“It’s the same sky. Why does the color change like that?”
“Great question. Sunlight is actually playing a trick on our air.”
“But sunlight looks white to me. Not blue.”
“It looks white, but really every color is mixed together in it, like a rainbow all bundled into one. When that light hits our air, tiny gas molecules bounce it around in every direction, and blue light gets bounced around far more than the other colors.”
“Why does blue get bounced around more?”
“Blue light travels in shorter, tighter waves than the other colors, and that small wave size happens to be just right for bumping into air molecules and scattering everywhere. By the time it reaches your eyes, it feels like it’s coming from every direction, the whole sky at once.”
“So the sky isn’t really blue, it’s just blue light bouncing around everywhere?”
“Exactly that. But at night, we’re facing away from the Sun, so there’s no sunlight up there left to bounce at all.”
“So it just goes back to having nothing?”
“Pretty much, it goes back to the original pitch-black of space, and the stars finally get to show through, since there’s no more bright scattered blue light drowning them out.”
“So the stars were there all day too? We just couldn’t see them?”
“Every single one. Blue was just too loud for the stars to be seen.”
“Mom, but sometimes the sky turns red in the evening. Why does that happen?”
“Oh, good question! Same principle again. Around sunset, sunlight has to travel through a much thicker slice of air to reach us than it does at noon, because the Sun is sitting low and the light comes in at a steep angle.”
“It passes through more air?”
“Right. During that long trip, almost all the blue light gets scattered away and lost, and only the red and orange light, which doesn’t scatter as easily, survives the whole way to your eyes.”
“That’s why sunsets are red!”
“Exactly. The sky looks like it’s changing outfits every day, but really it’s just the thickness of air the sunlight has to cross that keeps changing.”
Did You Know?
On Mars, it’s the exact opposite. The daytime sky looks reddish, and sunsets there turn blue. Reddish dust drifting in Mars’ air scatters light differently than Earth’s air does. Same physics, wildly different sky.
“So the stars are with us all day long, waiting quietly until the sky calms down enough for their voices to be heard.”
Your Turn Now
Share with someone today what you remember.
- Why does blue light scatter more than other colors?
- Do the stars really disappear during the day?
- Why does the sky go dark at night?
- Why do sunsets turn red?
(Check when ready: 1. Its short waves bump into air molecules easily and scatter. 2. No, they’re still there, just hidden behind scattered blue light. 3. We’re facing away from the Sun, so there’s no light left to scatter. 4. Light crosses more air and loses its blue along the way, leaving only red.)
Tonight, look up at the sky and picture the stars quietly hiding behind all that blue.
답글 남기기