When we were young kids, we just loved to see rainbow; we did not know where this beautiful rainbow came from. My parents did not explain it to me, but I did learn it through high school like every body did. So I just want to refresh our memories about it.

Where can we see rainbow?

The rainbow is seen when there are water drops in the air, and the sun is behind us. Thus it is seen so often when there is a rainfall. It is also seen in the mist of water fall, fountain, and water sprinkler. We also can create rainbow, and I did it with my kids when they were young by spraying the water into the air in the sunny day.

How does the rainbow work?

Actually the rainbow is just the natural phenomena, and Isaac Newton was the 1st one to understand it after he did experiment by putting light through a prism. When the light went through the glass prism, it bent; when it came out, it bent again. He also discovered that the light coming out of the prism had different colors from red to violet. See the below picture.

That is exactly what happens to rainbow. In rainbow phenomena, the raindrops (spherical form) play the role of prism. When the sunlight enters the raindrops, the light will bend and reflect off the back of the drop; when it comes out of the rain drops, it bends again in such away that the rainbow of colors appears. See the below picture.

A rainbow can only be seen when the reflection angle between the sun, raindrops and our vision line is between 40-42 degrees. The colors of rainbow are red, orange, yellow, green, blue, indigo, and violet. The colors are called “visible spectrum”. They have wavelength between 700-400 nanometers respectively. Actually sunlight has more than just the visible spectrum. So what is the sunlight composed of?

What is light?

Before answering the question of what the sunlight is composed of, we may need to know first what light is. Usually we refer light to the light that is visible to human eyes. But there are other lights that we cannot see such as ultraviolet and infrared lights. The last two are seen by some other organisms.

Light is complicated to understand, and at this point it is defined as a stream of energy packets (photons) that travel as an electromagnetic wave. The lower wavelength (or higher frequency) it has, the higher energy it carries. Thus the higher wave length (lower frequency) it has the lower energy it carries. Light is also defined as an electromagnetic radiation with different wave length. They are categorized with Gamma wave as the highest frequency, the radio wave as the lowest frequency, and the rest are in between. See the below picture.

What is the sunlight composed of?

The sunlight is composed of Gamma, X-ray, Ultraviolet, Visible, and Infrared lights. It is called solar spectrum. When it enters the Earth, gamma and X-ray are absorbed by the Earth uppermost atmosphere, and the ultraviolet is absorbed by the ozone layer. Even though Ozone layer absorbs the ultraviolet, but there are still some penetrated to the lower atmosphere. The rest (Visible and Infrared) go through the lower atmosphere.

How about the street lights and other man-made lights?

How do we make them? Will be in another essay.