What is on the sides of the rainbow?

The rainbow is a very beautiful natural phenomenon that we have all seen. But you can get a rainbow yourself by decomposing a ray of light into its components. Before Isaac Newton, no one knew that white light consists of different colors, each of which, passing through a glass prism, refracts in a different way. After that, it became clear what paints are, why they give the effect of color. If an object reflects all the rays falling on it, then this object will appear white. By covering white paper with a layer of paint, we "hold back" certain colors by reflecting a particular color.

And what is on the sides of the rainbow, where there is no color?

And what is on the sides of the rainbow, where there is no color? Famous astronomer William Herschel was the first to ask himself this question. Just like Newton, Herschel obtained a spectrum, and put a thermometer in its various parts. At the same time, at each color of the spectrum, the thermometer showed a temperature above room temperature. But the thermometer showed a particularly high temperature not in the spectrum itself, but already in the dark, next to the extreme red rays of the spectrum. There was no doubt - there are some invisible rays that are also refracted in the prism and carry more energy than the rest. These rays were called infrared, they refracted less than red and had a wavelength longer than them. Another name for these rays is heat, they are emitted by heated bodies before they begin to emit rays of the visible spectrum.

Following the publication of Herschel about the infrared rays discovered by him (1801), followed by a report by the physicist P. Ritter about invisible rays, but already lying on the other side of the rainbow, further violet. They were named ultraviolet. It is these rays that help us sunbathe.

The visible part of the spectrum includes electromagnetic waves from 4*10-5 cm (violet) to 8*10-5 cm (red). But electromagnetic waves range in length from kilometers (radio waves) to "hard" X-rays with a wavelength of about 10-8 cm. There are also shorter electromagnetic waves - the so-called gamma rays.

Why do we see only a tiny strip, as if sandwiched between the sides of the rainbow? After all, the range of electromagnetic oscillations is very wide, the waves in length change more than billions of times, but we see waves whose length changes only 2 times?

We can say that not all wavelengths of the rainbow are suitable for a person for practical purposes. Gamma rays and X-rays are emitted under special circumstances, there are hardly any around us. This is very good, as they cause what is called radiation sickness.

Long radio waves would be extremely inconvenient. They freely go around meter-sized obstacles, and we could not consider objects that are vital for us to see.

Well, the choice of a narrow strip of wavelengths, which we call visible light, exactly on this section of the electromagnetic wave scale was made by nature by chance? No, this is far from the case. First of all, the maximum radiation of the Sun's electromagnetic waves lies just in the middle of the visible spectrum, in its yellow-green region. But this is not the main thing!

The thing is that we live at the bottom of the air ocean. The earth is surrounded by an atmosphere. We consider it transparent or almost transparent. And it is such in reality, but only for a very narrow part of the spectrum, to the perception of which the eye has just adapted. Oxygen strongly absorbs ultraviolet rays. Water vapor traps infrared radiation. Long radio waves are bounced back into space due to reflections from the ionosphere.

Thus, in the process of natural selection, living organisms acquired an organ that is sensitive precisely to the radiation lying between the sides of the rainbow, and is most suitable for its purpose.

The fact that the maximum radiation of the Sun exactly falls in the middle of the rainbow should probably be considered an additional gift from nature.