We had an incredible sunset tonight. What caused the sun to look like this?
The short answer is that the dimming and red color are being caused by smoke from a wildfire that is about 70 miles away, but there is more to it than that. Sunsets are often red because of Rayleigh scattering. As sunlight passes through our atmosphere, the blue end of the spectrum is partially scattered by the molecules in the air. This causes the sky to look blue, and sunsets to look orange and red. The redness caused by the smoke is due to the Tyndall effect. Instead of the light being scattered by molecules in the air, in this case the light is scattered by tiny particles of smoke. You get basically the same result, but the process is a bit different.