This is one of the first questions that children often inquire of their parents. What makes the sky blue? Why is it not red, pink, or green? The answer to this question can be found by looking at the particulates floating in the air. The Earth’s atmosphere is filled with trillions of tiny dust particles. Most of these particles, or particulates, are too small to be seen with the human eye. The smallest particulates are by coincidence the same length as the wavelength of blue light.

As the light from our Sun shines into the atmosphere, most of the colors are able to reach the Earth’s surface uninterrupted. However, because blue light has a wavelength that is the same size as the particulates in the air, this light is scattered in every direction. This blue light bounces from particulate to particulate until it eventually reaches your eyes. For this reason, no matter what direction you look in the sky, it appears to be blue. This blue light originated with the Sun, was bounced around in the sky many times, and then eventually reached your eyes.