Sunset with green flash. The sun has a distorted solar disc and the beginnings of a green flash (top edge of the disc) as it sets below the horizon. The distortions are the result of sunlight refraction, where the different temperatures and densities of moving air refracts the sunlight as it passes through. The green flash is a rare sunset phenomenon that occurs when the atmosphere is especially transparent. This green flash is occurring because the surface of the land where the sun is being viewed is warmer than the air above it, placing blue and green images of the sun slightly higher than the yellow and red.