Atmospheric optics
![A colorful sky is often due to scattering of light off particulates and pollution, as in this photograph of a sunset during the October 2007 California wildfires.](/Images/godic/202501/27/Firesunset2edit0819.jpg")
![Comparison between the relative sizes of the Moon and a cloud at different points in the sky](/Images/godic/202501/27/Moon_size_illusion0819.png")
![When seen from altitude, as here from an airplane, the sky's color varies from pale to dark at elevations approaching the zenith](/Images/godic/202501/27/Skyshot0819.jpg")
![Purple sky on the La Silla Observatory.[11]](/Images/godic/202501/27/Three_Pillars_of_Astronomy0819.jpg")
Atmospheric optics deals with how the unique optical properties of the Earth's atmosphere cause a wide range of spectacular optical phenomena. The blue color of the sky is a direct result of Rayleigh scattering which redirects higher frequency (blue) sunlight back into the field of view of the observer. Because blue light is scattered more easily than red light, the sun takes on a reddish hue when it is observed through a thick atmosphere, as during a sunrise or sunset. Additional particulate matter in the sky can scatter different colors at different angles creating colorful glowing skies at dusk and dawn. Scattering off of ice crystals and other particles in the atmosphere are responsible for halos, afterglows, coronas, rays of sunlight, and sun dogs. The variation in these kinds of phenomena is due to different particle sizes and geometries.