Why is the sky blue?

The sky is blue only in the daytime. There are several reasons why the sky is blue. The earth covered with a layer of air called the atmosphere. Although not visible, the air is actually composed of tiny particles.

The light from the sun is scattered by small particles in the atmosphere. But we know, the light from the sun consists of an alloy of all colors, from red, yellow, green, blue, to purple. The colors that have different frequencies. Red has a smaller frequency of yellow, yellow, smaller than the green, green is smaller than the blue, blue is smaller than purple. The greater the frequency of light, the stronger the light is scattered.

The color of the sky is partially scattered sunlight. Because the most widely scattered is the high-frequency color (green, blue, and purple), then the sky has a mix of those colors, which when combined into a bright blue.

Because a lot of scattered blue, then white color of the sun is not perfect, as it should have happened if all the colors combined. The color of the sun becomes a little bit orange.

In the afternoon, the sun often turns red. At that time, the sun was slanting to travel farther to reach our eyes, so that more light is scattered. That much remains is the light frequency
low, which is red.

On the moon and the planets that do not have the atmosphere, sunlight is not dissipated, so the sky is always black, although in the daytime.