Sea ice terminology. Describes the thin places in an ice canopy, usually less than 1 meter thick, that appear from below as light, translucent patches in dark surroundings. The under surface of skylig
hts are normally flat. They are termed small or large; if they are big enough for a submarine to attempt to surface through them (120 meters wide or more) they qualify as large.
From the point of view of the submariner, thin places in the ice canopy, usually less than 3 ft (1 m) thick and appearing from below as relatively light, translucent patches in dark surroundings. The
undersurface of a skylight is normally flat. Skylights are called large if big enough for a submarine to attempt to surface through them, or small if not.