Afterglow

An afterglow is a broad arch of whitish or pinkish light in the twilight sky after sunset, made up of a purple light and a bright segment beneath it. The purple light appears while the sun is 2 to 6 degrees below the horizon, during civil twilight, and the bright segment continues into nautical twilight; both come from sunlight scattering through atmospheric particles, with red light still visible by scattering and blue light scattering broadly across the sky, the two combining into the characteristic purple color. Volcanic eruptions can intensify the effect by adding fine particulates to the atmosphere, producing especially vivid displays sometimes called volcanic purple light.