Why is the sky blue?

The sky

The sky in language is what corresponds to the earth or higher space surrounding the earth, and the sky from everything: above, as for the sky in the language of science, it is part of the Earth's atmosphere, or outer space that the viewer can see from the surface of planet Earth, or the surface of any other space object It can also be defined as the most dense gaseous region of the planet. The sky appears in several colors in a single day, so during the day it is a bright blue, while at night it appears as a black surface in which the bright stars shine.

The color of the sky

When we look at the sky on a clear day, we see its beautiful blue color, and we wonder why the sky appears blue, and is the sky really blue. To find out why the sky appears blue, we must know how to see the colors first. White light consists of different wavelengths in the seven colors of the spectrum: red, which has the longest wavelength; Whereas, its wavelength is (665) nanometers, and violet has the shortest wavelength. As its wavelength is (400) nanometers, and among them various colors are presented as orange (630 nm), yellow (600 nm), green (550 nm), blue (470 nm), and indigo (452 ​​nm).

Sunlight - an example of white light - is described as multi-colored. Because it consists of the seven colors that we mentioned earlier, and when sunlight falls on objects, it absorbs some colors (wavelengths) and reflects other colors, and the colors that we see are the wavelengths that are reflected, for example we see a blue shirt because the dye particles in the cloth absorbed all The wavelengths (colors) of light reflected to our eyes the blue color only, and we see a red book because it absorbed all the colors and reflected to our eyes only the red color, as for white bodies we see them as well because they reflect all the colors and absorb nothing, and black bodies absorb all colors and do not reflect anything we see black.

When the sunlight reaches the Earth's atmosphere, it collides with the atmospheric components of the gases and particles of the air, and part of it is scattered and the other part is absorbed, and this is known as Rayleigh scattering. That is, the flexible or selective scattering of light as a result of the influence of fine particles in the atmosphere of no more than one-tenth of the wavelength of light. The scattering of light depends on its wavelength, so we find that the ratio of the scattering of the blue light, the violet light exceeds the scattering of the red light, and the yellow light because they have shorter wavelengths, and in fact the violet light is scattered 9.4 times more than the red light, so why do we see the sky Blue light, not purple, even though violet light (its wavelength is 400 nanometers) has a wavelength shorter than blue light (its wavelength is 450 nanometers)?

This is because the human eye is more sensitive to blue light than violet light, and because some violet light is absorbed in the upper atmosphere.

Sometimes the sky appears gray; This is due to the presence of drops of water in the form of clouds, or moisture in the atmosphere, so the water droplets act in contrast to all colors of the spectrum; This means that we see a faint white light, like white light when it passes through a white paper. [6] As for the sunrise and sunset, the color of the sky tends to be red, and this is because the sun in the period of sunrise and sunset is outwardly farther from the earth, so the red light The large wavelength is the light that scatters first and is able to penetrate the lower layers of the atmosphere, and it is worth noting that all of the dust, smoke and pollution contribute to additional scattering of red light, so; The sky is redder at sunset than at sunrise. Due to the accumulation of smoke and dust during the late hours of the day compared to the late hours of the night and dawn; That is, just before sunrise.

Written by Sherine Ahmed

Mawdoo3