Clear Sky Sunset Colours
I wanna learn about the colours at sunset and the layers of different colours when there are no clouds in the sky.
It sounds like you've been looking at the sky at just the right moments! There's something magical about how a perfectly clear, cloudless sky separates into distinct stripes of color right around twilight.
When the sky is completely clear, those gradients—from deep orange-reds near the horizon to soft pinks, and then to a dark, cold blue-purple—aren't random. They are a literal, giant map of how sunlight behaves as it struggles to travel through our atmosphere at a low angle.
I'm running a quick search to pull together the exact physics behind this beautiful layering so we can map out our journey together.
Q: How deeply would you like to explore the science behind these sunset layers? A: A deep dive into the atmospheric mechanics, including how Earth's own shadow gets projected onto the sky!
A deep dive into the atmospheric mechanics is exactly what I hoped you would choose! Understanding how the Earth itself acts as a giant shadow-caster in its own atmosphere is one of the most mind-blowing optical phenomena you can see with your own eyes.
Before we can project the Earth's shadow, we first need to understand how the atmosphere acts like a prism, separating plain white sunlight into a spectrum of vibrant colors. To get us started, I've mapped out our scientific journey.
How Air Molecules Play Favorite with Colors
Sunlight looks white to us, but it is actually a blend of all the colors of the rainbow. Each color travels as a wave, but they don't all travel the same way. Red and orange light travel in long, lazy waves, while blue and violet light zip around in short, choppy waves.
When this light enters our atmosphere, it runs into billions of tiny gas molecules (mostly nitrogen and oxygen). Because the blue waves are so small and choppy, they crash directly into these tiny molecules and get bounced—or scattered—in every direction. This selective bouncing of shorter wavelengths is a physical process called .
During the middle of the day, when the sun is overhead, this scattered blue light is bounced all over the sky, which is why the daytime sky looks bright blue to our eyes. Meanwhile, the longer red and yellow waves pass almost entirely straight through the air without hitting much, traveling directly from the sun to the ground.
Now that we know how molecules filter out blue light, we can look at what happens when the sun begins to sink toward the horizon, forcing that light to take a much longer path to reach your eyes.