Detached clouds in the form of white, delicate filaments, mostly in patches or narrow bands. They may have a fibrous (hair-like) and/or silky sheen appearance. Cirrus clouds are always composed of ice crystals, and their transparent character depends upon the degree of separation of the crystals. As a rule, when these clouds cross the sun's disk, they hardly diminish its brightness. When they are exceptionally thick, they may veil its light and obscure its contour. Before sunrise and after sunset, cirrus are often coloured bright yellow or red. These clouds are lit up long before other clouds and fade out much later; some time after sunset they become grey. At all hours of the day, cirrus near the horizon are often of a yellowish colour. This is due to the distance the light travels through the atmosphere at a low angle.
Thin and white, these clouds look like a patchy sheet or layer arranged somewhat-regularly into grains or ripples without shading. Most of these elements have an apparent width of less than one degree (approximately width of the little finger held at arm's length). Predominantly made of ice crystals, cirrocumulus often form in connection with cirrus or cirrostratus or from a degraded state of these cloud types and are short-lived.
Transparent, whitish veil-like clouds with a fibrous (hair-like) or smooth appearance. A sheet of cirrostratus is very extensive and can cover the whole sky. During the day, when the sun is sufficiently high above the horizon, the sheet is never thick enough to prevent shadows of objects on the ground. A veil of cirrostratus may have a similar appearance to a milky veil of fog (or thin stratus), but is distinguished by a halo phenomena nearly always produced around the Sun or Moon shining through a layer of cirrostratus.
