Dusk is the darkest stage of twilight in the evening. 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.

https://en.wikipedia.org/wiki/Dusk

"There are all kinds of interesting questions that come from a knowledge of science, which only adds to the excitement and mystery and awe of a flower."
Richard Feynman
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