Wakefulness is a daily recurring brain state and state of consciousness in which an individual is conscious and engages in coherent cognitive and behavioral responses to the external world.
116-419: Being awake is the opposite of being asleep , in which most external inputs to the brain are excluded from neural processing. The longer the brain has been awake, the greater the synchronous firing rates of cerebral cortex neurons. After sustained periods of sleep, both the speed and synchronicity of the neurons firing are shown to decrease. Another effect of wakefulness is the reduction of glycogen held in
232-587: A night shift . Nightlife , encompassing bars, nightclubs, and cultural venues, has become a significant part of urban culture, contributing to social and political movements. A planet's rotation causes nighttime and daytime . When a place on Earth is pointed away from the Sun, that location experiences night. The Sun appears to set in the West and rise in the East due to Earth's rotation. Many celestial bodies, including
348-903: 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 diurnal 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
464-405: A 24-hour cycle, whereas in monophasic sleep this occurs all at once. Under experimental conditions, humans tend to alternate more frequently between sleep and wakefulness (i.e., exhibit more polyphasic sleep) if they have nothing better to do. Given a 14-hour period of darkness in experimental conditions, humans tended towards bimodal sleep, with two sleep periods concentrated at the beginning and at
580-407: A brain area directly above the optic chiasm , is presently considered the most important nexus for this process; however, secondary clock systems have been found throughout the body. An organism whose circadian clock exhibits a regular rhythm corresponding to outside signals is said to be entrained ; an entrained rhythm persists even if the outside signals suddenly disappear. If an entrained human
696-538: A child's quality of sleep as well as prepare them to make and keep healthy sleep hygiene habits in the future. Children need many hours of sleep per day in order to develop and function properly: up to 18 hours for newborn babies, with a declining rate as a child ages. Early in 2015, after a two-year study, the National Sleep Foundation in the US announced newly revised recommendations as shown in
812-414: A factor which may exacerbate disruption of the circadian cycle. Scientific studies on sleep have shown that sleep stage at awakening is an important factor in amplifying sleep inertia . Determinants of alertness after waking up include quantity/quality of the sleep, physical activity the day prior, a carbohydrate-rich breakfast, and a low blood glucose response to it. Sleep timing is controlled by
928-561: A form of sleep as well. Studies on bees, which have complex but unrelated brain structures, 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. Nightmares are dreams that cause distress. The word "night-mare" originally referred to nocturnal demons that were believed to assail sleeping dreamers, like
1044-616: A full eight hours. Researchers have found that sleeping 6–7 hours each night correlates with longevity and cardiac health in humans, though many underlying factors may be involved in the causality behind this relationship. Sleep difficulties are furthermore associated with psychiatric disorders such as depression , alcoholism , and bipolar disorder . Up to 90 percent of adults with depression are found to have sleep difficulties. Dysregulation detected by EEG includes disturbances in sleep continuity, decreased delta sleep and altered REM patterns with regard to latency, distribution across
1160-407: A function of the amount of time elapsed since the last adequate sleep episode) must be balanced against the circadian element for satisfactory sleep. Along with corresponding messages from the circadian clock, this tells the body it needs to sleep. The timing is correct when the following two circadian markers occur after the middle of the sleep episode and before awakening: maximum concentration of
1276-413: A good night's sleep. The American Academy of Sleep Medicine (AASM) divides NREM into three stages: N1, N2, and N3, the last of which is also called delta sleep or slow-wave sleep . The whole period normally proceeds in the order: N1 → N2 → N3 → N2 → REM. REM sleep occurs as a person returns to stage 2 or 1 from a deep sleep. There is a greater amount of deep sleep (stage N3) earlier in the night, while
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#17327728528541392-482: A greater percentage of rod cells. In most mammals, rod cells contain densely packed DNA near the edge of the nucleus. For nocturnal mammals, this is reversed with the densely packed DNA in the center of the nucleus, which reduces the scattering of light. Some nocturnal animals have a mirror, the tapetum lucidum , behind the retina . This doubles the amount of light their eyes can process. The compound eyes of insects can see at even lower levels of light. For example,
1508-427: A key role in the maintenance of the cortical activation that underlies wakefulness. Several systems originating in this part of the brain control the shift from wakefulness into sleep and sleep into wakefulness. Histamine neurons in the tuberomammillary nucleus and nearby adjacent posterior hypothalamus project to the entire brain and are the most wake-selective system so far identified in the brain. Another key system
1624-796: A large role in the function of the endocrine and immune systems . The internal circadian clock promotes sleep daily at night , when it is dark. The diverse purposes and mechanisms of sleep are the subject of substantial ongoing research. Sleep is a highly conserved behavior across animal evolution, likely going back hundreds of millions of years. Humans may suffer from various sleep disorders , including dyssomnias , such as insomnia , hypersomnia , narcolepsy , and sleep apnea ; parasomnias , such as sleepwalking and rapid eye movement sleep behavior disorder ; bruxism ; and circadian rhythm sleep disorders . The use of artificial light has substantially altered humanity's sleep patterns. Common sources of artificial light include outdoor lighting and
1740-462: A major part of the economy and urban planning in modern cities. People who prefer to be active at night are called night owls . 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
1856-516: A metaphor for nocturnal danger. Roman poets like Marcus Manilius and Aratus worked late into the night and incorporated darkness and the night sky into their writing. 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
1972-496: A much higher rate. Before the industrial era , night was a time of heightened insecurity. Fear of the night was common but varied in intensity across cultures. 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. In medieval Stockholm ,
2088-418: A particular frequency corresponds to various points in the sleep-wake cycle, such as being asleep, being awake, or falling asleep. Alpha, beta, theta, gamma, and delta waves are all seen in the different stages of sleep. Each waveform maintains a different frequency and amplitude. Alpha waves are seen when a person is in a resting state, but is still fully conscious. Their eyes may be closed and all of their body
2204-445: A screen before bed may interfere with sleep. Modern humans often find themselves desynchronized from their internal circadian clock, due to the requirements of work (especially night shifts ), long-distance travel, and the influence of universal indoor lighting. Even if they have sleep debt, or feel sleepy, people can have difficulty staying asleep at the peak of their circadian cycle. Conversely, they can have difficulty waking up in
2320-470: A single side. Gangs were uncommon except for housebreaking . The increased humidity of night was deemed the result of vapors and fumes. The annual movements of stars and constellations across the night sky were used to track the passage of time, but other changes in the night sky were interpreted as significant omens . Many daytime religious, governmental, and local social controls dissipated after nightfall. Fortified Christian communities announced
2436-438: A structured bedtime routine. This can look differently among families, but will generally consist of a set of rituals such as reading a bedtime story, a bath, brushing teeth, and can also include a show of affection from the parent to the child such a hug or kiss before bed. A bedtime routine will also include a consistent time that the child is expected to be in bed ready for sleep. Having a reliable bedtime routine can help improve
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#17327728528542552-611: A subjective point of view. Objective sleep quality refers to how difficult it is for a person to fall asleep and remain in a sleeping state, and how many times they wake up during a single night. Poor sleep quality disrupts the cycle of transition between the different stages of sleep. Subjective sleep quality in turn refers to a sense of being rested and regenerated after awaking from sleep. A study by A. Harvey et al. (2002) found that insomniacs were more demanding in their evaluations of sleep quality than individuals who had no sleep problems. Homeostatic sleep propensity (the need for sleep as
2668-668: 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 fell, while Helga Crane in
2784-540: A transitional period is called slow-wave sleep or deep sleep. During this phase, body temperature and heart rate fall, and the brain uses less energy. REM sleep, also known as paradoxical sleep, represents a smaller portion of total sleep time. It is the main occasion for dreams (or nightmares ), and is associated with desynchronized and fast brain waves, eye movements, loss of muscle tone, and suspension of homeostasis . The sleep cycle of alternate NREM and REM sleep takes an average of 90 minutes, occurring 4–6 times in
2900-411: Is Neurospora crassa , a bread mold, widely used to study biorhythms. During the day, plants engage in photosynthesis and release oxygen . By night, plants engage in respiration , consuming oxygen and releasing carbon dioxide. Plants can draw up more water after sunset, which facilitates new leaf growth. As plants cannot create energy through photosynthesis after sunset, they use energy stored in
3016-522: Is adenosine , a neurotransmitter that inhibits many of the bodily processes associated with wakefulness. Adenosine levels increase in the cortex and basal forebrain during prolonged wakefulness, and decrease during the sleep-recovery period, potentially acting as a homeostatic regulator of sleep. Coffee , tea, and other sources of caffeine temporarily block the effect of adenosine, prolong sleep latency, and reduce total sleep time and quality. Humans are also influenced by aspects of social time , such as
3132-540: Is a marked decrease in muscle activity and interactions with the surrounding environment. While sleep differs from wakefulness in terms of the ability to react to stimuli , it still involves active brain patterns, making it more reactive than a coma or disorders of consciousness . Sleep occurs in repeating periods , during which the body alternates between two distinct modes: REM and non-REM sleep . Although REM stands for "rapid eye movement", this mode of sleep has many other aspects, including virtual paralysis of
3248-557: Is accumulated against an individual's average sleep or some other benchmark. It is also unclear whether the prevalence of sleep debt among adults has changed appreciably in the industrialized world in recent decades. Sleep debt does show some evidence of being cumulative. Subjectively, however, humans seem to reach maximum sleepiness 30 hours after waking. It is likely that in Western societies , children are sleeping less than they previously have. One neurochemical indicator of sleep debt
3364-474: 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, Black 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
3480-399: Is isolated in a bunker with constant light or darkness, he or she will continue to experience rhythmic increases and decreases of body temperature and melatonin, on a period that slightly exceeds 24 hours. Scientists refer to such conditions as free-running of the circadian rhythm. Under natural conditions, light signals regularly adjust this period downward, so that it corresponds better with
3596-450: Is known as a "natural short sleeper". This condition is not to be confused with intentional sleep deprivation, which leaves symptoms such as irritability or temporarily impaired cognitive abilities in people who are predisposed to sleep a normal amount of time but not in people with FNSS. The genes DEC2 , ADRB1 , NPSR1 and GRM1 are implicated in enabling short sleep. The quality of sleep may be evaluated from an objective and
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3712-422: Is observed to be a necessary behavior across most of the animal kingdom, including some of the least cognitively advanced animals which have no need for other functions of sleep, such as memory consolidation or dreaming. It has been widely accepted that sleep must support the formation of long-term memory, and generally increasing previous learning and experiences recalls. However, its benefit seems to depend on
3828-443: Is profoundly influenced by changes in light, since these are its main clues about what time it is. Exposure to even small amounts of light during the night can suppress melatonin secretion, and increase body temperature and wakefulness. Short pulses of light, at the right moment in the circadian cycle, can significantly 'reset' the internal clock. Blue light, in particular, exerts the strongest effect, leading to concerns that use of
3944-400: Is regulated by a process called homeostasis . Induced or perceived lack of sleep is called sleep deprivation . Process S is driven by the depletion of glycogen and accumulation of adenosine in the forebrain that disinhibits the ventrolateral preoptic nucleus , allowing for inhibition of the ascending reticular activating system . Sleep deprivation tends to cause slower brain waves in
4060-443: Is resting and relatively still, where the body is starting to slow down. Beta waves take over alpha waves when a person is at attention, as they might be completing a task or concentrating on something. Beta waves consist of the highest of frequencies and the lowest of amplitude, and occur when a person is fully alert. Gamma waves are seen when a person is highly focused on a task or using all their concentration. Theta waves occur during
4176-543: Is that provided by the orexins (also known as hypocretins) projecting neurons. These exist in areas adjacent to histamine neurons and like them project widely to most brain areas and associate with arousal . Orexin deficiency has been identified as responsible for narcolepsy . Research suggests that orexin and histamine neurons play distinct, but complementary roles in controlling wakefulness with orexin being more involved with wakeful behavior and histamine with cognition and activation of cortical EEG . It has been suggested
4292-519: Is the only extant Greek tragedy where night is explicitly invoked and made an element of the story. In the play, night is a time of disorder and confusion that allows Odysseus to sneak into the Trojan camp and kill King Rhesus of Thrace . The handful of surviving classical Classical Greek texts that describe the nocturnal activities of women portray female freedom especially to speak openly, male anxieties about that freedom, and magic that functions as
4408-518: Is the period of darkness when the Sun is below the horizon . The opposite of nighttime is daytime . Sunlight illuminates one side of the Earth, leaving the other in darkness. 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
4524-519: Is tidally locked to Earth; it rotates so that one side of the Moon always faces the Earth. The side of the Moon facing away from Earth is called the far side of the Moon and the side facing Earth is called the near side of the Moon . During lunar night on the near side, Earth is 50 times brighter than a full moon. Because the Moon has no atmosphere, there is an abrupt transition from day to night without twilight. Night varies from planet to planet within
4640-670: The Aztec personification of the Milky Way. The elongated Egyptian goddess Nut and N!adima from Botswana are said to consume the Sun at dusk. In the Ancient Egyptian religion , the Sun then travels through the netherworld inside Nut's body, where it is reborn at dawn. Many cultures have personified the night. Ratri is the star-covered Hindu goddess of the night. In the Icelandic Prose Edda , night
4756-544: 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 116.75 Earth days. The dense greenhouse atmosphere on Venus keeps its surface hot enough to melt lead throughout
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4872-456: The Tzitzimīmeh , skeletal female star deities, would descend to consume all humans. In classical mythology, the night goddess Nyx is the mother of Sleep , Death , Disease, Strife , and Doom . In Jewish culture and mysticism , the demon Lilith embodies the emotional reactions to darkness including terror, lust, and liberation. Nighttime in the pre-industrial period, often called
4988-399: The astrocytes , which supply energy to the neurons. Studies have shown that one of sleep's underlying functions is to replenish this glycogen energy source. Wakefulness is produced by a complex interaction between multiple neurotransmitter systems arising in the brainstem and ascending through the midbrain , hypothalamus , thalamus and basal forebrain . The posterior hypothalamus plays
5104-424: The central nervous system of their prey, allowing the fungi to control the actions of the dying insect. During the late afternoon, the fungi will pilot their prey to higher elevation where wind currents can carry its spores further. The fungi will kill and digest the insect as night falls, extending fruiting bodies from the host's exoskeleton. Few species of fungi have true circadian rhythms. A notable exception
5220-488: The circadian clock (Process C), sleep-wake homeostasis (Process S), and to some extent by the individual will. Sleep timing depends greatly on hormonal signals from the circadian clock, or Process C, a complex neurochemical system which uses signals from an organism's environment to recreate an internal day–night rhythm. Process C counteracts the homeostatic drive for sleep during the day (in diurnal animals) and augments it at night. The suprachiasmatic nucleus (SCN),
5336-577: 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
5452-419: The fetus is not awake, with wakefulness occurring in the newborn due to the stress of being born and the associated activation of the locus coeruleus . [REDACTED] The dictionary definition of wakefulness at Wiktionary Asleep Sleep is a state of reduced mental and physical activity in which consciousness is altered and certain sensory activity is inhibited. During sleep, there
5568-437: The frontal cortex , shortened attention span, higher anxiety, impaired memory, and a grouchy mood. Conversely, a well-rested organism tends to have improved memory and mood. Neurophysiological and functional imaging studies have demonstrated that frontal regions of the brain are particularly responsive to homeostatic sleep pressure. There is disagreement on how much sleep debt is possible to accumulate, and whether sleep debt
5684-602: 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 . Fungi can sense the presence and absence of light, and the nightly changes of most fungi growth and biological processes are direct responses to either darkness or falling temperatures. By night, fungi are more engaged in synthesizing cellular components and increasing their biomass. For example, fungi that preys on insects will infect
5800-531: 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 feu-follet , Surinamese asema , and Caribbean sukuyan , Ashanti obayifo , and Ghanaian asanbosam . The medieval fear of night-flying European witches
5916-447: 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
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#17327728528546032-446: The 1600s, the major European cities introduced streetlights. These were lit by lamplighters each evening outside of the summer months. Early street lights were metal and glass enclosures housing candles or oil lamps . 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,
6148-546: The Sun and shorter when a hemisphere is tilted toward the Sun. As a result, the longest night of the year for the Northern Hemisphere will be the shortest night of the year for the Southern Hemisphere . 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
6264-490: The background. Lower budget films are more likely to use day for night shooting, larger budget films are more likely to film at night with artificial lighting. Cinematographers have used tinting, filters, color balance settings, and physical lights to color night scenes blue. In low light, people experience the Purkinje effect which causes reds to dim so that more blue is perceived. As light decreases towards total darkness,
6380-405: The body. Dreams are a succession of images, ideas, emotions, and sensations that usually occur involuntarily in the mind during certain stages of sleep. During sleep, most of the body's systems are in an anabolic state, helping to restore the immune , nervous , skeletal , and muscular systems; these are vital processes that maintain mood , memory , and cognitive function , and play
6496-415: The brain and body, the reduced rate of metabolism enables countervailing restorative processes. The brain requires sleep for restoration, whereas these processes can take place during quiescent waking in the rest of the body. The essential function of sleep may be its restorative effect on the brain: "Sleep is of the brain, by the brain and for the brain." This theory is strengthened by the fact that sleep
6612-560: The brain restores its supply of adenosine triphosphate (ATP), the molecule used for short-term storage and transport of energy. In quiet waking, the brain is responsible for 20% of the body's energy use, thus this reduction has a noticeable effect on overall energy consumption. Sleep increases the sensory threshold . In other words, sleeping persons perceive fewer stimuli, but can generally still respond to loud noises and other salient sensory events. During slow-wave sleep , humans secrete bursts of growth hormone . All sleep, even during
6728-478: The changes brought by nightfall, including darkness, increased humidity, and lower temperatures. Their responses include direct reactions and adjustments to circadian rhythms , governed by an internal biological clock . These circadian rhythms, regulated by exposure to light and darkness, affect an organism's behavior and physiology . Animals more active at night are called nocturnal and have adaptations for low light, including different forms of night vision and
6844-453: 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. In literature, night is often associated with mysterious, hidden, dangerous, and clandestine activities. Rhesus
6960-437: The coming darkness with horns, church bells , or drums. This alerted residents—like peasants working the fields—to return home before the city gates 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
7076-809: 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. Animals that are active primarily at night are called nocturnal and usually possess adaptations for night vision. In vertebrates' eyes, two types of photoreceptor cells sense light. Cone cells sense color but are ineffective in low light; rod cells sense only brightness but remain effective in very dim light. The eyes of nocturnal animals have
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#17327728528547192-440: The day in black and white. The sections of the monochrome film reel with exterior night scenes were soaked in an acidic dye, that tinted the whole scene blue. " Day for night " is a set of cinematic techniques that simulate a night scene while filming in daylight. They include underexposing to the soften scene, using a graduated neutral-density filter to mute lighting, and setting up the artificial lighting to amplify shadows in
7308-654: The day, is associated with the secretion of prolactin . Key physiological methods for monitoring and measuring changes during sleep include electroencephalography (EEG) of brain waves , electrooculography (EOG) of eye movements, and electromyography (EMG) of skeletal muscle activity. Simultaneous collection of these measurements is called polysomnography , and can be performed in a specialized sleep laboratory . Sleep researchers also use simplified electrocardiography (EKG) for cardiac activity and actigraphy for motor movements. The electrical activity seen on an EEG represents brain waves. The amplitude of EEG waves at
7424-926: The deepest period of sleep. Napping too long and entering the slow wave cycles can make it difficult to awake from the nap and leave one feeling unrested. This period of drowsiness is called sleep inertia . The siesta habit has recently been associated with a 37% lower coronary mortality, possibly due to reduced cardiovascular stress mediated by daytime sleep. Short naps at mid-day and mild evening exercise were found to be effective for improved sleep, cognitive tasks, and mental health in elderly people. Monozygotic (identical) but not dizygotic (fraternal) twins tend to have similar sleep habits. Neurotransmitters, molecules whose production can be traced to specific genes, are one genetic influence on sleep that can be analyzed. The circadian clock has its own set of genes. Genes which may influence sleep include ABCC9 , DEC2 , Dopamine receptor D2 and variants near PAX 8 and VRK2 . While
7540-640: 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 riots at the Stonewall Inn nightclub in Greenwich Village , Lower Manhattan , New York City . odern cities treat nightlife as necessary to
7656-460: The difference in day to night temperature shifts increases dramatically. Some exoplanets, like those of TRAPPIST-1 , are tidally locked . 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. Living organisms react directly to
7772-514: The end of the dark time. Bimodal sleep in humans was more common before the Industrial Revolution . Different characteristic sleep patterns, such as the familiarly so-called " early bird " and " night owl ", are called chronotypes . Genetics and sex have some influence on chronotype, but so do habits. Chronotype is also liable to change over the course of a person's lifetime. Seven-year-olds are better disposed to wake up early in
7888-558: The end of the sleep cycle. Awakening involves heightened electrical activation in the brain, beginning with the thalamus and spreading throughout the cortex . On a typical night of sleep, there is not much time that is spent in the waking state. In various sleep studies that have been conducted using the electroencephalography, it has been found that females are awake for 0-1% during their nightly sleep while males are awake for 0-2% during that time. In adults, wakefulness increases, especially in later cycles. One study found 3% awake time in
8004-432: 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 illuminates the nighttime, with their diffuse aspects being termed skyglow . The amount of skyglow increases each year due to artificial lighting . Night exists on
8120-486: The exact 24 hours of an Earth day. The circadian clock exerts constant influence on the body, affecting sinusoidal oscillation of body temperature between roughly 36.2 °C and 37.2 °C. The suprachiasmatic nucleus itself shows conspicuous oscillation activity, which intensifies during subjective day (i.e., the part of the rhythm corresponding with daytime, whether accurately or not) and drops to almost nothing during subjective night. The circadian pacemaker in
8236-533: The first ninety-minute sleep cycle, 8% in the second, 10% in the third, 12% in the fourth, and 13–14% in the fifth. Most of this awake time occurred shortly after REM sleep. Today, many humans wake up with an alarm clock ; however, people can also reliably wake themselves up at a specific time with no need for an alarm. Many sleep quite differently on workdays versus days off, a pattern which can lead to chronic circadian desynchronization. Many people regularly look at television and other screens before going to bed,
8352-770: 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. Plants 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 pollinators such as bats and moths for reproduction. Light pollution disrupts
8468-412: The highest rate of sleep. The hours that children spend asleep influence their ability to perform on cognitive tasks. Children who sleep through the night and have few night waking episodes have higher cognitive attainments and easier temperaments than other children. Sleep also influences language development. To test this, researchers taught infants a faux language and observed their recollection of
8584-439: The horizon. During nautical twilight, the horizon is visible enough for navigation. "Astronomical" twilight continues until the Sun has sunk 18 degrees below the horizon. Beyond 18 degrees, refracted sunlight is no longer visible. The period when the sun is 18 or more degrees below either horizon is called astronomical night. Similar to the duration of night itself, the duration of twilight varies according to latitude . At
8700-448: The hormone melatonin, and minimum core body temperature. Human sleep-needs vary by age and amongst individuals; sleep is considered to be adequate when there is no daytime sleepiness or dysfunction. Moreover, self-reported sleep duration is only moderately correlated with actual sleep time as measured by actigraphy , and those affected with sleep state misperception may typically report having slept only four hours despite having slept
8816-475: The hours when other people are awake, the hours when work is required, the time on clocks, etc. Time zones , standard times used to unify the timing for people in the same area, correspond only approximately to the natural rising and setting of the sun. An extreme example of the approximate nature of time zones is China, a country which used to span five time zones and now officially uses only one (UTC+8). In polyphasic sleep , an organism sleeps several times in
8932-441: The human eye has more scotopic vision , relying more rod cells and less able to perceive color. Night photography can capture the natural colors of night by increasing the exposure time , 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 high-ISO settings , which increase
9048-508: The late evening into the early morning. It has traditionally included venues such as pubs , bars , nightclubs , live music , concerts , cabarets , theatre , Hookah lounges , cinemas , and shows. Nightlife entertainment is often more adult -oriented than daytime entertainment. It also includes informal gatherings like parties , botellón , gymkhanas , bingo , and amateur sports. In many cities, there has been an increasing focus on nightlife catering to tourists. Nightlife has become
9164-445: The latitude. Night on other celestial bodies is affected by their rotation and orbital periods . The planets Mercury and Venus have much longer nights than Earth. On Venus, night lasts 120 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
9280-489: The latter have been found in a GWAS study that primarily detects correlations (but not necessarily causation), other genes have been shown to have a more direct effect. For instance, mice lacking dihydropyrimidine dehydrogenase (Dpyd) had 78.4 min less sleep during the lights-off period than wild-type mice. Dpyd encodes the rate-limiting enzyme in the metabolic pathway that catabolizes uracil and thymidine to β- alanine , an inhibitory neurotransmitter . This also supports
9396-639: The limited water availability in arid environments like deserts . The stomata 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 most night-blooming plants use CAM to store up to 99% of the carbon dioxide they use in daily photosynthesis. Ceroid cacti 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
9512-399: 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
9628-422: The middle of the night. Circadian rhythm exerts some influence on the nighttime secretion of growth hormone. The circadian rhythm influences the ideal timing of a restorative sleep episode. Sleepiness increases during the night. REM sleep occurs more during body temperature minimum within the circadian cycle, whereas slow-wave sleep can occur more independently of circadian time. The internal circadian clock
9744-496: The morning than are fifteen-year-olds. Chronotypes far outside the normal range are called circadian rhythm sleep disorders. Naps are short periods of sleep that one might take during the daytime, often in order to get the necessary amount of rest. Napping is often associated with childhood, but around one-third of American adults partake in it daily. The optimal nap duration is around 10–20 minutes, as researchers have proven that it takes at least 30 minutes to enter slow-wave sleep,
9860-405: The night and density of eye movements. Sleep duration can also vary according to season. Up to 90% of people report longer sleep duration in winter, which may lead to more pronounced seasonal affective disorder . By the time infants reach the age of two, their brain size has reached 90 percent of an adult-sized brain; a majority of this brain growth has occurred during the period of life with
9976-749: The night by the electric light bulb —invented in the late 19th century—and the widespread usage of newer timekeeping devices like watches. Electric lights created night shifts for traditionally daytime fields, like India's cotton industry, and created opportunities for working adults to attend night school . Before the widespread usage of artificial lighting, sleep was typically split into two major segments separated by about an hour of wakefulness. During this midnight period, people engaged in prayer, crimes, urination, sex, and, most commonly, reflection. Without exposure to artificial light, studies show that people revert to sleeping in two separate intervals. Diverse cultures have made connections between
10092-493: The night sky and the afterlife . Many Native American peoples have described the Milky Way as a path where the deceased travel as stars. The Lakota term for the Milky Way is Wanáǧi Thacháŋku , or "Spirit's Road". In Mayan mythology, the Milky Way's dark band is the Road of Xibalba , the path to the underworld . Unrelated cultures share a myth of a star-covered sky goddess who arches over the planet after sunset, like Citlālicue ,
10208-427: 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
10324-448: 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 and electric lights created unprecedented illumination. The range of socially acceptable leisure activities expanded, and various industries introduced
10440-412: 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 over 1,000 °F (538 °C) after nightfall. The day-night cycle is one consideration for planetary habitability or
10556-454: The other planets and moons in the solar system. The length of night is affected by the rotation period and orbital period of the celestial object. The lunar phases visible from Earth result from nightfall on the Moon . The Moon has longer nights than Earth, lasting about two weeks. This is half of the synodic lunar month , the time it takes the Moon to cycle through its phases. The Moon
10672-408: The other planets in the solar system, have a form of night. The length of night on Earth varies depending on the time of year. Longer nights occur in winter, with the winter solstice being the longest. Nights are shorter in the summer, with the summer solstice being the shortest. Earth orbits the Sun on an axis tilted 23.44 degrees. Nights are longer when a hemisphere is tilted away from
10788-486: 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
10904-500: 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 social controls dissipated after sunset. Theft, fights, murders, taboo sexual activities, and accidental deaths all became more frequent due in part to reduced visibility. Cultures have personified night through deities associated with some or all of these aspects of nighttime. The folklore of many cultures contains "creatures of
11020-466: The period of a person being awake, and they continue to transition into Stage 1 of sleep and in stage 2. Delta waves are seen in stages 3 and 4 of sleep when a person is in their deepest of sleep. Sleep is divided into two broad types: non-rapid eye movement (non-REM or NREM) sleep and rapid eye movement (REM) sleep. Non-REM and REM sleep are so different that physiologists identify them as distinct behavioral states. Non-REM sleep occurs first and after
11136-406: The phase of sleep and the type of memory. For example, declarative and procedural memory-recall tasks applied over early and late nocturnal sleep, as well as wakefulness controlled conditions, have been shown that declarative memory improves more during early sleep (dominated by SWS) while procedural memory during late sleep (dominated by REM sleep) does so. Night Night or nighttime
11252-523: The plant, typically as starch granules . Plants use this stored energy at a steady rate, depleting their reserves almost right at dawn. Plants will adjust their rate of consumption to match the expected time until sunrise. This avoids prematurely running out of starch reserves, and it allows the plant to adjust for longer nights in the winter. If a plant is subjected to artificially early darkness, it will ration its energy consumption to last until dawn. Succulent plants , including cacti , have adapted to
11368-429: 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 level with the western horizon , half of the Sun will still be visible during sunset. Likewise, by
11484-442: The pollinators' sense of smell with strong perfumes to attract moths and foul-smelling odors to attract bats. Eukaryotic and prokaryotic 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 , also known as blue algae, switch from photosynthesis to nitrogen fixation after sunset, and they absorb DNA at
11600-434: The possibility of extraterrestrial life on distant exoplanets . 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,
11716-451: The proportion of REM sleep increases in the two cycles just before natural awakening. Awakening can mean the end of sleep, or simply a moment to survey the environment and readjust body position before falling back asleep. Sleepers typically awaken soon after the end of a REM phase or sometimes in the middle of REM. Internal circadian indicators , along with a successful reduction of homeostatic sleep need, typically bring about awakening and
11832-490: The restrictions via exceptions. Prayer and folk magic were more common by night. Amulets 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 alcohol
11948-435: The role of β-alanine as a neurotransmitter that promotes sleep in mice. Familial natural short sleep is a rare, genetic, typically inherited trait where an individual sleeps for fewer hours than average without suffering from daytime sleepiness or other consequences of sleep deprivation . This process is entirely natural in this kind of individual, and it is caused by certain genetic mutations. A person with this trait
12064-400: The rules for that language. Infants who slept within four hours of learning the language could remember the language rules better, while infants who stayed awake longer did not recall those rules as well. There is also a relationship between infants' vocabulary and sleeping: infants who sleep longer at night at 12 months have better vocabularies at 26 months. Children can greatly benefit from
12180-422: The rushing swiftness of a roaring elevated train sat numb. It was as if all the bogies and goblins that had beset her unloved, unloving, and unhappy childhood had come to life with tenfold power to hurt and frighten. Directly filming at night is rarely done. Film stocks and video cameras are much less sensitive to low light environments than the human eye. During the silent film era, night scenes were filmed during
12296-471: The screens of electronic devices such as smartphones and televisions, which emit large amounts of blue light, a form of light typically associated with daytime. This disrupts the release of the hormone melatonin needed to regulate the sleep cycle . The most pronounced physiological changes in sleep occur in the brain. The brain uses significantly less energy during sleep than it does when awake, especially during non-REM sleep. In areas with reduced activity,
12412-405: The sky after sunset and into twilight. There are multiple ways to define twilight, the gradual transition to and from darkness when the Sun is below the horizon. "Civil" twilight occurs when the Sun is between 0 and 6 degrees 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 degrees below
12528-400: The suprachiasmatic nucleus has a direct neural connection to the pineal gland , which releases the hormone melatonin at night. Cortisol levels typically rise throughout the night, peak in the awakening hours , and diminish during the day. Circadian prolactin secretion begins in the late afternoon, especially in women, and is subsequently augmented by sleep-induced secretion, to peak in
12644-561: The table below. Sleep may facilitate the synthesis of molecules that help repair and protect the brain from metabolic end products generated during waking. Anabolic hormones, such as growth hormones , are secreted preferentially during sleep. The brain concentration of glycogen increases during sleep, and is depleted through metabolism during wakefulness. The human organism physically restores itself during sleep, occurring mostly during slow-wave sleep during which body temperature, heart rate, and brain oxygen consumption decrease. In both
12760-444: 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 3 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 6 minutes. Scattered, diffuse sunlight remains in
12876-421: The trough of the cycle. A healthy young adult entrained to the sun will (during most of the year) fall asleep a few hours after sunset, experience body temperature minimum at 6 a.m., and wake up a few hours after sunrise. Generally speaking, the longer an organism is awake, the more it feels a need to sleep ("sleep debt"). This driver of sleep is referred to as Process S . The balance between sleeping and waking
12992-462: 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
13108-631: The work of demons. The idea of night as a dangerous, dark, or haunted time persists in modern urban legends like the vanishing hitchhiker . Many times in the night season, there have been certain spirits heard softly going or spitting or groaning, who being asked what they were have made answer that they were the souls of this or that man and that they now endure extreme torments. In folklore, nocturnal preternatural beings like goblins , fairies , werewolves , pucks , brownies , banshees , and boggarts have overlapping but non-synonymous definitions. The werewolf —and its francophone variations
13224-440: The year. The 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 polar circles , 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
13340-532: Was forbidden for Muslims , after dark, Turkish Muslims went to the 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 , extramarital , 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
13456-486: 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. Nightlife , sometimes referred to as "the night-time economy", is a range of entertainment available and generally more popular from
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