The sky looks blue because of a process called Rayleigh scattering. Here's a step-by-step explanation suitable for a 15-year-old:
- Sunlight and its Colors: Sunlight might look white, but it is actually made up of many colors combined together—red, orange, yellow, green, blue, indigo, and violet. These colors are what we see in a rainbow.
- How Light Travels: When sunlight enters the Earth’s atmosphere, it collides with molecules in the air like nitrogen and oxygen.
- Scattering of Light: The colors of light have different wavelengths. Blue and violet light have shorter wavelengths, while red and orange have longer wavelengths.
- Rayleigh Scattering Effect: The shorter wavelengths (blue and violet) scatter more because they bounce off air molecules in all directions more than the longer wavelengths do.
- Why We See Blue More: Although violet light scatters even more than blue, our eyes are less sensitive to violet, and some of it is absorbed by the upper atmosphere. This means the sky appears mostly blue to us during the day.
- During Sunrise and Sunset: The sun is lower in the sky, so its light passes through more atmosphere, scattering away most of the blue light and leaving red and orange colors to dominate, which is why the sky looks red or orange then.
In short, the sky is blue because blue light scatters more than other colors as sunlight passes through Earth’s atmosphere.