Why is the sky blue?

Simple question for you of the teeming millions.


So, what do I win? :smiley:

Reileigh scattering!!!

Don’t know if that’s spelled correctly and can’t tell you what it means. But it is an answer of sorts.

Psst, Sandy…read the link. :wink:

You guys are great! Four minutes!

Merry Christmas. :cool:

DDG is just happy 'cause someone said thank you before wandering off. Happy hols too

You might also search the Archives: Why is the sky blue?

I think the answer to this question suffers from a variation on S. J. Gould’s “Scotch Terrier Clone” syndrome. This can happen when there are a variety of mental models and methods of attacking a problem, but then a single “right answer” takes hold in the schools, spreads through all the textbooks, and becomes a “right answer” supported by immense forces of tradition, while totally pushing out all the other correct explanations.

“If you don’t have two or three different ways of explaning something, then you don’t really understand it” - R. Feynman

How about some other explanations for why the sky is blue?

You know CK, I did try to check the archives first but the search function would not let me search using the very same search terms as in the title of this thread because sky needed more than three letters. I even changed it to skies and got 0 results found.

The same thing happened to me the other day when I tried to search out information on Windows XP.

I knew the information was there in the archives. So maybe you can tell me how to properly use the search function.

Incidentally, saying the sky is blue because of Rayleigh scattering is only part of the answer. For example, violet scatters more than blue, since the wavelength is shorter. Why isn’t the sky violet? Two reasons: the Sun doesn’t put out nearly as much violet light as blue, and our eyes are more sensitive to blue light than violet.

The sky being blue is related to sunsets being red… but not water being blue. Water is blue because it absorbs red light, so only blue gets back out. White light (from the Sun) goes in, only blue gets out (unless there are coloring agents in the water like algae, silt, etc.).

Sometimes simple questions are my favorites. They lead to all sorts of fun answers, and take you on paths you might not have otherwise followed.

Here’s one…

Have you ever tried dipping out a jar of water from a muddy river? You’ll find that even though the river it totally opaque brown, the water in the jar will be almost transparent. This demonstrates the fact that “transparent” substances are often only transparent in small thicknesses, while in larger thicknesses they have very obvious color and translucence.

This is true of air, and it’s the cause of great confusion in the public. Everyone thinks that air is transparent… but then nobody understands why “the sky” is blue. In reality, air is not clear, instead it’s a misty bluish substance like very dilute fog or smoke.

Suppose we could take a large blob of air far out into space. Make our blob 50 miles in diameter. What would it look like? It would look very bright blue and opaque. On that scale, nitrogen is a blue material.

The sky is blue because air is blue.

This is called a “scale effect.” A 6ft tall human being sees a totally opaque muddy river, while an ant thinks the same river is very clear (after all, he can see through hundreds and hundreds of ant-lengths of water before the view becomes a bit obscured.)

We humans live inside a gigantic cloud of blue fog. But the fog is so dilute that we can see for miles and miles, so we have no clue that the fog even exists.

If you were stuck in a fogbank on a bright sunny day, you’d see a white wall a few feet away from you on all sides, and if you walked along, this “wall” would follow you. Above you would be the same whiteness. If someone else in the fog bank asked you “why is the sky white”, you’d say “that’s not the sky, that’s fog you’re seeing.”

If someone on a clear day asks why the sky is blue, THE ANSWER IS THE SAME. “That’s not a 'sky” you’re seeing, that’s a huge foggy opaque blue mass of air."

There is no “sky” up there. It might look like a distant blue surface, but what you’re really seeing is a foggy cloud of gas against a black background which is being lit up by the sun. I think it would greatly help our understanding if the gas was blobby like a cloud. Then we might realize that it WAS a cloud. But the atmosphere is way too smooth, and so it confuses us because we never realize that we’re gazing into the side of a slablike cloud-thing.

Now if a little kid asks you “why does the layer of atmosphere above us look blue instead of white”, THEN we can start talking about Tyndall effect, etc.

Sorry, bbeaty, I don’t buy your explanation. If the air is really blue, then wouldn’t you expect that a white piece of paper in sunlight would look blue? After all, if the red end of the spectrum had been filtered away, the white paper would certainly look blue. Clouds would look blue too. But they don’t. They’re both white.

That’s because they’re being illuminated by all colors of the spectrum - the red end of it takes the direct path, and much of the blue end of the spectrum has been scattered around, but still just as much of it finds the sheet of paper (or cloud).

Along the same lines, if it were true that “air is blue,” then looking at a white light source through lots of air, the light should look blue. But it looks more red. Light scattering is a different thing than the sky actually being blue.

Looks like you got one hook, line & sinker, bbeaty!

A similar phenomenon explains why the sea is blue. A glass of tap water looks clear but once you’ve got a few miles of it you can see cumulative effect of the blue pigment. :wink:

From England: The sky blue ??? when did this happen? :smiley:

Bare: CK meant search the Column Archives, not the Thread Archives. The Column Archives are on a different server and aren’t slow or weird.


doesn’t everyone know this already? There are better places to seek answers to this question.

Riiiight, the pigments in air and water. :wink:
Actually, that first link (kind of) explains the difference between the air and water being blue and The Bad Astronomer does it better. Air is not blue they way a shirt is blue so does it mean the same thing? I don’t think so- in fact, if you were going to give air a color, why not call it red since that’s the color if you look directly through it to the sun when there is more of it (at sunset/sunrise). It only looks blue when looked at obliquely to the sun.


Apparently not and of course not.