Why does the sky turn orange during wildfires?

Smoke from large wildfires releases enormous quantities of fine particulate matter, including ash and soot. These particles are the right size to scatter shorter wavelengths of light (blue and violet) more effectively through Mie scattering, while longer wavelengths (red and orange) pass through with less deflection. When a dense smoke layer hangs overhead, it filters sunlight so strongly that only the reddest light reaches the ground, sometimes turning midday skies a deep orange or even an apocalyptic red. The effect is similar to why sunsets are red, but wildfire smoke can create it at any time of day when thick enough.