Romantic. Enchanting. Calming. However you view a sunset, they are one of the most beautiful and spectacular atmospheric phenomena around and the opportunity to see one exists every single day of the year.
But why does the sky glow a brilliant red, orange, and yellow combination when the sun sets in the west? What causes it to be even more brilliantly red when forest fires are nearby and smoke is in the air?
It is all due to scattering, Rayleigh scattering to be exact. The same process that causes the sky to be blue is the same process that causes sunsets to be red.
As the sun sets sunlight has to travel through a greater portion of the atmosphere compared to when it is noon. Because it has to travel through a greater amount of atmosphere, the sunlight (which is white meaning it contains all colors) comes into contact with more aerosols in the atmosphere.
Dust, gas molecules, soot, and pollution all contribute to the aerosols and cause the blue and green light from sunlight to be scattered. The reds, oranges, and yellows are less likely to be scattered due to their wavelength and are able to reach our eyes.
The reason for more extremely red sunsets during smoke-filled skies is simply that forest fires add many more aerosols into the atmosphere which scatter most of the blues, greens, yellows, and oranges from the sunlight penetrating the sky and leaving mainly red for our eyes to see.
Neil Opperman
Meteorologist/Weather Producer
