The sky appears blue due to a phenomenon called Rayleigh scattering. When sunlight enters the Earth's atmosphere, it collides with air molecules. Blue light, which has a shorter wavelength, is scattered in all directions more than other colors, making the sky look blue to our eyes. During sunrise and sunset, the sky can change colors, appearing red or orange. This happens because the sunlight passes through more atmosphere, scattering shorter wavelengths and allowing longer wavelengths, like red and orange, to dominate. This effect is also influenced by particles and pollutants in the air.