Dusk is the darkest stage of twilight in the evening. 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. Civil dusk occurs when the earth rotates to a point at which the center of the sun is at 6° below the local horizon. This marks the end of the evening civil twilight, the point where artificial illumination is required to read outside. Twilight comes after sunset, which is the point at which the earth has rotated just enough for the sun to be no longer visible on the local horizon (under clear conditions).