Why sky appear blue during day and black during night time?
92915
The sky appears blue due to the scattering of sunlight by dust particles in the air.\n\nSunlight is comprised of light in different wavelengths and can easily be split with a prism.  The dust particles in the air are of the right size that they scatter blue light preferentially.  As a result, we see the sky blue.\n\nThe sky is black at night simply because there isn't any blue light to be scattered.\n\nIncidentally, moonlight is yellow because that is the generally reflected colour off the moon's surface.  It is reflected light strongly in the yellow waveband. The yellow light is not affected by atmospheric scattering.
137401
Blue on a clear day.\nWhite if it is cloudy.\nRed on a cloudy sunset.\nBlack at night.
530719
During daylight the sky has the appearance of an opaque blue surface, but this is the result of the air scattering sunlight. [1]There is no "blue object" above the earth in any normal sense, so it is hard to say what object the sky is. The sky is thus sometimes defined as the denser gaseous zone of a planet's atmosphere. At night the sky has the appearance of a black surface or region scattered with stars. But if we then say that the sky is the entire visible universe, it would not be the same thing we see during the day. The color of the sky is a result of diffuse sky radiation.\nDiffuse 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\nThe sky is blue partly because air scatters short-wavelength light in preference to longer wavelengths. Where the sunlight is nearly tangent to the Earth's surface, the light's path through the atmosphere is so long that much of the blue and even yellow light is scattered out, leaving the sun rays and the clouds it illuminates red, at sunrise and sunset.
160687
Sky blue\n--------\n\nYou did not check the archive of previously asked questions before you posted your question about the sky's color. This has been asked and answered more than 400 times so far here. \n\nHowever, the reason the sky appears blue (at least most of the daylight hours) is that the atmosphere is mostly oxygen and nitrogen, which are just the right size molecules to scatter the blue light, but let the other colors pass unimpeded. \n\nSo when you take the blue away from the mostly white sunlight, you get sorta yellow sunlight. \n\nAs the sun sets, the sunlight passes through more air, and more blue is scattered away, leaving the sunlight even less blue, that is, more orange. \n\nAs the sun sets even farther, even more blue is scattered away, and the sunlight appears red.\n\nGrass Green\n-------------\n\nFrom the color of chlorophyll, the chemical that plants use to capture energy from sunlight. \n\nEarth Boring\n-------------\n\nIf the earth is boring, then what is not boring to you?
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The light during the day comes from our star, the sun. The sunlight has to travel through air to get to us. The sunlight looks white, but it has many colors in it (for example, a prism or a rainbow breaks the sunlight into its colors so we can see them). \n\nSome of the blue part of the sunlight cannot go through the air without getting bounced around first by the air, and so it makes it look like the blue is coming from the air in the sky instead of the sun. That is why the sky looks blue.
844556
Yes! Of course here in the UK it is not always 'blue' below the clouds! \n\nThe reason for the sky being blue is that as light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air. \n\nHowever, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue. \n\nTo get a fuller explanation (if you can bear it!) see the link below.\n\nGood question!\n\nx
124021
A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light.  When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.
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The sky is blue partly because air scatters short-wavelength light in preference to longer wavelengths. Where the sunlight is nearly tangent to the Earth's surface, the light's path through the atmosphere is so long that much of the blue and even yellow light is scattered out, leaving the sun rays and the clouds it illuminates red, at sunrise and sunset.\n\nScattering and absorption are major causes of the attenuation of radiation by the atmosphere. Scattering varies as a function of the ratio of the particle diameter to the wavelength of the radiation. When this ratio is less than about one-tenth, Rayleigh scattering occurs in which the scattering coefficient varies inversely as the fourth power of the wavelength. At larger values of the ratio of particle diameter to wavelength, the scattering varies in a complex fashion described, for spherical particles, by the Mie theory; at a ratio of the order of 10, the laws of geometric optics begin to apply.\n\nIndividual gas molecules are too small to scatter light effectively. However, in a gas, the molecules move more or less independently of each-other, unlike in liquids and solids where the density is determined the molecule's sizes. So the densities of gases, such as pure air, are subject to statistical fluctuations. Significant fluctuations are much more common on a small scale. It is mainly these density fluctuations on a small (tens of nanometers) scale that cause the sky to be blue.
1056723
The sky is blue due to the way that light is bent, it's called Rayleigh Scattering.  Sunlight is white and white light consists of all colors but when it hits our atmosphere the light is broken up into it's component colors by the particles in the atmosphere.  The shortest wavelengths don't make it through the particles but the blue light does - hence the sky appears blue when in fact it has no color ro it (it is after all, nothing but air and water).\n\nAs others have said - grass is green because of chlorophyll - the chemical in all plants and it just happens to be green.
100945
If you want a very simple answer, here it is:\n\nThe white light from the sun is a mixture of all colours of the rainbow.\n\nA clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light.  When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.
262627
It is.  It's just very dark blue so it looks black.  I'm sure you'll agree that even a "very bright" moon is a lot darker than the sun.  I took a picture at night for fifteen seconds at 1600 ISO on a hazy night and the sky came out blue.  I think the bright points (stars) add contrast to the sky that make it look dark so the haze evened the sky out.
680880
We see the blue sky because of Rayleigh scattering.  Short wavelengths (blue light) are scattered more than long wavelengths (red light).\n\nAs the sun dips below the horizon, it doesn't get dark immediately.  We still see some light, this is twilight.  At night, even though sunlight is scattered, it doesn't scatter all the way around the globe.  Hence you eventually observe a black sky.
580957
When the light from the sun hits the earth some of the light (The higher frequency or blue light) gets trapped or rather scattered by the smaller molecules in the atmosphere.  This scattering makes the sky blue because these particles reflect this blue light.\nAt night the light we are seeing is  the light of  the sun reflected off of the moon and it is much less intense.
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reflection of light\n\nDuring daylight the sky has the appearance of a deep blue surface, but this is the result of the air scattering sunlight. [1] There is no "blue object" above the earth in any normal sense, so it is hard to say what object the sky is. The sky is thus sometimes defined as the denser gaseous zone of a planet's atmosphere. At night the sky has the appearance of a black surface or region scattered with stars. But if we then say that the sky is the entire visible universe, it would not be the same thing we see during the day.
1055537
Here is something interesting to think about: When you look at the sky at night, it is black, with the stars and the moon forming points of light on that black background. So why is it that, during the day, the sky does not remain black with the sun acting as another point of light? Why does the daytime sky turn a bright blue and the stars disappear? \n\nThe first thing to recognize is that the sun is an extremely bright source of light -- much brighter than the moon. The second thing to recognize is that the atoms of nitrogen and oxygen in the atmosphere have an effect on the sunlight that passes through them. \n\nThere is a physical phenomenon called Rayleigh scattering that causes light to scatter when it passes through particles that have a diameter one-tenth that of the wavelength (color) of the light. Sunlight is made up of all different colors of light, but because of the elements in the atmosphere the color blue is scattered much more efficiently than the other colors. \n\nSo when you look at the sky on a clear day, you can see the sun as a bright disk. The blueness you see everywhere else is all of the atoms in the atmosphere scattering blue light toward you. (Because red light, yellow light, green light and the other colors aren't scattered nearly as well, you see the sky as blue.)
721278
Yes, Saturn's sky could appear blue to someone in it looking up during the day, if it were not cloudy or hazy. It would be blue for the same reason Earth's sky is blue, scattered sunlight. The sky on Mars is not blue because the air is too thin. The red color comes from dust in the air.
87869
The sky is technically clear - this can be seen on any clear night. The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air.\n\nHowever, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.