is the broad high arch of whitish or rosy light appearing occasionally in the sky
above the highest clouds
in the hour of deepening twilight, or reflected
from the high snowfields in mountain
regions long after sunset
. The phenomenon is due to very fine particles of dust
suspended in the high regions of the atmosphere
that produce a scattering effect upon the component parts of white light
. After the eruption of Krakatoa
, a remarkable series of red
sunsets appeared all over the world. These were due to an enormous amount of exceedingly fine dust blown to a great height by that terrific explosion, and then universally diffused by the high atmospheric currents.
Dust particles cause other similar phenomenona, like the Gegenschein.
- (from an old encyclopedia)