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Night, or nighttime, is the period of darkness when the Sun is below the horizon. Daylight illuminates one side of the Earth, leaving the other in darkness. The opposite of nighttime is daytime. Earth's rotation causes the appearance of sunrise and sunset. Moonlight, airglow, starlight, and light pollution dimly illuminate night. The duration of day, night, and twilight varies depending on the time of year and the latitude. Night on other celestial bodies is affected by their rotation and . The planets Mercury and Venus have much longer nights than Earth. On Venus, night lasts about 58 Earth days. The Moon's rotation is tidally locked, rotating so that one of the sides of the Moon always faces Earth. Nightfall across portions of the near side of the Moon results in lunar phases visible from Earth.
Organisms respond to the changes brought by nightfall: darkness, increased humidity, and lower temperatures. Their responses include direct reactions and adjustments to governed by an internal Circadian clock. These circadian rhythms, regulated by exposure to light and darkness, affect an organism's behavior and physiology. more active at night are called nocturnal and have adaptations for low light, including different forms of night vision and the heightening of other senses. Diurnal animals are active during the day and sleep at night; mammals, birds, and some others dream while asleep. Fungi respond directly to nightfall and increase their biomass. With some exceptions, fungi do not rely on a biological clock. store energy produced through photosynthesis as starch granules to consume at night. Algae engage in a similar process, and cyanobacteria transition from photosynthesis to nitrogen fixation after sunset. In arid environments like deserts, plants evolved to be more active at night, with many gathering carbon dioxide overnight for daytime photosynthesis. Night-blooming cacti rely on nocturnal such as bats and moths for reproduction. Light pollution disrupts the patterns in ecosystems and is especially harmful to night-flying insects.
Historically, night has been a time of increased danger and insecurity. Many daytime dissipated after sunset. Theft, fights, murders, taboo sexual activities, and accidental deaths all became more frequent due in part to reduced visibility. Despite a reduction in urban dangers, the majority of violent crime is still committed after dark. According to psychologists, the widespread fear of the dark and the night stems from these dangers. The fear remains common to the present day, especially among children.
Cultures have personified night through deities associated with some or all of these aspects of nighttime. The folklore of many cultures contains "creatures of the night", including werewolves, witches, ghosts, and goblins, reflecting societal fears and anxieties. The introduction of artificial lighting extended daytime activities. Major European cities hung lanterns housing candles and oil lamps in the 1600s. Nineteenth-century Gas lighting and created unprecedented illumination. The range of socially acceptable leisure activities expanded, and various industries introduced a night shift. Nightlife, encompassing bars, nightclubs, and cultural venues, has become a significant part of urban culture, contributing to social and political movements.
The word night is derived from the Old English niht. Both words are Germanic and cognates of the German nacht. The terms belong to a family of night words present in nearly all European languages, derived from an Indo-European word, reconstructed as *nekwt. The original root is thought most likely to be *nek-, a term relating to death. According to the nineteenth-century British philologist Walter William Skeat, this root meant 'to perish', 'to disappear', or 'to fail', with night being the point where light ceased and perished. More recently, Roland Pooth has argued for the root term to be understood to mean 'empty' or 'naked', with night being the point where the sky is naked and empty of light. As a result of this early origin, night shares its root with the Latin nox, the root of many English terms connected to the night, such as equinox and nocturnal.
Cognates of day are less widespread. Philologist Ernest Weekley attributed the many related night words to the early practice of measuring time in nights rather than days. The term fortnight, an Old English contraction of "fourteen nights", is a remnant of this ancient custom of measuring time in nights.
The letters "gh" were added to the word to represent the yogh character (Ȝ), unavailable on printing presses imported from continental Europe in the fifteenth and sixteenth centuries. As English speakers ceased to pronounce the yogh, the "gh" became silent. A similar process occurred in many English words, such as light.
Night's duration varies least near the equator. The difference between the shortest and longest night increases approaching the poles. At the equator, night lasts roughly 12 hours throughout the year. Tropics have little difference in the length of day and night. At the 45th parallel, the longest winter night is roughly twice as long as the shortest summer night. Within the , night will last the full 24 hours of the winter solstice. The length of this polar night increases closer to the poles. Utqiagvik, Alaska, the northernmost point in the United States, experiences 65 days of polar night. At the pole itself, polar night lasts 179 days from September to March.
Over a year, there is more daytime than nighttime because of the Sun's size and atmospheric refraction. The Sun is not a single point. Viewed from Earth, the Sun ranges in angular diameter from 31 to 33 arcminutes. When the center of the Sun falls to the western horizon, half of the Sun will still be visible during sunset. Likewise, by the time the center of the Sun rises to the eastern horizon, half of the Sun will already be visible during sunrise. This shortens night by about three minutes in temperate zones. Atmospheric refraction is a larger factor. Refraction bends sunlight over the horizon. On Earth, the Sun remains briefly visible after it has geometrically fallen below the horizon. This shortens night by about six minutes. Scattered, diffuse sunlight remains in the sky after sunset and into twilight.
Twilight, the gradual transition to and from darkness when the Sun is below the horizon, has multiple stages. "Civil" twilight occurs when the Sun is between 0° and 6° below the horizon. Nearby planets like Venus and bright stars like Sirius are visible during this period. "Nautical" twilight continues until the Sun is 12° below the horizon. During nautical twilight, the horizon is visible enough for navigation. "Astronomical" twilight continues until the Sun has sunk 18° below the horizon. Beyond 18°, refracted sunlight is no longer visible. The period when the sun is 18° or more below either horizon is called astronomical night.
Similar to the duration of night itself, the duration of twilight varies according to latitude. At the equator, day quickly transitions to night, while the transition can take weeks near the poles. The duration of twilight is longest at the summer solstice and shortest near the equinoxes. Moonlight, starlight, airglow, and light pollution can dimly illuminate the nighttime, with their diffuse aspects being termed skyglow. The amount of skyglow increases each year due to artificial lighting.
Night varies from planet to planet within the Solar System. Mars's dusty atmosphere causes a lengthy twilight period. The refracted light ranges from purple to blue, often resulting in glowing noctilucent clouds. Venus and Mercury have long nights because of their slow rotational periods. The planet Venus rotates once every 243 Earth days. Because of its unusual retrograde rotation, nights last just over 58 Earth days. The dense greenhouse atmosphere on Venus keeps its surface hot enough to melt lead throughout the night. Its planetary wind system, driven by solar heat, reverses direction from day to night. Venus's winds flow from the equator to the poles on the day side and from the poles to the equator on the night side. On Mercury, the planet closest to the Sun, the temperature drops by over after nightfall.
The day-night cycle is one consideration for planetary habitability or the possibility of extraterrestrial life on distant . In general, shorter nights result in a higher equilibrium temperature for the planet. On an Earth-like planet, longer day-night cycles may increase habitability up to a point. Computer models show that longer nights would affect Hadley circulation, resulting in a cooler, less cloudy planet. Once the rotation speed of a planet slows beyond 1/16 that of Earth, the difference in day-to-night temperature shifts increases dramatically. Some exoplanets, like those of TRAPPIST-1, are Tidal locking. Tidally locked planets have equal rotation and orbital periods, so one side experiences constant day, and the other side constant night. In these situations, astrophysicists believe that life would most likely develop in the twilight zone between the day and night hemispheres.
The compound eyes of insects can see at even lower levels of light. For example, the elephant hawk moth can see in color, including ultraviolet, with only starlight. Nocturnal insects navigate using moonlight, lunar phases, infrared vision, the position of the stars, and the Earth's magnetic field. Artificial lighting disrupts the biorhythms of many animals. Night-flying insects that use the moon for navigation are especially vulnerable to disorientation from increasing levels of artificial lighting. Artificial lights attract many night-flying insects that die from exhaustion and nocturnal predators. Decreases in insect populations disrupt the overall ecosystem because their larvae are a key food source for smaller fish. Dark-sky advocate Paul Bogard described the unnatural migration of night-flying insects from the unlit Nevada desert into Las Vegas as "like sparkling confetti floating in the beam's white column".
Some nocturnal animals have developed other senses to compensate for limited light. Many snakes have a pit organ that senses infrared light and enables them to detect heat. Nocturnal mice possess a vomeronasal organ that enhances their sense of smell. Bats heavily depend on echolocation. Echolocation allows an animal to navigate with their sense of hearing by emitting sounds and listening for the time it takes them to bounce back. Bats emit a steady stream of clicks while hunting insects and home in on prey as thin as human hair.
People and other Diurnality animals sleep primarily at night. Humans, other mammals, and birds experience multiple stages of sleep visible via electroencephalography. The stages of sleep are wakefulness, three stages of non-rapid eye movement sleep (NREM), including deep sleep, and rapid eye movement (REM) sleep. During REM sleep, dreams are more frequent and complex. Studies show that some reptiles may also experience REM sleep. During deep sleep, memories are consolidated into long-term memory. Invertebrates most likely experience a form of sleep as well. Studies on bees, which have complex brain structures unrelated to vertebrate brains, have shown improvements in memory after sleep, similar to mammals.
Compared to waking life, dreams are sparse with limited sensory detail. Dreams are hallucinatory or bizarre, and they often have a narrative structure. Many hypotheses exist to explain the function of dreams without a definitive answer. are dreams that cause distress. The word "night-mare" originally referred to nocturnal demons that were believed to assail sleeping dreamers, like the incubus (male) or succubus (female). It was believed that the demons could sit upon a dreamer's chest to suffocate a victim, as depicted in John Henry Fuseli's The Nightmare.
, including cacti, have adapted to the limited water availability in arid environments like . The of cacti do not open until night. When the temperature drops, the pores open to allow the cacti to store carbon dioxide for photosynthesis the next day, a process known as crassulacean acid metabolism (CAM). Cacti and night-blooming plants use CAM to store up to 99% of the carbon dioxide they use in daily photosynthesis. Ceroid cactus often have flowers that bloom at night and fade before sunrise. As few bees are nocturnal, night-flowering plants rely on other pollinators, including moths, beetles, and bats. These flowers rely more on the pollinators' sense of smell, with strong perfumes to attract moths and foul-smelling odors to attract bats.
Eukaryote and Prokaryote organisms that engage in photosynthesis are also affected by nightfall. Like plants, algae will switch to taking in oxygen and processing energy stored as starch. Cyanobacteria switch from photosynthesis to nitrogen fixation after sunset. They also absorb genetic material from their environment at a higher rate during the night.
Dangers increased due to lower visibility. Injuries and deaths were caused by drowning and falling into pits, ditches, and shafts. People were less able to evaluate others after dark. Due to nocturnal alcohol consumption and the anonymity of darkness, quarrels were more likely to escalate to violence. For example, in medieval Stockholm, the majority of murders were committed while intoxicated.
Crime and fear of crime increased at night. In pre-industrial Europe, criminals disguised themselves with hats, face paint, or cloaks. Thieves would trip pedestrians with ropes laid across streets and dismount horse riders using long poles extended from the roadside shadows. They used "dark lanterns" where light could be shined through a single side. Most nocturnal thieves worked alone; organized criminal gangs were uncommon except for burglary. With members numbering into the dozens and hundreds, burglary rings hacked, cut, smashed, and burrowed into homes when residents were sleeping. They used a range of brutality to subdue and intimidate the residents, with the French chauffeurs infamously torturing victims with fire. With nothing comparable to a modern police force, these burglary gangs then escaped into the night, often disguised as demons, ghosts, or monsters. Burglary rings also employed arson both to create distraction and to flush people from their locked homes.
Early sources of heat and illumination (such as chimneys, candles, and oil lamps) created inherent fire risks while families slept. Additionally, bakers and brewers kept fires constantly burning near stacks of wood and charcoal. Cities and towns regularly burned to the ground. One English town, Stratford-upon-Avon, was consumed by fire four times in five years. The increased humidity of night was deemed the result of vapors and fumes. The annual movements of stars and across the night sky were used to track the passage of time, but other changes in the night sky were interpreted as significant .
Many daytime religious, governmental, and local dissipated after nightfall. Fortified Christian communities announced the coming darkness with horns, , or drums. This alerted residents—like peasants working in the fields—to return home before the shut. The English engaged in a daily process of "shutting in", where valuables were brought into homes before they were bolted, barred, locked, and shuttered. Many English and European towns attempted to impose curfews during the medieval period and gradually loosened the restrictions via exceptions. Prayer and Folk religion were more common by night. were hung to ward off nightmares, spells were cast against thievery, and pig hearts were hung in chimneys to block demons from traveling down them. The common phrase "good night" has been shortened from "God give you a good night." In Ottoman Istanbul, the royal palaces shifted to projecting nocturnal power through large parties lit by lanterns, candles, and fireworks. Though Khamr, after dark, Turkish Muslims went to bars and taverns beyond the Muslim areas.
The night has long been a time of increased sexual activity, especially in taboo forms such as Premarital sex, Extramarital sex, gay, and lesbian sex. In colonial New England courtship, young unmarried couples practiced bundling before marriage. The couples would lie down in the woman's bed, her family would wrap them tightly with blankets, and they would spend the night together this way. Some families took precautions to prevent unintended pregnancies, like sleeping in the same room, laying a large wooden board between the couple, or pulling a single stocking over both of their daughter's legs. Historian Roger Ekirch described pre-industrial night as a "sanctuary from ordinary existence."
Artificial lighting expanded the scope of acceptable work and leisure after dark. In the 1600s, the major European cities introduced . These were lit by lamplighters each evening outside of the summer months. Early streetlights were metal and glass enclosures housing candles or . They were suspended above streets or mounted on posts. The use of artificial lighting led to an increase in acceptable nightlife. In more rural areas, night remained a period of rest and nocturnal labor. Young adults, the urban poor, prostitutes, and thieves benefited from the anonymity of darkness and frequently smashed the new lanterns. Gas lighting was invented in the 1800s. A gas mantle was over ten times brighter than an oil lamp. Gas lighting was associated with the creation of regular police forces. In England, police departments were tasked with maintaining the gas lights, which became known as "police lamps". Daytime routines were further pushed back into the night by the Electric light—invented in the late 19th century—and the widespread usage of newer timekeeping devices like watches. Electric lights created for traditionally daytime fields, like India's cotton industry, and created opportunities for working adults to attend night school.
Fear of the dark and the night remains widespread and only amounts to a phobia in rare cases. Nighttime fears are especially common among children. These fears are typically mild, and most children grow out of them. About 1 in 5 children have persistent and intense fears that correlate with decreased sleep quality and anxiety for both the child and their family. Lucretius and Aristotle observed a similar fear of the dark more present among children in the classical era, and there are long traditions among various cultures of telling children bedtime stories of bogeymen and villains who prey upon disobedient children.
Among adults, walking alone after dark is a common nighttime fear. It is so common, that have used some variation of the question, "How safe do you feel or would you feel being alone in your neighbourhood after dark?" to gauge a population's fear of crime and victimization. The fear is most strongly reported by women and sexual minorities. A 1975 study found that the most common nighttime fears expressed by women were murder and sexual assault. Despite most urban crimes correlating to daytime hours of peak activity, violent crime remains most common after dark.
Many cultures have personified the night. Ratri is the star-covered Hinduism goddess of the night. In the Icelandic Prose Edda, night is embodied by Nótt. Ratri and Nött are goddesses of sleep and rest, but it's common for personifications to be associated with misfortune. In Aztec mythology, Tezcatlipoca, the "Night Wind", was associated with obsidian and the nocturnal jaguar. In his "Precious Owl" manifestation, the Aztecs regarded Tezcatlipoca as the bringer of death and destruction. The Aztecs anticipated an unending night when the Tzitzimitl, skeletal female star deities, would descend to consume all humans. In classical mythology, the night goddess Nyx is the mother of Hypnos, Thanatos, Disease, Strife, and Moros. In Jewish culture and Jewish mysticism, the demon Lilith embodies the emotional reactions to darkness, including terror, lust, and liberation.
Nighttime in the pre-industrial period, often called the "night season", was associated with darkness and uncertainty. Various cultures have regarded the night as a time when ghosts and other spirits are active on Earth. When Protestant theologians abandoned the concept of purgatory, many came to view reported ghost sightings as the result of demonic activity. In the sixteenth century, Swiss theologian Ludwig Lavater began attempting to explain reported spirits as mistakes, deceit, or the work of demons. The idea of night as a dangerous, dark, or haunted time persists in modern like the vanishing hitchhiker.
In folklore, nocturnal preternatural beings like , fairies, werewolves, pucks, brownies, , and have overlapping but non-synonymous definitions. The werewolf—and its francophone variations, the loup-garou and rougarou—were believed to be people who transformed into beasts at night. In West Africa and among the African diaspora, there is a widespread tradition of a type of vampire who removes their human skin at night and travels as a blood-sucking ball of light. Variation includes the fifollet, the Surinamese asema, the Caribbean Soucouyant, the Ashanti obayifo, and the Ghanaian asanbosam. The medieval fear of night-flying European witches was influenced by the Roman strix. The Romans described the strix as capable of changing between a beautiful woman and an owl-shaped monster. Common themes among these mythical nocturnal entities include hypersexuality, predation, shapeshifting, deception, mischief, and malice.
Social movements in the 20th century, including feminism, black activism, the gay rights movement, and community action, blurred the lines between political action and broader cultural activities, making political movements a part of the nightlife. Sociologists have argued that vibrant city nightlife scenes contribute to the development of culture and political movements. David Grazian cites as examples the development of beat poetry, musical styles including bebop, urban blues, and early rock, and the importance of nightlife for the development of the gay rights movement in the United States kicked off by the Stonewall riots in Greenwich Village, Lower Manhattan, New York City. Modern cities treat nightlife as necessary to the city's marketability but also something to be managed in order to reduce activities viewed as disorderly, risky, or otherwise problematic. Urban renewal policies have increased the available possibilities for nighttime consumers and decreased the non-commercial nocturnal activities outside of sanctioned festivals and concerts.
Since the Age of Enlightenment, nocturnal settings have been a frequent place for passionate chaos as a counterbalance to the rationality present during the day. In Gothic fiction, this absence of rationality offered a space for lust and terror. Ottoman literature portrayed night as a time for forbidden or unrequited love. Night and day were long depicted as opposite conditions. The electric light, the industrial revolution, and shift work brought many aspects of daily life into the night. The author Charles Dickens lived in London during the time of gas lighting and compared the unstable separation between the waking and sleeping city to the unstable separation he perceived between dream and delusion. Night in contemporary literature offers liminal settings, such as hospitals and gas stations, that contain some aspects of daily life.
Night photography can capture the natural colors of night by increasing the shutter speed, or length of time captured in the photography. Longer exposures open the possibility for photographers to use light painting to selectively illuminate a scene. Digital photography can also make use of film speed, which increase the sensitivity to light, to take shorter exposure shots. This makes it possible to capture moving subjects without turning their movements into a blur.
Baroque paintings typically used a darker color scheme than previous painting styles in Europe. From the 17th century, darkness took up larger areas of paintings on average. Changes in the chemical composition of the paint itself and the development of new techniques for representing light led to the tenebrism style of painting. Tenebrism used stark, realistic depictions of light contrasted with darkness to create realistic depictions of night and darkness illuminated by moonlight, candles, and lamps. The work of Baroque painters, like Caravaggio, who painted an entire studio black, was influenced by the alchemical concept of "nigredo", or blackness as connected to death and decomposition. Dutch Golden Age painter Rembrandt recreated the dim light cast by early street lighting by layering translucent brown glazes.
Impressionism represented darkness with shades of brown and blue based on the ideas that true black was not present in nature and that black had a deadening effect on the art. Claude Monet notably avoided black paints. Vincent van Gogh used heavy outlines between panes of color in his paintings, inspired by woodblock printing in Japan. This style, called cloisonné after the metalworking technique that embedded glass between dark lines of wire, was adopted by other painters like Paul Gauguin. As night in Europe became more artificially lit, former railway worker John Atkinson Grimshaw became known for his vibrantly lit urban paintings. In the modern era, painters have variously returned to archetypal symbols to capture the awe of night or painted scenes that emphasize how the modern city separates the viewer from the night sky.
Near Eastern artists initially rejected these techniques to depict shadow as hiding aspects of creation in shadows. Mughal Empire painters quickly incorporated techniques to depict night, twilight, and mists. Under Emperor Akbar, European materials and techniques were imported. Rajput painting combined these with traditional styles and symbolism. , depictions of women seeking romantic love, were a common subject and often included night as the setting for romance and peril. Jesuit painter Giuseppe Castiglione brought Renaissance techniques for painting light and shadow to 17th-century China. In pieces like One Hundred Famous Views of Edo, Hiroshige developed techniques to represent shadow and nocturnal light that became widespread in Japanese Meiji-era art. Known for his crowd scenes lit by fireworks, Hiroshige had a strong influence on European painters.
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