Thus, at the last moments of a sunset we can get a green image of the upper edge of the sun: the green flash. (scientificamerican.com)
Therefore, the outer edge of the photosphere looks dark, an effect called limb darkening that accounts for the clear crisp edge of the sun's surface. (science.howstuffworks.com)
Reflective strips at the edge of the sun canopy increase safety on the streets through better visibility. (kiddyusa.com)