The sky appears blue due to a phenomenon called Rayleigh scattering. When sunlight reaches the Earth's atmosphere, it is made up of different colors, or wavelengths, of light. Blue light has shorter wavelengths compared to other colors like red and orange.
As sunlight enters the atmosphere, the molecules in the air scatter the light. The smaller molecules, such as nitrogen and oxygen, scatter shorter wavelengths of light (blue and violet) more effectively than longer wavelengths (red and orange). This is because the shorter wavelengths interact more with the molecules.
So, when sunlight interacts with the Earth's atmosphere, the blue light gets scattered in all directions. This scattered blue light then reaches our eyes from all directions, making the sky appear blue.
To further understand this phenomenon, think of it like this: Imagine you have a glass of water with a few drops of food coloring. When you shine a flashlight through the water, the light scatters, making the water appear colored. The same principle applies to the sky, where the scattering of blue light makes it appear blue to our eyes.
It's important to note that the sky may appear different colors at sunrise or sunset. This is because the sunlight has to pass through more of the Earth's atmosphere at these angles, and the shorter blue and violet wavelengths get scattered even more. As a result, the longer wavelengths, such as red and orange, dominate the sky's color, giving it a warm, reddish appearance.