Night

Night is the part of the day when the sun is below the horizon, causing darkness to fall on part of the Earth. It begins when the sun sets and ends when it rises.

Night occurs because the Earth rotates on its axis. At any given moment, one side of the Earth faces the sun (day), while the other side faces away from it (night). This rotation takes approximately 24 hours.

Length of night

The length of night varies by location. In areas near the equator, night and day remain roughly equal throughout the year. Moving toward the polar regions, the difference increases: during winter nights are long, while in summer they are short. At the highest latitudes in the north and south, there are periods when the sun does not set or does not rise.

Twilight

Before and after complete night, there is a period called twilight, when the sun is below the horizon but its light still illuminates the upper atmosphere. Stars appear in stages depending on how far the sun has descended below the horizon. Astronomical night is when the sun's light is completely absent.

Effects on life

The alternation of day and night underlies the circadian rhythm in humans and other organisms. Darkness can trigger the release of melatonin, which is associated with sleep. Many animals are nocturnal, including bats and certain predators.

Culture and religion

Night holds special significance in many cultures. In Islam, the moon and night form the basis of the lunar calendar, and there are prayers and practices performed at night. Modern urban lighting has created what is known as light pollution, which affects the visibility of stars.