Sunlight is made of many colors
What looks like white sunlight contains a range of colors. Each color corresponds to light with a different wavelength. Blue light has a shorter wavelength than red light. When sunlight enters the atmosphere, it meets oxygen, nitrogen, and other particles rather than passing through completely untouched.
What the air does to light
Small molecules in the atmosphere scatter shorter wavelengths particularly efficiently. This process is called Rayleigh scattering. Because blue light is scattered into many different directions, you can see it even when you are not looking directly toward the Sun. This helps explain the blue appearance of a clear daytime sky.
Why sunsets look different
Near sunset, light from the Sun travels through a longer path in the atmosphere. More of the shorter-wavelength light is scattered away from the direct line of sight, so warm yellows, oranges, and reds become more prominent. Dust, haze, and other particles can change the exact colors you observe.
What to remember
The sky is not painted blue, and the air does not act like a blue filter. The color comes from sunlight interacting with the atmosphere and from the directions in which scattered light reaches your eyes.
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