why is the sky blue?

no, really - why is the sky blue?

Air particles scatter light; their range of sizes means they scatter short wavelengths (blue) more than long ones (red), so when you’re not looking at the light source, you’re seeing only that light that is being reflected/scattered - the blue components. This is also the reason why smoke appears blue and why sunsets appear red.

I’m not trying to be snarky here. But this is a question my daughter asked me when I was preoccupied with reading something or other.

I said, “Raliegh Scattering.” Next thing I heard was her going, “Maaaaaa…what’d he say?”

Sorry, but the joke is on me.

Anyway, from Here

I’m gonna go ahaead and throw this question in here since the OP was brave enough to post the first one.

What color does the sun look like from space? (Or outside our atosphere?)

White?

Interesting question which I have never really considered. A quick google shows that the sun is a Type G star. This type has a temperature of 5000K-6000K and a colour of white to yellow.
Here , it says the sun has an effective temp of 5780K and

Only one way to find out, I guess. Better make a booking for one of those Virgin space tourism trips…

Okay, so short wavelengths get scattered more than long ones. But if that’s the case, why isn’t the sky violet? I vaguely remember from high school physics that the wavelengths of different colours go in the order ROYGBIV. Or is the sky blue because there’s still a little bit of the shorter wavelength colours being scattered, and the sum of them all happens to be somewhere in the middle (B)?

Dad’s answer: “I don’t know, go ask your mother.”

My daughter asked me this one this morning. Rather than get into Rayleigh scattering, I pointed out that Leonardo da Vinci had noted in hs noebooks that light scattered by smoke was blue, so he figured that the sky was blue because of such scattering. We know today that most of the scattering isn’t from smoke, but from the air molecules themselves.

She digested this a moment, then said “And the water in it, too!”
Thenm she asked me why grass was green, so that started a discussion of chlorophyll, and what other colrs plants could be, and the observation that red cabbage isn’t green.

That’s an excellent question. I believe I recall that there is more blue, because there isn’t that much violet in sunlight, and/or your eyes are not as sensitive to violet light. Seems like I read this in the book Bad Astronomy. Phil, you still lurking here?

CurtC prettyy much nailed it – your eye’s senstivity peaks in the green and is already tailing off by the time you get to violet. On top of which, as someone pointed out on another thread, there’s less violet light in sunlight at sea level than of other colors.

There’s a calculation of the observed color, based upon the inverse fourth power of scattering, the observed makeup of sunlight, and the tristimulus color theory in Warren J. Smith’s book Modern Optical Engineering. You work through the numbers, and it comes out bluish-white, as observed.

Question answered by Cecil and by The Bad Astronomer.

Makes you wonder who Rayleigh scattering is named for.

For that matter, the Sun appears white through the atmosphere, too, as long as it’s not going through too much of it (i.e., not near sunrise or sunset). It’s only by contrast with the rest of the blue sky that it appears yellow.

And has anyone told MilliCal lately that she’s very smart?

Well, at least according to this guy, the simple explanation is because air is blue. Seriously.
http://www.amasci.com/miscon/miscon4.html#blu

Sigh. If air were itself blue, then sunsets would be bluer than the noon sun, not redder. Criticizing the correct physics explanation with “what if you don’t understand that” is idiotic. And the alternate explanation there doesn’t explain anything at all.

So ------would the sky also be blue on Mars?

If not-----why not?

Too many songs and poems have been written about it to consider alteration at this point. Now eat your peas and go to bed. :smiley:

Here’s a good and easy way to demonstrate what has been covered above.

Get yerself a glass of water and put a couple of drops of milk in it.

This will represent the atmosphere, and the small droplets of milkfat are “dust”`

Now, shine a flashlight (incandescent bulbs work better than LEDs) through the glass. As you may have guessed, the flashlight is the sun. Viewed from any angle except straight on, the beam of light will appear bluish, since these wavelengths are scattered more than the longer ones. However, if you look through the glass directly at the flashlight, you will go blind. Just kidding. The light will appear more reddish than bluish because the shorter(blue) light has been scattered, leaving more of the longer wavelength (reddish) light.

Science. It’s the best.

Sorry, but I still don’t understand why the sunset/sunrise is red. Could someone elaborate about this?

It’s the flip side of wehy the sky is blue. If the sky is blue because short wavelength light is preferentuially filtered out, then direct sunlight has an excess of red light. When the light traverses more atmosphere than normal (as near sunrise and sunset) more blue light g4ets scattered out than when it’s overhead, and the sun appears more red.
There are cases of anomalous scattering, where the situation is reversed, and more red light gets scattered out and more [i[blue* light gets transmitted. This can happen when you have a lot of spherical particles all around 1 micronm in diameter, made of droplets of organic oils, or spherical dust particles. When that happens you can have a bluish or greenish sun. (Or moon, hence the expression “blue moon”). This rarely happens, justifying the expression “Once in a blue moon”. I have an article on this coming out in a couple of months in Optics and Photonics News (And don’t bother telling me about the “two full moons in a month/four full moons in a quarter” explanations, or what Cecil said. That’s covered in there, too.)