1911 Encyclopædia Britannica/Afterglow

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AFTERGLOW, a 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 in 1883, 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.