Why does the sunset look red?
Short answer
At sunset, sunlight travels through more atmosphere than it does at midday. Blue light is scattered along the way, so more red and orange light reaches the eye.
How it works
The longer path scatters more short-wavelength light. Dust and smoke can make the colors stronger, although the effect depends on the particles present.
Key point
The practical point is this: Dust and smoke can make the colors stronger, although the effect depends on the particles present.