If you show people a cloudy, overcast day side-by-side with a bright, sunny one, almost everyone will choose the sunny day as the one that makes them happier.
Dave, one of Starts With A Bang‘s longest readers, is no exception. The extended winter he’s living through in Kansas isn’t making him any happier:
Someone remind me what the Sun looks like, it’s been a couple of days since I’ve seen it….
No problem, Dave. Sure, there are good reasons that you want to see the Sun, for the effects it has on regulating your circadian rhythms, on the release of various endorphins, for Vitamin D production, and for just plain making you feel good. But let me remind those of you who are having extended winters what this great nuclear furnace looks like from Earth. We’ve got a Sunrise on Earth, both seen from Earth:
and also as seen from space:
Notice what the atmosphere is doing here? How the sky at sunrise looks red to us, but from space, it’s only the very lowest part of the atmosphere that looks red, and the upper parts look blue? We can learn something very interesting about light works from this.
When sunlight passes through the atmosphere, it disperses the very different wavelengths of visible light, from the bluest blues at about 400 nanometers to the deepest reds at around 700 nanometers. Since light at Earth passes through an atmosphere instead of a vacuum, the different wavelengths spread out, the same way light does when you shine it through a prism:
Well, do you notice how the blue light “bends” more due to the prism? It also bends more due to the atmosphere, which means that it gets scattered away more easily. This is why, if you look out at the sky during the early morning or late evening, the sky looks red. There’s so much atmosphere to pass through that the blue light doesn’t make it through as well as the red does. So when the Sun is low on the horizon, the atmosphere scatters the blue light away, but the red light still gets to your eyes. And you see this:
But during the day, that same scattered blue light fills the upper atmosphere, but enough of the full spectrum comes straight through that the sky looks blue and the Sun looks white!
If we didn’t have the thick atmosphere we have, the sky wouldn’t look blue! (Go ask Mars if you don’t believe me.) So what about the Sun in that picture? It’s clearly white. Then, I ask, why does the Sun look yellow to you? Because of your imperfect eyes, which have the highest response in the yellow part of the spectrum. It’s also incredibly bright against a blue background, which helps fool your eyes. But it’s really white, as you can see if you look at sunlight shining down on a white piece of paper.
So I hope these images and the science of sunlight are enough to get you through the hard times, and I expect some beautiful pictures from you when the Sun does come out, my little orphan Annie!