Why Are Sunsets a Different Color?

(Last Updated On: May 5, 2021)

At some point in your life you’ve probably had the opportunity to appreciate a sunset (or sunrise!). If you haven’t in person, you’ve probably seen pictures. Well, given that the thumbnail is a picture you definitely have seen at least one now. There’s a reason sunsets are used as a shorthand for fleeting beauty. But besides looking really pretty, sunrises and sunsets are both very distinctly red (or orange it’s a spectrum). What makes them so special; why are sunsets a different color?

Why Is the Sky Even Blue? Is it because of the Ocean?

We should probably lay the foundation for the sky’s base color first. It’s a pretty common question and, no, it’s not because the ocean is blue and the sky is reflecting its color or whatever. 

It’s also not why the ocean is blue. Water is just blue. It absorbs a little more red light than everything else, which means it reflects blue sunlight back just a little more. While it’s clear in a glass, a large enough volume of water like the ocean is enough to see the effect. It’s like when you put two mirrors across from each other–eventually the reflections bouncing back and forth turn a little bit green.

Further Reading: What Color Is a Mirror?

So the sky. It’s blue thanks to Rayleigh scattering. We can treat sunlight as a wave that contains all colors to some degree. When this wave runs into the air it causes electrons and protons to vibrate at a frequency proportional to the light hitting it. Except unlike a mirror that reflects light in 30 degrees, the particles in the air just kinda reflect it all over the place. Almost like it… scatters.

Light on the blue end of the visual spectrum has more energy than light on the red side–which means particles affected by the blue parts of sunlight vibrate faster. The more they vibrate the more they scatter. While light scatters in all directions, we see what scatters and happens to line up with our eyeballs. Blue light scatters way more than red (by like a factor of 10), and thus, the sky is blue. 

You might be asking why the sky isn’t violet, since violet is even higher energy than blue. It’s just a factor of how much sunlight makes it to Earth–more of it is blue than violet. Plus our eyes are more sensitive to blue than they are violet, so we don’t see the violet hues. 

Sunrise and Sunset

When the Sun is high in the sky, we get blue. Or blue-ish violet that we see as blue. Anyway, the Sun moves through the sky over the course of the day, and when it’s closer to the horizon we get the chance to see light that has not been scattered–lower energy light. That’s because sunlight has farther to travel to get to our eyeballs when the Sun is closer to the horizon–blue light gets so scattered before it hits our eyes that we can’t really see it anymore. What’s left? 

Red.


See if you know what city you’re in by sunset here.

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About Kyler 728 Articles
Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.