Did you know that blood is actually blue but when you get cut and oxygen hits the blood it turns red? Do you think that the sky is actually red but looks blue because of all the oxygen?
138047
As there is no source of light in the sky apart from the Sun, then everything we see is reflected light. ; Thus the sky can only look black if all reflective matter is removed.
393205
Air scatters different wavelengths of light different amounts.  We normally see the sky as blue because the sky scatters higher wavelengths of light more then lower wavelengths of light.  Blue is a short wavelength while red is a long wavelength.  Anyway, when the sun is rising or setting on the horizon you are looking through much more air to see the sun then say, at noon when the sun is straight over head.  There is so much air that you see the red, instead of the blue, because the blue has long since scattered off while the red is still able to travel through the atmosphere to your eyes.
92663
You must realize that this has been asked over 500 times here. Surely when you asked this question you were notified. Why didn't you look at some of those previous questions and answers? I probably have answered this 50 times myself. I have some very careful detailed answers here to that question, if you just look. \n\nIt is called Rayleigh-Tyndall scattering, caused by the small size of the nitrogen and oxygen molecules in the air that scatter the blue out of the sunlight, leaving it more yellowish than it would be otherwise. At sunset, the reddish color is absorbed by the ozone overhead, creating a deep blue. \n\nIf you want more details, look it up.
145430
I would say red.  The brighter red the colour of the blood, the more oxygen it carries. The darker its color, the less oxygen it carries.  Arterial blood is generally a brighter red because it has recently passed through the lungs. Venous blood is generally a darker red because it has passed through the capillaries where the oxygen is transferred from the blood to the tissues.\n\nSome people think that blood inside the body is blue but this myth probably started when someone drew a chart of the human blood system and colored the arteries red and the veins blue. This myth has been around a long time and seems to have a life of its own.
309462
Yes, it is akin to asking why red is red. In fact, it is a very deep and philosophical, almost religious, question. The short answer is that it is just one of the fundamental constants of the universe. The long answer is: google for the numerous discussions on this topic.
306655
It's actually a bluish-green.  Look at your veins that come to the surface of your skin.  Blood only turns red when it comes into contact with oxygen.
95342
Any solid mass in the heavens has some reflective properties the same as here on earth.\nA white sheet will reflect more sunlight than a black (or dark colored) sheet. In reflecting more sunlight/energy, it absorbs more heat.  I'm sure you've felt this in dark colored cars in the summer or have watched dark road patches expand and melt quicker than the packed white snow on the same surface in the winter.\nWell, all solid bodies have a certain "color"; \nMars is red because of all the iron oxide (rust) on the surface (it has no cloud cover) and that is the reflected light that we see. \nVenus looks bright, not because of its surface, but because of the clouds in the atmosphere (alot of them in its sky) and it reflects alot of the sunlight.\nStars twinkle.\nPlanets do not twinkle.\nOur moon is covered with a fine dust, greyish, almost white in color and that is the reflected light that we see.\nIf you look at the sky during a new moon you can faintly see the very dark grey of the moon. This is the light that is reflected off the earth, which hits the moon and is reflected back to us (very faint).\nMr Giraffe...all objects are reflective, even dark ones. That's how we see them.\nWhite is the entire spectrum of visible light being reflected. It is a combination of all colors.\nBlack is the absence of color being reflected.\nWhen you see the color red, it is the red part of the spectrum that is being reflected from the object. All the other colors are being absorbed. So what you see is that which is not absorbed by the object, but refkected by it.\nAny questions?
14559
Actually there is no chemistry. Its all about physics - scattering of light.\n\nLight as you know is made up of lots of colors (seven colors visible in the rainbow actually consists of millions of colors). The color depends on the wavelenth of light. Light from the sun is white meaning it has all colors (wavelengths) equally.  \nThere is a principle in physics called Raleigh scattering. Short wavelenths(blue/violet) are absorbed and scattered by the atmosphere and with longer wavelenghts (red) are not absorbed/scattered. As blue light is scattered by the atmosphere it looks blue. \n\nAt twilight, the sky looks red/pink. This is because, the sun's light dosn't get chance of scattering. As red light is least absorbed, that is the light that comes directly to us.
640265
Color is actually made up.  We are seeing waves of light and our brain is interpreting them into what we perceive as colors.  Also, we see the waves of light that are being reflected off of things.  So if we see something as being blue that means that the other waves of "color" have been absorbed.  Quite interesting really, and a very good question.  Keep it up, I have had few good questions recently and was about to give up for the night.
163325
The Earth's sky is blue because the air molecules (largely nitrogen\nand oxygen) are much smaller than the wavelength of light. When light\nencounters particles much smaller than its wavelength, the scattered\nintensity is inversely proportional to the 4'th power of the\nwavelength. This is called "Rayleigh scattering," and it means that\nhalf the wavelength is scattered with 2**4 = 16 times more intensity.\nThat's why the sky appears blue: the blue light is scattered some 16\ntimes more strongly than the red light. Rayleigh scattering is also\nthe reason why the setting Sun appears red: the blue light has been\nscattered away from the direct sunlight.\n\nThus, if the atmosphere of another planet is composed of a transparent\ngas or gases whose molecules are much smaller than the wavelength of\nlight, we would, in general, also expect the sky on that planet to\nhave a blue color.\n\nIf you want another color of the sky, you need bigger particles in the\nair. You need something bigger than molecules in the air---dust.\n\nDust particles can be many times larger than air molecules but still\nsmall enough to not fall out to the ground. If the dust particles are\nmuch larger than the wavelength of light, the scattered light will be\nneutral in color (i.e., white or gray)---this also happens in clouds\nhere on Earth, which consist of water droplets. If the dust particles\nare of approximately the same size as the wavelength of light, the\nsituation gets complex, and all sorts of interesting scattering\nphenomena may happen. This happens here on Earth from time to time,\nparticularly in desert areas, where the sky may appear white, brown,\nor some other color. Dust is also responsible for the pinkish sky on\nMars, as seen in the photographs returned from the Viking landers.\n\nIf the atmosphere contains lots of dust, the direct light from the Sun\nor Moon may occasionally get some quite unusual color. Sometimes,\ngreen and blue moons have been reported. These phenomena are quite\nrare though---they happen only "once in a blue moon...." :) The dust\nresponsible for these unusual color phenomena is most often volcanic\nin origin. When El Chicon erupted in 1982, this caused unusually\nstrongly colored sunsets in equatorial areas for more than one year.\nThe much bigger volcanic explosion at Krakatoa, some 110 years ago,\ncaused green and blue moons worldwide for a few years.\n\nOne possible exception to the above discussion is if the clouds on the\nplanet are composed of a strongly colored chemical. This might occur\non Jupiter, where the clouds are thought to contain sulfur, phosphorus,\nand/or various organic chemicals.\n\nIt's also worth pointing out that the light of the planet's primary is\nquite insignificant. Our eyes are highly adaptable to the dominating\nillumination and perceive it as "white," within a quite wide range of\npossible colors. During daytime, we perceive the light from the Sun\n(6000 K) as white, and at night we perceive the light from our\nincandescent lamps (2800 K, like a late, cool M star) as white. Only\nif we put these two lights side-by-side, at comparable intensities,\nwill we perceive a clear color difference.\n\nIf the Sun was a hot star (say of spectral type B), it's likely we\nstill would perceive its light as "white" and the sky's color as blue
251614
No, this is a very common myth. Blood is always red. When in an oxygen poor stage it assumes a red color that is not as intense as the red of the oxygen rich stage. The blue color comes from looking at your deoxygenated blood through layers of skin as well as the veins.
327461
The simplest way to explain it to a 9 year-old would be simply to say that the blue sky is actually sunlight - but all of the colours of light from the sun can pass through the air except blue, and that the sun scatters this blue light in all directions so that you see blue wherever you look.  This is also the reason why the sun appears yellow - in reality it is white because when you mix all colours together you get white - but when you take the blue light out and scatter it all over the sky, then all of the remaining colors add to give you bright yellow.
27910
first of all, to Paranoid Princess:\n\nwhoa, whoa WHOA.  just a minute.  the sky is not blue because there's liquid oxygen in the upper atmosphere.  that's just retarded and you shouldn't go presenting bizzare mis-truths as fact when they *aren't* fact.\n\nhere is a profile of temperatures at various altitudes:\nhttp://www.windows.ucar.edu/tour/link=/earth/images/profile_jpg_image.html\nas you can clearly see the lowest temperature is about -100C.  oxygen liquefies at -182C at normal pressures (reference: http://www.ucc.ie/ucc/depts/chem/dolchem/html/elem/elem008.html ), and even lower temperatures at the low pressures in the upper atmosphere.  PLEASE don't present some bizarre fiction as truth to someone who isn't well-informed enough to know that you're simply fabricating nonsense from thin air.  if you have simply been misled by someone else, at least try to do a marginal amount of research before answering a question on something you don't know much about.\n\nthat said, to the original asker:\n\nthe sky is blue because of a phenomenon called "rayleigh scattering", which occurs because the molecules of air (mostly N2 and O2) happen to be the right size to scatter blue light in all directions.  some of this blue light reaches your eye after being re-scattered again by a second molecule, sometimes all the way across the sky.  \n\nthis is also why the sky turns red at sunset - at low angles, the sunlight has to travel a longer distance through the atmosphere, and by the time it reaches your eye, a lot of the blue light has already been scattered away, leaving yellow orange and red.  (i have yet to hear any explanation of why the sky doesn't turn green between daytime and sunset, though.  still tryin' to figure that one out.)\n\nanyway here are some home/school experiments designed to illustrate rayleigh scattering:\nhttp://www.physics.brown.edu/physics/demopages/Demo/optics/demo/6f4010.htm\nhttp://www.chaosscience.org.uk/dem/public_html/article.php?story=20050222224622239\nhttp://teachers.web.cern.ch/teachers/archiv/HST2002/smallexp/krug/Rayleigh.htm\nhttp://bulldog2.redlands.edu/facultyfolder/deweerd/research/scattering-AJP.pdf\nhttp://www.ktca.org/newtons/9/sky.html\n\nalso, a nice page illustrating rayleigh scattering:\nhttp://hyperphysics.phy-astr.gsu.edu/hbase/atmos/blusky.html\nand a slightly more advanced version:\nhttp://world.std.com/~mmcirvin/bluesky.html
22935
The sky is blue because the nitrogen in the air scatters the blue light out of sunlight. \n\nOur sun is a yellow star, so it has slightly yellow light, but it is still pretty close to white light.\n\nSunlight on earth is slightly yellower than it is in space because some of the blue light in sunlight gets scattered out by the presence of nitrogen in the air, making the sky appear blue. So \n\n(White light) - (Some Blue light) = (Yellow light)\n\nAs the sun sets, the sunlight travels through more air, and the nitrogen scatters out more blue light and the sun appears first orange, and then finally red.\n\nAs the sun starts to set:\n\n(White light) - (More Blue light) = (Orange light)\n\nand finally as the sun has almost set:\n\n(White light) - (Lots of Blue light) = (Red light) \n\nEdit   Delete
530868
The answer to part one is "green", and the answer to the second part is "green".\n\nThat is why the sky actually appears blue at noon (blue light is more scattered) and red at sunset (red light is less scattered).
645
The sky appears blue because the gases(mainly nitrogen and oxygen) present in our atmosphere vibrate at a specific frequency.  From the light that we can see, ie.. blue, green, red, yellow...etc, the the higher frequency colors are absorbed more by the atmosphere than the lower frequency(actually they're scattered, they still make it to us but indirectly whereas the yellowish color of the sun is more direct).  So blue, green, and violet(violet having the shortest wavelength) are absorbed by the atmosphere, while red, yellow and orange are allowed through.   The color of blue that we perceive the sky varies from day to day based on the content of gases present and the frequency that they vibrate.  It works the same way as light passing through a blue balloon, except in this case the balloon is our atmosphere.
25776
The sky is blue due to a phenomenon known as diffuse sky radiation. Diffuse sky radiation is solar radiation reaching the earth's surface after having been scattered from the direct solar beam by molecules or suspensoids in the atmosphere.\n\nThe blue portions of the earth seen from space are of course water. Water exhibits a similar characteristic, where red light wavelengths are absorbed. This effect is only visible with large quanities of water though (like a pool or ocean), however. Water in small quantities (like a glass of water) appears clear.