Why is the sky blue?
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. The 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.
Why is sky blue in colour? Why is sea blue in colour?
The ocean looks blue because red, orange and yellow (long wavelength light) are absorbed more strongly by water than is blue (short wavelength light). So when white light from the sun enters the ocean, it is mostly the blue that gets returned. Same reason the sky is blue."In other words, the color of the ocean and the color of the sky are related but occur independently of each other: in both cases, the preferential absorption of long-wavelength (reddish) light gives rise to the blue. Note that this effect only works if the water is very pure; if the water is full of mud, algae or other impurities, the light scattered off these impurities will overwhelm the water's natural blueness.And one more thing:The sky is blue not because the atmosphere absorbs the other colors, but because the atmosphere tends to scatter shorter wavelength (blue) light to a greater extent than longer wavelength (red) light. Blue light from the sun is scattered every which way, much more so than the other colors, so when you look up at the daytime sky you see blue no matter where you look. This scattering is called 'Rayleigh scattering'; the amount of scattering goes as the frequency of the light to the 4th power. By the way, this effect is most prevalent when the particles that do the scattering are smaller than the wavelength of light, as is the case for the nitrogen and oxygen molecules in the atmosphere.
Why do we have blue skies and red sunsets?How do colloids affect such?
When we look at the sky and see that it is blue or red what we are actually seeing is the sun's light reflected (scattered) from tiny particles in the atmosphere (these can be dust particles, water molecules, CO2 and so forth). The angle that the light is being reflected depends on the light particles' (photons') energy. Highly energetic (short wave length) light will be scattered at large angles. This is the blue light. At mid day, when the sun is directly above your head and you look at other direction (towards the horizon) the light that you will see will only be the light that is deflected by a large angle - hence the blue skies. If you look towards the sun at mid day (DON'T do it without protection) you will notice that the sky has a sort of yellowish white color, because what you are seeing then is a mixture of scattered light and light directly from the sun - which contains all wavelengths. At dusk and dawn the sun is directly on the horizon and the light that you are seeing only has to be scattered at a small angle for you to see it. Red light is not energetic and scatters at low angles, therefore the red sky. If you were to look directly above you at this time you would notice that the sky is devoid of any red color and only remenents of blue remain. That is the light which is scattered at large angles, only this time the sun is on the horizon and it's light is scattered from particles directly above you. It is a well known phenomena that very polluted cities (like L.A. if you live in the USA) have beutifully colored sunsets. This is because light is more scattered more intensily by the abundance of small particles in the air. If we had a clean, atmosphere-less planet (such as mars) our skies would have been completly black and the only source of light would have been the sky and light reflected from the ground.
Why is the sky blue while the outer space is dark?
There are two things to think about here.1. Let's take the easy one first and ask "why is the daytime sky blue here on Earth?" That is a question we can answer. The daytime sky is blue because light from the nearby Sun hits molecules in the Earth's atmosphere and scatters off in all directions. The blue color of the sky is a result of this scattering process. At night, when that part of Earth is facing away from the Sun, space looks black because there is no nearby bright source of light, like the Sun, to be scattered. If you were on the Moon, which has no atmosphere, the sky would be black both night and day. You can see this in photographs taken during the Apollo Moon landings.So, now on to the harder part - if the universe is full of stars, why doesn't the light from all of them add up to make the whole sky bright all the time? It turns out that if the universe was infinitely large and infinitely old, then we would expect the night sky to be bright from the light of all those stars. Every direction you looked in space you would be looking at a star. Yet we know from experience that space is black!This paradox is known as Olbers' Paradox.It is a paradox because of the apparent contradiction between our expectation that the night sky be bright and our experience that it is black.Many different explanations have been put forward to resolve Olbers' Paradox. The best solution at present is that the universe is not infinitely old; it is somewhere around 15 billion years old. That means we can only see objects as far away as the distance light can travel in 15 billion years. The light from stars farther away than that has not yet had time to reach us and so can't contribute to making the sky bright.2.Another reason that the sky may not be bright with the visible light of all the stars is because when a source of light is moving away from you, the wavelength of that light is made longer (which for light means more red.)This means that the light from stars that are moving away from us will become shifted towards red, and may shift so far that it is no longer visible at all.(Note: You hear the same effect when an ambulance passes you, and the pitch of the siren gets lower as the ambulance travels away from you; this effect is called the Doppler Effect).
Why is the sky blue?? be creative?
Because it isn't green.