Why is the sky blue?
In order, to answer this question it is necessary to understand what is the sky and everything in it. On a clear day, when there are no clouds and the sky is clear we see it to be blue. In the sky, there is air and moisture. The air is made up of several gases like oxygen and other particles like dust, pollens from flowers and other particles from many things in the earth. Pollution also adds other gasses like smoke and soot in the air.
These gasses and particles in the air are not the same everywhere. In some places, there are more than others, for example, near a factory there is more smoke and particles from the factory. In other places, the particles in the air are less than others, for instance around a forest there is more moisture and oxygen than other particles like dust or soot. Some places like mines, construction sites and active volcano have more dust in the air because of the eruptions and explosions.
The sky has a lot of moisture which makes the rain. When it rains there is a lot of moisture in the air. Also near rivers, lakes and oceans the moisture is very high because when the water becomes warm from the sun, it evaporates into the sky. All these contents of the sky contribute in one way or another in making the sky blue. Generally the sky is not blue as we see it but the gasses and particles of various kinds in the sky help in making it appear to be blue.
Since most of these particles come from the earth, they are more near the earth’s surface and fewer as a person goes higher into the sky. Therefore, as a person moves higher into the sky, it becomes less blue. The sky is blue during the daytime and black at night. This is because, during the day, there is light from the sun while; at night, there is absence of light.
It is, therefore, true that, in the presence of light, the sky is blue. It is important to know how the presence of light makes the sky to be blue. Light from the sun has colors which in most of the time cannot be seen. In order to see these colors, the light from the sun has to come in touch with the particles in the air. For instance, when it is raining, and there is light from the sun, a rainbow appears in many colors. These colors are already in the light the raindrops or water in the air helps in making them visible.
Therefore, light requires coming into contact with other particles in order for its colors to be visible. Light travels from the sun in waves like the wave which form when you throw something in the water. The waves that are closer are stronger that is they have more energy and vigor when moving away. As, the waves move further from the source they become weaker because of the long distance their energy is reduced.
Light behaves the same way. Therefore, the colors in the light have different energy levels. For instance, in looking at the rainbow the red color if furthest followed by orange, yellow, green, blue, then indigo and violet. The reason for these arrangements is that like waves, the colors with the strongest energy are seen to be closest while those with a weaker energy are seen to furthest.
Since light has to collide with the particles in the air to make its colors visible, not all colors are seen. The reason for this is that the colors with the strongest energy like violet and indigo have a shorter wave. When the light collides with the particles in the air, these colors with the strongest energy and short waves are quickly absorbed by the particles in the sky and are not seen by the human naked eye.
The colors with a weaker energy and very long wavelengths are scattered far across the sky to the extent that they are not visible. Colors like red and Orange which are seen mostly at the horizon when the sun is setting have weak energy levels and cannot be seen in the sky. The reason is the color particles are scattered far and wide and cannot be distinguished.
When the stronger colors like violet and indigo are absorbed by the air particles in the sky, the other strong color that dominates is blue. The blue color particles collide with the particles in the air and are scattered all over the sky. The blue particles are neither too strong to be immediately absorbed by the air particles nor are they too weak to be dispersed far and wide that they cannot be distinguished.
The blue color particles are dispersed across the sky. As the sunlight nears a person, the sky appears to be a rich blue color but is the light goes further away the sky appears to be light blue. This is because the blue color particles at a close distance have higher energy and they get weaker as they move further from the light. This explains why when looking at the horizon, the sky is light bluish or white to some extent.
Therefore, the reason why the sky is blue is because the colors in the light are dispersed by the particles in the air. Where some of the stronger colors are absorbed, and the weaker colors widely scattered to be seen. The blue color is the only that contains enough energy to be evenly scattered across the sky and thus the only visible color in the sky.