The shadow of the solid Earth cast on to distant objects (such as mountain-tops) or the atmosphere itself, and visible at sunrise or sunset. It takes the form of a blue-grey segment, normally with a red upper border (known as the counterglow), that rises in the east as the Sun sets in the west. It gradually darkens as it rises until it merges with the dark sky overhead. The reversed sequence is seen at sunrise. See also alpine glow.
Subjects: Meteorology and Climatology.