The Sunset’s Hidden Rainbow: Proof That Green and Yellow Skies Truly Exist
I’m Kuwako Ken, your Science Trainer. Every day is an experiment.
“Why is the sky blue during the day and red in the evening?” This is a beautiful mystery of nature, often discussed in science classes.
The answer lies in a phenomenon called “light scattering.” Sunlight is actually a mixture of various colors (wavelengths) of light, just like a rainbow. When this light enters the Earth’s atmosphere (the layer of air), the short-wavelength “blue light” tends to collide with air molecules and scatter in all directions. In contrast, the long-wavelength “red light” tends to resist scattering and travels straight ahead.
During the day, the sun is directly overhead, so we are bathed in the scattered “blue light” from all parts of the sky, making it appear blue. Conversely, in the evening, the sun is setting toward the horizon, so the light must travel through a much longer distance of the atmosphere. The easily scattered blue light loses its energy along the way and doesn’t reach our eyes. Instead, only the “red light,” which has a stronger tendency to travel straight, reaches us, thus painting the sky red.
…Now for the main topic. If light is made up of the “seven colors of the rainbow,” why doesn’t the sky turn “yellow” or “green”? Where did those colors in the middle of the rainbow go?
The Mystery of the Missing “Green Sky”
“Why don’t we see a yellow or green sky?” A student once asked me this question. It’s a fantastic question!
Indeed, the sky rarely turns a solid yellow or a vibrant green. One answer is that our eyes are more sensitive to the “blue” and “red” components. As a result of the scattering light blending together, we perceive the mix as either “blue” or “red.”
But is that really the whole story? Are yellow and green truly absent from the sky?
Searching for the Miraculous Moment Just Before Sunset
“No, they must be there!” If you keep looking at the sky with that thought, you can indeed spot green and yellow skies (if you’re lucky!). When I happened to be traveling in Izu, the sky was so breathtakingly beautiful that I decided to try and capture that moment with my camera.
Let’s zoom in on the area right at the horizon… Zoom!
And zoom in even closer!
You can see the colors layered in order: Red, Orange, Yellow, Green, and Blue from the bottom up!
What do you think? In that very moment the sun sets, when the air is clear, such beautiful layers of color (a gradient) can appear. This is evidence that the “distance” light travels through the atmosphere changes moment by moment as the sun sets, causing the color of the light reaching Earth to continuously shift, just like a rainbow.
The Sky’s Palette: More Than Just the Main Colors
Usually, the main colors of the sky seem to be “blue” and “red,” but as this photo proves, we can see that “yellow” and “green” are certainly present as supporting colors. The next time you have a chance to watch the sunset, look closely at the horizon just before the sun completely dips below it. Maybe you’ll encounter a miraculous “green” sky!
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