1. Why is the sky blue ?
Katarína Spišáková

2. It's easy to see that the sky is blue. Have you ever wondered why
It's easy to see that the sky is blue. Have you ever wondered why? A lot of other smart people have, too. And it took a long time to figure it out!
The light from the sun looks white. But it is really made up of all the colors of the rainbow.

3. When white light shines through a prism, the light is separated into all its colors. A prism is a specially shaped crystal.
If you visited The Land of the Magic Windows, you learned that the light you see is just one tiny bit of all the kinds of light energy beaming around the universe--and around you! 
Like energy passing through the ocean, light energy travels in waves, too. Some light travels in short, "choppy" waves. Other light travels in long, lazy waves. Blue light waves are shorter than red light waves. 

4. All light travels in a straight line unless something gets in the way and does one of these things:
- reflect it (like a mirror)
- bend it (like a prism)
- or scatter it (like molecules of the gases in the atmosphere)

5. Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time

6. Closer to the horizon, the sky fades to a lighter blue or white
Closer to the horizon, the sky fades to a lighter blue or white. The sunlight reaching us from low in the sky has passed through even more air than the sunlight reaching us from overhead. As the sunlight has passed through all this air, the air molecules have scattered and rescattered the blue light many times in many directions. 
Also, the surface of Earth has reflected and scattered the light. All this scattering mixes the colors together again so we see more white and less blue.

7. What makes a red sunset?
As the sun gets lower in the sky, its light is passing through more of the atmosphere to reach you. Even more of the blue light is scattered, allowing the reds and yellows to pass straight through to your eyes.

8. Sometimes the whole western sky seems to glow
Sometimes the whole western sky seems to glow. The sky appears red because larger particles of dust, pollution, and water vapor in the atmosphere reflect and scatter more of the reds and yellows.

9. After days of rain, a patch of blue sky is a sight for sore eyes
After days of rain, a patch of blue sky is a sight for sore eyes. But why is the sky blue?
Let’s start with the Sun. Light from the Sun appears white but it actually consists of many different colours. We can see these different colours of light in a rainbow or when white light passes through prism. As the white light from the Sun travels through the Earth’s atmosphere, it collides with particles of air. The different colours, or wavelengths, of light are scattered by these collisions by different amounts. Blue light (shorter wavelengh) is scattered more than red light (longer wavelength).
So, when the Sun is high in the sky, blue light is scattered in all directions as sunlight passes through the atmosphere and we see the sky as blue.

10. But it’s a different case when the Sun is close to the horizon at sunset or sunrise. Sunlight from the low Sun has to pass through much more atmosphere before it reaches your eyes meaning most of the blue light has already been scattered leaving just the red. The result is the beautiful colours we see at sunset and sunrise and, very occasionally, a flash of green light.

11. When we see a rainbow we can see a range of colours from red (longer wavelength) through yellows and greens to blues and eventually violet (shorter wavelengths). So if shorter wavelengths are more easily scattered why don't we see the sky as purple?

12. The answer lies with how our eyes react to light
The answer lies with how our eyes react to light. Inside the eye there are two types of cells that react to light. 'Rods' are sensitive to brightness and three types of 'cones' are responsible for detecting colour. The three types of cones are sensitive to lights of certain wavelengths.
The 'blue' cones are more sensitive to blue than violet, so when you look up at the sky, the cones tell your brain you are seeing blue even though there is violet there.

13. Zdroj : Texty : spaceplace.nasa.gov , physics.org
Obrázky: physics.org

14. Thank you for your attention ! 