A1: Blue light gets scattered (spread) around much more than all the other colors from the sun, causing the sky to appear blue:
Light is made up of electromagnetic waves. The distance between 2 crests in this wave is called the wavelength. White light contains all the colors of the rainbow.
The amount of light scattered for any given colour depends on the wavelength of that colour. All the colors in white light have different wavelengths. Red light has the longest wavelength.
The wavelength of blue light is about half that of red light.
This difference in wavelength causes blue light to be scattered nearly ten times more than red light. Lord Rayleigh studied this phenomena in detail. It is caused the Tyndall effect or Rayleigh scattering. Lord Rayleigh also calculated that even without smoke and dust in the atmosphere, the oxygen and nitrogen molecules would still cause the sky to appear blue because of scattering.
When blue light waves try to go straight through an oxygen and nitrogen molecules, its light is scattered in all directions because of this collision.
This scattered blue light is what makes the sky blue.
All other colors (with longer wavelengths than blue light) are scattered too. Blue light's short wavelength causes it to be scattered the most. (The shorther the wavelength of the color, the more that color gets scattered by the atmosphere) Actually, violet has the shortest wavelength of all colors. Violet is scattered even more than blue light. However, our eyes are much more sensitive to see blue than violet, therefore we see the sky as blue. Very little visible light is absorbed by the atmosphere.
Blue light's short wavelength causes it to get scattered around 10 times more by oxygen and nitrogen molecules than the longer wavelengths (like red) of the other colors visible to us.
The blue in the sky we see is scattered blue light.
A2: Unfortunately, the simple explanation is made a bit more complex by whether you live in the United States or in the United Kingdom. If you live in the United States:
The ocean is blue because pure, clear water has a VERY light blue color.
If you live in the United Kingdom:
The ocean is blue because pure, clear water has a VERY light blue colour.
If you live anywhere else, you unfortunately have to decide for yourself which of these 2 explanations are correct. On a cloudy day when the sky appears grey, the ocean appears gray too (it reflects the sky). High concentrations of plankton make the ocean appear blue-green.
A3: Light from the sun has to travel through much more atmosphere compared to when the sun is overhead from us.
Blue light and all the other colors are scattered around (and diluted) so much by all this atmosphere that only red, orange and yellow light remains visible. Light is not scattered just by the atmosphere itself (oxygen and nitrogen). It is more correct to say that light is scattered by the particles in the atmosphere. The particles in the atmosphere are mainly:
oxygen, nitrogen; clouds containing: liquid water, water vapor (water in gas from), ice (frozen water) snow (water in gas form that is frozen). pollution. (Red, orange and yellow light has the longest wavelengths and is least affected by 'bumping' into oxygen atoms in the atmosphere.)
The red, orange and yellow you see at sunsets reached your eyes more or less in a straight line directly from the sun. By comparison, the blue sky is from billions of scattered (bounced around) reflections of blue light coming from all directions.
A4: Water and ice in clouds scatter all color wavelengths by the same amount. All colors are represented in this scattered light and clouds therefore appears white. (White light is made up of all colors, red, blue, violet, etc.) All wavelengths of light get scattered equally by drops of water and small clumps of ice.
A5: The planet Mars is red because of the red rusted iron dust particles in its atmosphere. The soil of Mars is red as well. Mars is not red because of scattered light - like on earth. The planet Mars has a much thinner atmosphere. Scattered light is much less of a factor on Mars.
