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Night (also described as night time, unconventionally spelled as "nite") is the period of
ambient Ambient or Ambiance or Ambience may refer to: Music and sound * Ambience (sound recording), also known as atmospheres or backgrounds * Ambient music, a genre of music that puts an emphasis on tone and atmosphere * ''Ambient'' (album), by Moby * ...
darkness from
sunset Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth (except the North and South poles), the equinox Sun sets due west at the moment of both the spring ...
to
sunrise Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning. The term can also refer to the entire process of the solar disk crossing the horizon and its accompanying atmospheric effects. Terminology ...
during each 24-hour day, when the Sun is below the horizon. The exact
time Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, t ...
when night begins and ends depends on the location and varies throughout the year, based on factors such as season and
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north po ...
. The word can be used in a different sense as the time between bedtime and morning. In common communication, the word ''night'' is used as a farewell ("good night", sometimes shortened to "night"), mainly when someone is going to sleep or leaving. Astronomical night is the period between astronomical dusk and astronomical
dawn Dawn is the time that marks the beginning of twilight before sunrise. It is recognized by the appearance of indirect sunlight being scattered in Earth's atmosphere, when the centre of the Sun's disc has reached 18° below the observer's ho ...
when the Sun is between 18 and 90 degrees below the horizon and does not illuminate the sky. As seen from
latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north po ...
s between about 48.56° and 65.73° north or south of the
Equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can al ...
, complete darkness does not occur around the summer solstice because, although the Sun sets, it is never more than 18° below the horizon at lower culmination, −90° Sun angles occur at the
Tropic of Cancer The Tropic of Cancer, which is also referred to as the Northern Tropic, is the most northerly circle of latitude on Earth at which the Sun can be directly overhead. This occurs on the June solstice, when the Northern Hemisphere is tilted tow ...
on the December solstice and Tropic of Capricorn on the
June solstice The June solstice is the solstice on Earth that occurs annually between 20 and 22 June according to the Gregorian calendar The Gregorian calendar is the calendar used in most parts of the world. It was introduced in October 1582 by Pop ...
, and at the
equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can al ...
on equinoxes. And as seen from latitudes greater than 72° north or south of the equator, complete darkness does not occur both equinoxes because, although the Sun sets, it is never more than 18° below the horizon. The opposite of night is
day A day is the time period of a full rotation of the Earth with respect to the Sun. On average, this is 24 hours, 1440 minutes, or 86,400 seconds. In everyday life, the word "day" often refers to a solar day, which is the length between two so ...
(or "
daytime Daytime as observed on Earth is the period of the day during which a given location experiences natural illumination from direct sunlight. Daytime occurs when the Sun appears above the local horizon, that is, anywhere on the globe's he ...
", to distinguish it from "day" referring to a 24-hour period). Twilight is the period of night after sunset or before sunrise when the Sun still illuminates the sky when it is below the horizon. At any given time, one side of
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...
is bathed in sunlight (the daytime), while the other side is in
darkness Darkness, the direct opposite of lightness, is defined as a lack of illumination, an absence of visible light, or a surface that absorbs light, such as black or brown. Human vision is unable to distinguish colors in conditions of very low ...
caused by Earth blocking the sunlight. The central part of the shadow is called the umbra, where the night is darkest. Natural illumination at night is still provided by a combination of moonlight, planetary light, starlight, zodiacal light, gegenschein, and airglow. In some circumstances, aurorae,
lightning Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an average ...
, and bioluminescence can provide some illumination. The glow provided by artificial lighting is sometimes referred to as light pollution because it can interfere with observational astronomy and
ecosystem An ecosystem (or ecological system) consists of all the organisms and the physical environment with which they interact. These biotic and abiotic components are linked together through nutrient cycles and energy flows. Energy enters the syst ...
s.


Duration and geography

On Earth, an average night is shorter than
daytime Daytime as observed on Earth is the period of the day during which a given location experiences natural illumination from direct sunlight. Daytime occurs when the Sun appears above the local horizon, that is, anywhere on the globe's he ...
due to two factors. Firstly, the Sun's apparent disk is not a point, but has an angular diameter of about 32
arcminute A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
s (32'). Secondly, the atmosphere refracts sunlight so that some of it reaches the ground when the Sun is below the horizon by about 34'. The combination of these two factors means that light reaches the ground when the center of the solar disk is below the horizon by about 50'. Without these effects, daytime and night would be the same length on both
equinox A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears zenith, directly above the equator, rather than north or south of the equator. On the day of the equinox, the Sun appears to rise "due east" ...
es, the moments when the Sun appears to contact the celestial equator. On the equinoxes, daytime actually lasts almost 14 minutes longer than night does at the
Equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can al ...
, and even longer towards the poles. The
summer Summer is the hottest of the four temperate seasons, occurring after spring and before autumn. At or centred on the summer solstice, the earliest sunrise and latest sunset occurs, daylight hours are longest and dark hours are shortest, ...
and
winter Winter is the coldest season of the year in Polar regions of Earth, polar and temperate climates. It occurs after autumn and before spring (season), spring. The tilt of Axial tilt#Earth, Earth's axis causes seasons; winter occurs when a Hemi ...
solstice A solstice is an event that occurs when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21. In many count ...
s mark the shortest and longest nights, respectively. The closer a location is to either the
North Pole The North Pole, also known as the Geographic North Pole or Terrestrial North Pole, is the point in the Northern Hemisphere where the Earth's rotation, Earth's axis of rotation meets its surface. It is called the True North Pole to distingu ...
or the
South Pole The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on Earth and lies antipod ...
, the wider the range of variation in the night's duration. Although daytime and night nearly equalize in length on the equinoxes, the ratio of night to day changes more rapidly at high latitudes than at low latitudes before and after an equinox. In the Northern Hemisphere,
Denmark ) , song = ( en, "King Christian stood by the lofty mast") , song_type = National and royal anthem , image_map = EU-Denmark.svg , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of Denmark , establishe ...
experiences shorter nights in June than
India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...
. In the Southern Hemisphere,
Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest co ...
sees longer nights in June than
Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the eas ...
. Both hemispheres experience the same patterns of night length at the same latitudes, but the cycles are 6 months apart so that one hemisphere experiences long nights (
winter Winter is the coldest season of the year in Polar regions of Earth, polar and temperate climates. It occurs after autumn and before spring (season), spring. The tilt of Axial tilt#Earth, Earth's axis causes seasons; winter occurs when a Hemi ...
) while the other is experiencing short nights (
summer Summer is the hottest of the four temperate seasons, occurring after spring and before autumn. At or centred on the summer solstice, the earliest sunrise and latest sunset occurs, daylight hours are longest and dark hours are shortest, ...
). In the region within either
polar circle A polar circle is a geographic term for a conditional circular line (arc) referring either to the Arctic Circle or the Antarctic Circle. These are two of the keynote circles of latitude (parallels). On Earth, the Arctic Circle is currently ...
, the variation in daylight hours is so extreme that part of summer sees a period without night intervening between consecutive days, while part of winter sees a period without daytime intervening between consecutive nights.


On other celestial bodies

The phenomenon of day and night is due to the rotation of a celestial body about its axis, creating an illusion of the sun rising and setting. Different bodies spin at very different rates, however. Some may spin much faster than
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...
, while others spin extremely slowly, leading to very long days and nights. The planet
Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never f ...
rotates once every 224.7 days – by far the slowest rotation period of any of the major planets. In contrast, the gas giant
Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandt ...
's sidereal day is only 9 hours and 56 minutes. However, it is not just the sidereal rotation period which determines the length of a planet's day-night cycle but the length of its orbital period as well - Venus has a rotation period of 224.7 days, but a day-night cycle just 116.75 days long due to its retrograde rotation and orbital motion around the Sun. Mercury has the longest day-night cycle as a result of its 3:2 resonance between its orbital period and rotation period - this resonance gives it a day-night cycle that is 176 days long. A planet may experience large temperature variations between day and night, such as Mercury, the planet closest to the sun. This is one consideration in terms of planetary habitability or the possibility of extraterrestrial life.


Effect on life


Biological

The disappearance of sunlight, the primary
energy In physics, energy (from Ancient Greek: ἐνέργεια, ''enérgeia'', “activity”) is the quantitative property that is transferred to a body or to a physical system, recognizable in the performance of work and in the form of hea ...
source for
life Life is a quality that distinguishes matter that has biological processes, such as Cell signaling, signaling and self-sustaining processes, from that which does not, and is defined by the capacity for Cell growth, growth, reaction to Stimu ...
on Earth, has dramatic effects on the morphology,
physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemic ...
and behavior of almost every organism. Some animals
sleep Sleep is a sedentary state of mind and body. It is characterized by altered consciousness, relatively inhibited Perception, sensory activity, reduced muscle activity and reduced interactions with surroundings. It is distinguished from wakefuln ...
during the night, while other nocturnal animals, including
moth Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of ...
s and
cricket Cricket is a bat-and-ball game played between two teams of eleven players on a field at the centre of which is a pitch with a wicket at each end, each comprising two bails balanced on three stumps. The batting side scores runs by st ...
s, are active during this time. The effects of day and night are not seen in the animal kingdom alone
plant Plants are predominantly Photosynthesis, photosynthetic eukaryotes of the Kingdom (biology), kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all curr ...
s have also evolved adaptations to cope best with the lack of sunlight during this time. For example, crassulacean acid metabolism is a unique type of carbon fixation which allows some photosynthetic plants to store
carbon dioxide Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
in their tissues as organic acids during the night, which can then be used during the day to synthesize
carbohydrate In organic chemistry, a carbohydrate () is a biomolecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) and thus with the empirical formula (where ''m'' may or ...
s. This allows them to keep their stomata closed during the daytime, preventing transpiration of
water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...
when it is precious.


Social

The first constant electric light was demonstrated in 1835. As artificial
lighting Lighting or illumination is the deliberate use of light to achieve practical or aesthetic effects. Lighting includes the use of both artificial light sources like lamps and light fixtures, as well as natural illumination by capturing dayli ...
has improved, especially after the
Industrial Revolution The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...
, night time activity has increased and become a significant part of the
economy An economy is an area of the production, distribution and trade, as well as consumption of goods and services. In general, it is defined as a social domain that emphasize the practices, discourses, and material expressions associated with t ...
in most places. Many establishments, such as nightclubs, bars, convenience stores, fast-food restaurants, gas stations, distribution facilities, and
police station A police station (sometimes called a "station house" or just "house") is a building which serves to accommodate police officers and other members of staff. These buildings often contain offices and accommodation for personnel and vehicles, al ...
s now operate 24 hours a day or stay open as late as 1 or 2 a.m. Even without artificial light, moonlight sometimes makes it possible to travel or work outdoors at night. Nightlife is a collective term for
entertainment Entertainment is a form of activity that holds the attention and interest of an audience or gives pleasure and delight. It can be an idea or a task, but is more likely to be one of the activities or events that have developed over thousan ...
that is available and generally more popular from the late evening into the early hours of the morning. It includes pubs, bars, nightclubs, parties, live
music Music is generally defined as the The arts, art of arranging sound to create some combination of Musical form, form, harmony, melody, rhythm or otherwise Musical expression, expressive content. Exact definition of music, definitions of mu ...
,
concert A concert is a live music performance in front of an audience. The performance may be by a single musician, sometimes then called a recital, or by a musical ensemble, such as an orchestra, choir, or band. Concerts are held in a wide variet ...
s,
cabaret Cabaret is a form of theatrical entertainment featuring music, song, dance, recitation, or drama. The performance venue might be a pub, a casino, a hotel, a restaurant, or a nightclub with a stage for performances. The audience, often dinin ...
s,
theatre Theatre or theater is a collaborative form of performing art that uses live performers, usually actors or actresses, to present the experience of a real or imagined event before a live audience in a specific place, often a stage. The perfor ...
, cinemas, and shows. These venues often require a cover charge for admission. Nightlife entertainment is often more
adult An adult is a human or other animal that has reached full growth. In human context, the term ''adult'' has meanings associated with social and legal concepts. In contrast to a "minor", a legal adult is a person who has attained the age of ...
-oriented than daytime entertainment.


Cultural and psychological aspects

Night is often associated with danger and evil, because of the psychological connection of night's all-encompassing darkness to the
fear Fear is an intensely unpleasant emotion in response to perceiving or recognizing a danger or threat. Fear causes physiological changes that may produce behavioral reactions such as mounting an aggressive response or fleeing the threat. Fear ...
of the unknown and darkness's hindrance of a major sensory system (the sense of
sight Visual perception is the ability to interpret the surrounding environment through photopic vision (daytime vision), color vision, scotopic vision (night vision), and mesopic vision (twilight vision), using light in the visible spectrum refl ...
). Nighttime is naturally associated with vulnerability and danger for human physical survival. Criminals, animals, and other potential dangers can be concealed by darkness.
Midnight Midnight is the transition time from one day to the next – the moment when the date changes, on the local official clock time for any particular jurisdiction. By clock time, midnight is the opposite of noon, differing from it by 12 hours ...
has a particular importance in human imagination and culture. Upper Paleolithic art was found to show (by Leroi-Gourhan) a pattern of choices where the portrayal of animals that were experienced as dangerous were located at a distance from the entrance of a cave dwelling at a number of different cave locations. The belief in magic often includes the idea that magic and magicians are more powerful at night. Séances of spiritualism are usually conducted closer to midnight. Similarly, mythical and folkloric creatures such as vampires and werewolves are described as being more active at night.
Ghost A ghost is the soul (spirit), soul or spirit of a dead Human, person or animal that is believed to be able to appear to the living. In ghostlore, descriptions of ghosts vary widely from an invisible presence to translucent or barely visibl ...
s are believed to wander around almost exclusively during night-time. In almost all cultures, there exist stories and legends warning of the dangers of night-time. In fact, the Saxons called the darkness of night the "death mist". The cultural significance of the night in Islam differs from that in Western culture. The
Quran The Quran (, ; Standard Arabic: , Quranic Arabic: , , 'the recitation'), also romanized Qur'an or Koran, is the central religious text of Islam, believed by Muslims to be a revelation from God. It is organized in 114 chapters (pl.: , sing.: ...
was revealed during the Night of Power, the most significant night according to Islam.
Muhammad Muhammad ( ar, مُحَمَّد;  570 – 8 June 632 CE) was an Arab religious, social, and political leader and the founder of Islam. According to Islamic doctrine, he was a prophet divinely inspired to preach and confirm the monot ...
made his famous journey from Mecca to Jerusalem and then to heaven in the night. Another prophet,
Abraham Abraham, ; ar, , , name=, group= (originally Abram) is the common Hebrews, Hebrew patriarch of the Abrahamic religions, including Judaism, Christianity, and Islam. In Judaism, he is the founding father of the Covenant (biblical), special ...
came to a realization of the supreme being in charge of the universe at night. People who prefer to be active during the night-time are called night owls.


See also

* Earth's shadow * Night aviation regulations in the US * Night sky *
Nocturne A nocturne is a musical composition that is inspired by, or evocative of, the night. History The term ''nocturne'' (from French '' nocturne'' 'of the night') was first applied to musical pieces in the 18th century, when it indicated an ensemb ...
* Olbers' paradox


References


Further reading


Culture

* *


External links

* * {{Authority control Darkness Night Parts of a day Time in astronomy