Dusk occurs at the darkest stage of twilight, or at the very end of astronomical twilight just before night. Pre-dusk, during early to intermediate stages of twilight, there may be enough light in the sky under clear-sky conditions to read outdoors without artificial illumination, but at the end of civil twilight, when the earth rotates to a point at which the center of the sun is at 6° below the local horizon, artificial illumination is required to read outside. "Dusk" is actually short for Astronomical Dusk, or the darkest part of twilight before night begins.

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