The Sun Is Red Because The Sky Is Blue [Uncertain Principles]

SteelyKid missed the bus this morning– she was dressed and ready, but I was talking to Kate, and if there isn’t a person at the end of the driveway when the bus comes around the corner, they won’t stop. So I drove her over to school myself (which is faster, anyway). The GE research lab complex is behind her school, so there’s a nice view from the parking lot to the eastern horizon, where the sun was just poking over a big band of clouds.

“Hey, look at that cool sunset!” she said as we were walking from the car to the building.

“That’s not a sunset, honey, it’s a sunrise. It’s morning.”

“Oh, right. I don’t usually see the sunrise, because I’m usually on the bus on the opposite side.”

“Mm-hmm.”

“It looks pretty orange. The sun’s usually yellow.”

“Right, that’s because it’s sunrise. When the sun’s near the horizon, it looks more red.”

“Yeah, at sunset it’s red, too.”

“Do you know why that is?”

“Why?”

“Because the sky is blue.”

“What?”

“You see the blue sky above us? That looks blue because light from the sun that’s headed that way” (big westward hand gestures) “hits stuff in the air and gets bounced down toward us. And that works better for blue light than for red light.”

“So the sky looks blue.”

“Right. And when the sun is low on the horizon, its light passes through a lot of air to get to us, and hits a lot of stuff. So all the blue light that ought to be there gets bounced down, to make blue skies for people who live over that way,” (big eastward hand gestures). “That leaves red light, so the sun looks red to us because the sky looks blue to them.”

“Oh. That’s pretty cool.”

“Isn’t it?”

“How do you know that?”

“Well, it’s physics. The kind of science I do looks at how light interacts with stuff, and that lets us understand blue sky and red sun. It’s Rayleigh scattering.”

“Oh. I was wondering, because I didn’t think you, like, went up into the sky to look.”

“No, but that would be kind of cool… Anyway, here we are at the door. Have a good day, honey.”

“Thanks, Daddy.”

from ScienceBlogs http://ift.tt/157L5KO