Colors of the Sky

Akku: Mommy, why is the sky red during sunset and sunrise?

Wow Akku, this is a very common question all the kids love to know. First let me explain why the sky is blue.

The light from the Sun looks white. But it is really made up of all the colors of the rainbow. Earth’s atmosphere is a mixture of the molecules (both gas and other types) that surround the earth. When sunlight reaches Earth’s atmosphere, light of longer wavelengths, like red, yellow, and orange, easily passes through, while light of shorter wavelengths, such as blue and violet, is absorbed and then scattered in all directions by the gas molecules. 

When you look up at the sky during the day, this scattered blue and violet light reaches your eyes, however, the human eye is more receptive to blue frequencies than violet frequencies, so the sky looks blue. Scientists call this Rayleigh scattering. This is why we see a blue sky most of the time.

Akku: Wow, that’s so cool. So mommy, is the sky blue on other planets, too?

It all depends on what’s in the atmosphere. For example, Mars has a very thin atmosphere made up of carbon dioxide and filled with fine dust particles. These fine particles scatter light differently than the gases and particles in Earth’s atmosphere. Photos from NASA’s rovers and landers on Mars have shown that at sunset there is actually the opposite of what we experience on Earth. During the daytime, the Martian sky takes on an orange or reddish color. But as the Sun sets, the sky around the Sun begins to take on a blue-grey tone.

Akku: Interesting! But mommy, then why is the sky red during sunset and sunrise?

During sunsets and sunrises, when the Sun is closer to the horizon, sunlight passes through more air than during the day, when the sun is higher in the sky. More atmosphere means more molecules to scatter the violet and blue light away from your eyes.

If the path is long enough, all of the blue and violet light scatters out of our line of sight. The other colors continue on their way to our eyes. This is why sunsets are often yellow, orange, and red. And because red has the longest wavelength of any visible light, the sun is red when it’s on the horizon.

Akku: Wow nice. Thanks Mommy! This is a lot of info. See you later.

Sure Sweetie! Waiting for more curious questions!