Rainbow are an optical effect which is the result of light refraction of water droplets in the air. The perceived color of the water droplets is determined by the angle between you and the sun drops of water. Therefore, the arc seems to float in the sky and move as you walk. The sky serves as a projection screen for the optical illusion.
The main thing is to be aware of the arcs is that they are not subject or area of ”out there”, and therefore the rainbow is not enough room (so you can never get to the end, when you leave them). They are not actually arch, but in fact circular.
When the air is foggy, each water droplet acts like a mini-prism, refracting the light from a point source (the sun) and sending colored light (not mixed with one frequency of light) in many ways. Optical rainbow effect is the result of millions of drops of water of a certain color from a certain point of view.
Rainbow forms a complete circle, if it were not for the land in a way that chops rounds in the semi-finals of the arc. When the rainbow can be seen from the window of an airplane, they look like a complete circle.
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