Alpenglow - Definition and Overview

Alpenglow (German: Alpenglühen) is an optical phenomenon. When the Sun sets in the west, a horizontal red glowing band can sometimes be observed in the east. In mountainous areas such as the Alps, this can be caused by snow, moisture, and ice on mountain sides which receive the scattered red light from the setting Sun.

In the absence of mountains, the aerosols in the eastern part of the sky themselves can still be illuminated in the same way by the remaining red scattered light straddling the border of the Earth's own shadow (the terminator). This back-scattered light produces a red band above the darkness rising in the east. The difference with gegenschein, which is also found in the east, is that alpenglow is caused inside the Earth's atmosphere.