Off-Topic Why is the sky blue?

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The sky appears blue because of a phenomenon called Rayleigh scattering.

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How It Works:​

1. Sunlight is made up of all colors (red, orange, yellow, green, blue, indigo, and violet).
2. Earth’s atmosphere is filled with gases and tiny particles that scatter sunlight in all directions.
3. Shorter wavelengths (blue and violet) scatter more than longer wavelengths (red and yellow).
4. Even though violet scatters the most, our eyes are more sensitive to blue light, so the sky appears blue to us.

Why Does the Sky Change Colors?​

• Sunrise & Sunset: The sun is lower in the sky, so blue light is scattered away, leaving behind red, orange, and pink hues.
• Cloudy Days: Clouds scatter all wavelengths equally, making the sky appear white or gray.

Why Is the Sky Blue? (Detailed Explanation)​

The sky appears blue due to a scientific phenomenon called Rayleigh scattering. This occurs when sunlight interacts with the gases and particles in Earth's atmosphere, scattering shorter wavelengths of light (blue and violet) more than longer wavelengths (red and yellow).

1. Understanding Sunlight & Colors​

Sunlight, also known as white light, is actually made up of all colors of the spectrum:
Red – Longest wavelength (~700 nm)
Orange
Yellow
Green
Blue
Violet – Shortest wavelength (~400 nm)

Each color has a different wavelength:

• Longer wavelengths (red, orange, yellow) pass through the atmosphere more easily.
• Shorter wavelengths (blue, violet) scatter in all directions when they hit gas molecules in the air.

Since our eyes are more sensitive to blue than violet, we perceive the sky as blue instead of violet.

2. How Rayleigh Scattering Works​

What Is Rayleigh Scattering?​

Rayleigh scattering happens when light interacts with molecules in the atmosphere (mainly oxygen and nitrogen), which are much smaller than the wavelength of light.

• Shorter wavelengths (blue and violet) scatter more than longer wavelengths (red and yellow).
• Blue light gets redirected in all directions, filling the sky.
• While violet scatters even more than blue, our eyes are less sensitive to violet light, and some of it is absorbed by the upper atmosphere.

Result: The sky looks blue!

3. Why Does the Sky Change Colors?​

Why Is the Sky Red at Sunrise & Sunset?​

At sunrise and sunset, the sun is lower on the horizon, meaning:
Sunlight has to travel through more atmosphere.
More blue and violet light scatter away, leaving behind red, orange, and yellow hues.
This is why the sky looks reddish during sunrise and sunset.

Why Do Clouds Look White or Gray?​

Clouds scatter all wavelengths of light equally, which is called Mie scattering. Since no specific color is scattered more than others, clouds appear white.

• Thicker clouds absorb more light, making them gray or darker.

Why Is the Sky Sometimes White or Hazy?​

On humid or polluted days, particles like dust, water vapor, or smoke scatter all wavelengths more equally, making the sky appear whitish or hazy.

4. Sky Colors on Other Planets​

Moon – No atmosphere, so the sky appears black.
Mars – Thin atmosphere with dust particles, making the sky reddish-brown during the day and blue at sunset.
Neptune & Uranus – Methane in the atmosphere scatters blue and green light, making the sky deep blue or cyan.

5. Fun Facts About the Sky & Rayleigh Scattering​

The deeper the blue of the sky, the cleaner the atmosphere (less pollution or moisture).
Astronauts see a black sky from space because there’s no atmosphere to scatter light.
Some animals, like bees, can see ultraviolet light, so their version of the sky looks different!

Final Summary​

The sky looks blue because of Rayleigh scattering, which causes shorter wavelengths (blue and violet) to scatter more than red and yellow.
Our eyes perceive blue better than violet, so we see a blue sky.
Sunsets appear red because more blue light is scattered away, leaving longer wavelengths like red and orange.