In fact, the arc familiar to the human eye is only a part of a multi-colored circle. The entire natural phenomenon can be contemplated only from the side of an airplane, and even then only with a sufficient degree of observation.
The first studies of the shape of the rainbow back in the 17th century were carried out by the French philosopher and mathematician René Descartes. For this, the scientist used a glass ball filled with water, which made it possible to imagine how a sunbeam is reflected in a raindrop, refracting and thereby becoming visible.
Why does our eye see a rainbow in the form of an arc, and not, for example, a vertical colored strip? Here the law of optical refraction comes into force, in which a ray, passing through a raindrop located in a certain position in space, undergoes refraction and becomes visible to the human eye precisely in the shape of a circle. It is just a part of this circle that we are used to observing. The color of the rainbow ring is caused by the refraction of sunlight in spherical rain drops, their reflection from the surface of the drops, as well as diffraction (Latin diffractus – “broken”) and interference (Latin inter – “mutually” and ferio – “hitting”) reflected rays of different wavelengths.
Thus, the color spectrum of the rainbow fits into the formula known to any child: “Every hunter wants to know where the pheasant is sitting” (a mnemonic rule, where the first letter of each word means a color – red, orange, yellow, green, blue, blue, violet).
