Why blue - not red, purple, orange or green? In the middle of a bright, sunny day, the sky is usually a blue.
If you see light from the sun hitting the ground it probably looks like plain white light. However, that white light is made up of all the colors of the rainbow. You can actually separate and see all these colors if you shine sunlight through a specially shaped crystal called a prism. Light energy travels in waves. And diiferent colors of light are created by different types of waves. For example, when our eyes recognize the color red, what we are actually seeing is long, stretched-out light waves with peaks that are far apart. And when our eyes recognize the color blue, we are really seeing shorer, choppier light waves with peaks that are close together. The different colors of light are all determined by how stretched out the light waves are. Together, all the colors make up the spectrum of visible light - the light we can see.
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So, why do we only see blue light when we look up in the sky on a sunny day?
The blue color we see comes from sunlight hitting Earth's atmosphere - a layer of gases that gives us air to breathe and keeps the planet warn enough to live on. When sunlight reaches Earth's atmosphere, it is scattered in all direction bt the gases in the air. The types of gaes in Earth's atmosphere mostly scattter the shorter, choppier waves of blue light. So, when we see a blue sky, we are really just seeing of these blue light waves scattering in our atmosphere.
But wait a minute: why is the sky a different color at sunset?
Well, as the Sun gets lover in the sky, its light is passing through more of the atmosphere to reach you. So, even more of the blue light is scattered away before it hets to you. This allows more of the orange and yellow light to pass straight through the atmosphere and directly to eyes. However if the whole sky glowing red, it could be due to particles of dust, pollution or smoke in the air. These particles also scatter lots of blue light, which can lead to a very red sky.