Night
Biology

Living organisms react directly to the darkness of night. Light and darkness also affect circadian rhythms, the physical and mental changes that occur in a 24-hour cycle. This daily cycle is regulated by an internal " biological clock " that is adjusted by exposure to light. The length and timing of nighttime depend on location and time of year. Organisms that are more active at night possess adaptations to the night's dimmer light, increased humidity, and lower temperatures.
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