When the sunlight enters our atmosphere, its waves collide with gas molecules. The longer wavelengths, like red and yellow, pass straight through it. But the shorter wavelengths, like blue, collide with the gas molecules and scatter in all directions. Some of the blue light still makes it through directly, but the rest is reflected back to our eyes from all directions. Since the blue light gets reflected from all directions, the whole sky looks blue.
Why is the sky blue in colour?
