When it sets below the horizon, the sun continues to shine on the atmosphere above the Earth’s surface. The Earth is a sphere, has a deep atmosphere and our sun is around 93 million miles away. If we lived on a flat disc (like our ancestors believed) and the sun brushed the edge of it as it set, it would indeed get night-dark instantly the sun was out of sight. Why is it not dark as soon as the sun sets? If the source of our daylight has gone below the horizon, why does it take so long to actually get dark? Why is it Not Dark as Soon as the Sun Sets? Night gives way to astronomical twilight, then nautical twilight and finally civilian twilight, which ends with the sun rising. The reverse of these phases is true as we head towards sunrise.
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