A soft light that remains in the sky after sunset or after a bright light source has dimmed, or a warm satisfied feeling after something pleasant has ended.
From 'after' (Old English 'æfter') and 'glow' (Old English 'glōwan', of uncertain origin, possibly imitative). Popularized in the 19th century as both a scientific and romantic term.
The afterglow lasts longer after sunset on days with dust or pollution in the air because those particles scatter and reflect light—which is why particularly beautiful sunsets sometimes mean tomorrow might be smoky or hazy.
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