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Twilight is the time between darkness and sunrise in the morning, and sunset and complete darkness in the evening, when there is light outside, but the Sun is below the horizon. There are 3 types of twilight: civil, nautical, and astronomical. Dubai skyline in twilight.
Evening is between sunset and late (10 p.m. or midnight). Night is anywhere from sunset to sunrise (plus or minus 30 minutes). Morning begins at midnight, but dawn doesn't start until almost sunrise. Edit: It's been pointed out that sunset isn't necessarily the hard time for the start of the evening, rather that dusk (or twilight) could be the beginning.