It increases with increasing latitude, especially in summer. During the summer in middle latitudes, twilight adds about 30 minutes of light to each morning and evening for outdoor activities. A green flash light may be seen near the upper rim of a rising or setting sun since light penetrates a thick section of the atmosphere, which bends blue light the most, red light the least. Since the atmosphere selectively scatters blue light, green light reaches us instead. The green flash usually lasts about a second, but could be longer in polar region as reported for 35 minutes in the south polar region.
Halo is a ring of light encircling and extending outward from the sun or moon.
It form when light from the moon or sun is refracted by ice crystals of a cirroform cloud. Halos are typically seen as bright, white rings, however, refractive effects can cause a halo to have color. The second type of halos are quite rare. It form as sunlight is refracted by hexagonal plate-like ice crystals of diameters larger than 30 mm that are slowly falling with a horizontal orientation. The ice crystals behave like tiny prisms, bending and dispersing the sunlight into components colors as it passes through them.