1. Afterglow may refer to a broad glowing arc, sometimes seen high in the western sky at twilight, caused by fine particles of dust scattering light in the upper atmosphere.
2. Afterglow may also mean lingering radiation, also called postluminescence, that remains after an event such as a gamma-ray burst (which has an X-ray afterglow) or the Big Bang (the afterglow of which is the cosmic microwave background radiation). The term is also used as an alternative name for phosphorescence.