If you’re an inquisitive person, you’ve most likely asked yourself, “why is the sky blue?” Or if you love watching the sun set over the horizon, you might have wondered, “why does the sky turn orange-red at this time?”
It’s a no-brainer that the sky turns blue during daytime, so you might assume that the reasons for this condition are just as obvious. Turns out, it’s a bit more complicated than that. Out of all the seven colors of the rainbow, why blue? In the following post, we seek to provide a detailed answer to this question. Let’s dig in!
Why the sky appears blue
To figure out why the sky appears blue, you first need to familiarize yourself with the nature of light. More specifically, how it interacts with the gas molecules that constitute the atmosphere.
Now, to the human eye, sunlight looks white. But the reality is that it’s made up of a blend of all the rainbow colors, each of which has a different wavelength and frequency.
Sunlight is assumed to be an electromagnetic wave. This is because it causes electrons and protons (charged particles) present in air molecules to move up and down as it passes through the atmosphere.
The oscillation causes the particles to generate a wave of electromagnetic radiation. This resulting wave shares the same frequency as the incoming light. However, it’s dispersed or spread over different directions. This phenomenon of the incoming light being dispersed by air molecules is what is referred to as scattering.
The blue spectrum of light has short wavelengths and high frequencies. So as sunlight penetrates the atmosphere, the blue light causes the charged particles to move faster than in other spectrums.
The faster the movement, the greater the amount of scattered light that is produced. As a result, blue light is scattered more strongly than other colors. In fact it is estimated that blue light is spread over different directions nearly 10 times more effectively than the red light.
If you were to look at a specific point in the sky, far away from the sun, you would only get to see the light that was dispersed by the air molecules in the atmosphere. Since this scattering of light happens more frequently for the blue component of light, the sky will appear to be blue.
When we observe the sun as it sets in the evening, the opposite scenario happens. Simply put, we get to see the light that wasn’t scattered as much. Since the red component of light is scattered less frequently, this is what we observe: a reddish sky.
Does the sky appear blue on other planets?
The sky takes on different colors on other planets. Usually, this depends on the components that make up the atmosphere in those areas. For instance, the atmosphere in Mars is mainly composed of carbon dioxide and fine dust particles. The particles disperse light in a slightly different way than gas molecules.
Images captured using NASA rovers traveling on Mars show that this planet experiences the exact opposite of what happens on Earth. During daytime, the sky is a shade of orange to red, then as the sun sets, it turns a blue-gray hue.
The sky appears blue because of a concept known as the scattering of light. During daytime, the blue component of light is scattered the most. As a result, the light that reaches your eyes appears blue; hence the reason why the sky appears blue. But as the sun sets over the horizon, the light that reaches the eye is the one that is scattered the least; hence the reason why the sky looks reddish.
