Why does a rainbow appear? Why is the sky blue during the day and black at night?

After rain, the air in the atmosphere is filled with raindrops. Each raindrop acts like a tiny prism. If sunlight passes through raindrops at right angles, the light splits into an arc of colors with red on the outside of the stripe and purple on the inside.

The brightest rainbow screens appear when part of the sky is still dark with clouds, and the viewer is in a sunny location facing the Sun. This creates a very bright rainbow against a dark background.

Sometimes a second arc or “double rainbow” can be seen. This is caused by the double reflection of sunlight inside the raindrops. Double reflection causes the colors of the second rainbow to be in reverse order of colors.