Crepuscular rays are alternating light and dark sun rays streaming through gaps in clouds. They appear to fan out from the Sun's position, although they are actually parallel (like the apparent converging of railroad tracks when you look down a long straight track), and arise when clouds cast shadows on to the atmosphere. If the sun is low they might as well cast shadows from distant hills or mountains or a single thunderstorm cloud. The beams of sunlight are made visible by haze in the atmosphere. They are most noticeable when considerable scattering is present, caused by airborne dust, inorganic salts, organic aerosol particles, small water droplets and the air molecules themselves.
When the sun is low, towards twilight (from which the rays derive their name) the light rays often appear reddish, whereas the dark shadows have a green tinge. In rare cases, they extend across the entire sky and anticrepuscular rays converge at the point opposite