.e. in addition to the basic colors listed in the rainbow there is also a variety of intermediate shades. Exactly seven colors in the rainbow have identified for the first time, Isaac Newton. Since we traditionally hold this view. By the way, Bulgarians disagree with us – they produce the rainbow only has six colors, and the Chinese five.
The appearance of the rainbow, its brightness and width of strips depend on the size and number of water droplets. Large droplets formed by intense, pronounced, narrow rainbow. With decreasing droplet size decreases and the brightness of the rainbow, her lines are diverging and pale.