Why do rainbows have seven colors?

Because raindrops reflect sunlight, visible light has seven colors, and the radiation in the 0.38 ~ 0.76 micron spectrum of solar radiation consists of seven colors of light: purple, blue, cyan, green, yellow, orange and red, so the rainbow has seven colors.

When sunlight shines on an object, light with a certain wavelength is absorbed by the object, and the color (reflected light) displayed by the object is the complementary color of the light of that color. If the sun shines on an object, if the object absorbs purple light with a wavelength of 400 ~435nm, the object appears yellow-green.

Visible light radiation reaching the ground varies with atmospheric turbidity, solar height, cloud cover and weather conditions.

Extended data

The causes of rainbow formation

Rainbow is formed by the scattering and reflection of sunlight on spherical water droplets in the air. When sunlight enters the water drop, it will be incident at different angles at the same time and reflected at different angles in the water drop.

The reflection of 40 to 42 degrees is the strongest, which produces the rainbow we see. When this kind of reflection is caused, the sunlight enters the water drop, refracts once, then reflects on the back of the water drop, refracts again when leaving the water drop, and always refracts twice after one reflection. Because light is reflected in water droplets, the spectrum seen by the observer is reversed, with red light at the top and other colors at the bottom.

Baidu encyclopedia-visible light

Baidu encyclopedia-rainbow