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An hour (
symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...
: h; also abbreviated hr) is a unit of
time Time is the continued sequence of existence and event (philosophy), events that occurs in an apparently irreversible process, irreversible succession from the past, through the present, into the future. It is a component quantity of various me ...
conventionally reckoned as of a day and scientifically reckoned between 3,599 and 3,601 seconds, depending on the speed of Earth's rotation. There are 60 minutes in an hour, and 24 hours in a day. The hour was initially established in the
ancient Near East The ancient Near East was the home of early civilizations within a region roughly corresponding to the modern Middle East: Mesopotamia (modern Iraq, southeast Turkey, southwest Iran and northeastern Syria), ancient Egypt, ancient Iran ( Elam, ...
as a variable measure of of the
night Night (also described as night time, unconventionally spelled as "nite") is the period of ambient darkness from sunset to sunrise during each 24-hour day, when the Sun is below the horizon. The exact time when night begins and ends depends ...
or daytime. Such seasonal, temporal, or unequal hours varied by
season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and ...
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 ...
. Equal or equinoctial hours were taken as of the day as measured from noon to noon; the minor seasonal variations of this unit were eventually smoothed by making it of the mean solar day. Since this unit was not constant due to long term variations in the Earth's rotation, the hour was finally separated from the Earth's rotation and defined in terms of the atomic or physical second. In the modern
metric system The metric system is a system of measurement that succeeded the decimalised system based on the metre that had been introduced in France in the 1790s. The historical development of these systems culminated in the definition of the Intern ...
, hours are an accepted unit of time defined as 3,600 atomic seconds. However, on rare occasions an hour may incorporate a positive or negative
leap second A leap second is a one- second adjustment that is occasionally applied to Coordinated Universal Time (UTC), to accommodate the difference between precise time ( International Atomic Time (TAI), as measured by atomic clocks) and imprecise obser ...
, making it last 3,599 or 3,601 seconds, in order to keep it within 0.9 seconds of UT1, which is based on measurements of the mean solar day.


Name

''Hour'' is a development of the
Anglo-Norman Anglo-Norman may refer to: *Anglo-Normans, the medieval ruling class in England following the Norman conquest of 1066 *Anglo-Norman language **Anglo-Norman literature *Anglo-Norman England, or Norman England, the period in English history from 1066 ...
' and
Middle English Middle English (abbreviated to ME) is a form of the English language that was spoken after the Norman conquest of 1066, until the late 15th century. The English language underwent distinct variations and developments following the Old Englis ...
', first attested in the 13th century. It displaced tide tīd, "time" and stound stund, ''span of time''. The Anglo-Norman term was a borrowing of
Old French Old French (, , ; Modern French: ) was the language spoken in most of the northern half of France from approximately the 8th to the 14th centuries. Rather than a unified language, Old French was a linkage of Romance dialects, mutually intel ...
', a variant of ', which derived from
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
' and Greek ''hṓrā'' (). Like Old English ' and ', ''hṓrā'' was originally a vaguer word for any span of time, including
season A season is a division of the year based on changes in weather, ecology, and the number of daylight hours in a given region. On Earth, seasons are the result of the axial parallelism of Earth's tilted orbit around the Sun. In temperate and ...
s and
year A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the h ...
s. Its
Proto-Indo-European Proto-Indo-European (PIE) is the reconstructed common ancestor of the Indo-European language family. Its proposed features have been derived by linguistic reconstruction from documented Indo-European languages. No direct record of Proto-Indo ...
root In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the su ...
has been reconstructed as ' ("year, summer"), making ''hour'' distantly
cognate In historical linguistics, cognates or lexical cognates are sets of words in different languages that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical ef ...
with ''
year A year or annus is the orbital period of a planetary body, for example, the Earth, moving in its orbit around the Sun. Due to the Earth's axial tilt, the course of a year sees the passing of the seasons, marked by change in weather, the h ...
''. The time of day is typically expressed in English in terms of hours. Whole hours on a 12-hour clock are expressed using the contracted phrase ''o'clock'', from the older ''of the clock''. (10 am and 10 pm are both read as "ten o'clock".) Hours on a 24-hour clock ("military time") are expressed as "hundred" or "hundred hours". (1000 is read "ten hundred" or "ten hundred hours"; 10 pm would be "twenty-two hundred".) Fifteen and thirty minutes past the hour is expressed as "a quarter past" or "after" and "half past", respectively, from their fraction of the hour. Fifteen minutes before the hour may be expressed as "a quarter to", "of", "till", or "before" the hour. (9:45 may be read "nine forty-five" or "a quarter till ten".)


History


Antiquity

The ancient Greeks kept time differently from the way we do today. Instead of dividing the time between one midnight and the next into 24 equal hours, they divided the time from sunrise to sunset into 12 "seasonal hours" (their actual duration depending on season), and the time from sunset to the next sunrise again in 12 "seasonal hours". Initially, only the day was divided into 12 seasonal hours and the night into 3 or 4 night watches. By the
Hellenistic period In Classical antiquity, the Hellenistic period covers the time in Mediterranean history after Classical Greece, between the death of Alexander the Great in 323 BC and the emergence of the Roman Empire, as signified by the Battle of Actium in ...
the night was also divided into 12 hours. The day-and-night () was probably first divided into twenty-four hours by Hipparchus of Nicaea. The Greek astronomer Andronicus of Cyrrhus oversaw the construction of a
horologion The ''Horologion'' ( grc-gre, Ὡρολόγιον; Church Slavonic: Часocлoвъ, ''Chasoslov'', ro, Ceaslov) or '' Book of hours'' provides the fixed portions (Greek: , ''akolouthiai'') of the Divine Service or the daily cycle of services ...
called the Tower of the Winds in Athens during the first century BCE. This structure tracked a 24-hour day using both sundials and mechanical hour indicators. The canonical hours were introduced to
early Christianity Early Christianity (up to the First Council of Nicaea in 325) spread from the Levant, across the Roman Empire, and beyond. Originally, this progression was closely connected to already established Jewish centers in the Holy Land and the Jewis ...
from
Second Temple Judaism Second Temple Judaism refers to the Jewish religion as it developed during the Second Temple period, which began with the construction of the Second Temple around 516 BCE and ended with the Roman siege of Jerusalem in 70 CE. The Second Temple ...
. By AD 60, the '' Didache'' recommends disciples to pray the
Lord's Prayer The Lord's Prayer, also called the Our Father or Pater Noster, is a central Christian prayer which Jesus taught as the way to pray. Two versions of this prayer are recorded in the gospels: a longer form within the Sermon on the Mount in the Gosp ...
three times a day; this practice found its way into the canonical hours as well. By the second and third centuries, such
Church Fathers The Church Fathers, Early Church Fathers, Christian Fathers, or Fathers of the Church were ancient and influential Christian theologians and writers who established the intellectual and doctrinal foundations of Christianity. The historical per ...
as
Clement of Alexandria Titus Flavius Clemens, also known as Clement of Alexandria ( grc , Κλήμης ὁ Ἀλεξανδρεύς; – ), was a Christian theologian and philosopher who taught at the Catechetical School of Alexandria. Among his pupils were Origen ...
,
Origen Origen of Alexandria, ''Ōrigénēs''; Origen's Greek name ''Ōrigénēs'' () probably means "child of Horus" (from , "Horus", and , "born"). ( 185 – 253), also known as Origen Adamantius, was an early Christian scholar, ascetic, and the ...
, and
Tertullian Tertullian (; la, Quintus Septimius Florens Tertullianus; 155 AD – 220 AD) was a prolific early Christian author from Carthage in the Roman province of Africa. He was the first Christian author to produce an extensive corpus of L ...
wrote of the practice of Morning and Evening Prayer, and of the prayers at the third, sixth and ninth hours. In the early church, during the night before every feast, a vigil was kept. The word "Vigils", at first applied to the Night Office, comes from a Latin source, namely the ''Vigiliae'' or nocturnal watches or guards of the soldiers. The night from six o'clock in the evening to six o'clock in the morning was divided into four watches or vigils of three hours each, the first, the second, the third, and the fourth vigil. The '' Horae'' were originally personifications of seasonal aspects of nature, not of the time of day. The list of twelve ''Horae'' representing the twelve hours of the day is recorded only in
Late Antiquity Late antiquity is the time of transition from classical antiquity to the Middle Ages, generally spanning the 3rd–7th century in Europe and adjacent areas bordering the Mediterranean Basin. The popularization of this periodization in English h ...
, by Nonnus. The first and twelfth of the ''Horae'' were added to the original set of ten: # ''Auge'' (first light) # ''Anatole'' (sunrise)] # ''Mousike'' (morning hour of music and study) # ''Gymnastike'' (morning hour of exercise) # ''Nymphe'' (morning hour of ablutions) # ''Mesembria'' (noon) # ''Sponde'' (libations poured after lunch) # ''Elete'' (prayer) # ''Akte'' (eating and pleasure) # ''Hesperis'' (start of evening) # ''Dysis'' (sunset) # ''Arktos'' (night sky)


Middle Ages

Medieval astronomers such as al-Biruni and Sacrobosco, divided the hour into 60 minutes, each of 60 seconds; this derives from
Babylonian astronomy Babylonian astronomy was the study or recording of celestial objects during the early history of Mesopotamia. Babylonian astronomy seemed to have focused on a select group of stars and constellations known as Ziqpu stars. These constellation ...
, where the corresponding terms denoted the time required for the Sun's apparent motion through the ecliptic to describe one minute or second of arc, respectively. In present terms, the Babylonian degree of time was thus four minutes long, the "minute" of time was thus four seconds long and the "second" 1/15 of a second.) In medieval Europe, the Roman hours continued to be marked on
sundial A sundial is a horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a f ...
s but the more important units of time were the canonical hours of the Orthodox and
Catholic Church The Catholic Church, also known as the Roman Catholic Church, is the List of Christian denominations by number of members, largest Christian church, with 1.3 billion baptized Catholics Catholic Church by country, worldwide . It is am ...
. During daylight, these followed the pattern set by the three-hour bells of the Roman markets, which were succeeded by the
bells Bells may refer to: * Bell, a musical instrument Places * Bells, North Carolina * Bells, Tennessee * Bells, Texas * Bells Beach, Victoria, an internationally famous surf beach in Australia * Bells Corners, Ontario Music * Bells, directly st ...
of local churches. They rang
prime A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways ...
at about 6am,
terce Terce is a canonical hour of the Divine Office. It consists mainly of psalms and is held around 9 a.m. Its name comes from Latin and refers to the third hour of the day after dawn. With Sext, None and Compline it belongs to the so-called "Litt ...
at about 9am, sext at noon, nones at about 3pm, and
vespers Vespers is a service of evening prayer, one of the canonical hours in Eastern Orthodox, Oriental Orthodox, Catholic (both Latin and Eastern), Lutheran, and Anglican liturgies. The word for this fixed prayer time comes from the Latin , mea ...
at either 6pm or sunset.
Matins Matins (also Mattins) is a canonical hour in Christian liturgy, originally sung during the darkness of early morning. The earliest use of the term was in reference to the canonical hour, also called the vigil, which was originally celebrated ...
and lauds precede these irregularly in the morning hours; compline follows them irregularly before sleep; and the midnight office follows that. Vatican II ordered their reformation for the Catholic Church in 1963, though they continue to be observed in the Orthodox churches. When mechanical
clock A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and ...
s began to be used to show hours of daylight or nighttime, their period needed to be changed every morning and evening (for example, by changing the length of their pendula). The use of 24 hours for the entire day meant hours varied much less and the clocks needed to be adjusted only a few times a month.


Modernity

The minor irregularities of the apparent solar day were smoothed by measuring time using the mean solar day, using the Sun's movement along the celestial equator rather than along the ecliptic. The irregularities of this time system were so minor that most clocks reckoning such hours did not need adjustment. However, scientific measurements eventually became precise enough to note the effect of tidal deceleration of the
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 sur ...
by the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, which gradually lengthens the Earth's days. During the
French Revolution The French Revolution ( ) was a period of radical political and societal change in France that began with the Estates General of 1789 and ended with the formation of the French Consulate in November 1799. Many of its ideas are conside ...
, a general decimalisation of measures was enacted, including decimal time between 1793 and 1795. Under its provisions, the French hour (french: ) was of the day and divided formally into 100 decimal minutes (') and informally into 10 tenths ('). This hour was only briefly in official use, being repealed by the same 1795 legislation that first established the metric system. The
metric system The metric system is a system of measurement that succeeded the decimalised system based on the metre that had been introduced in France in the 1790s. The historical development of these systems culminated in the definition of the Intern ...
bases its measurements of time upon the second, defined since 1952 in terms of the Earth's rotation in AD1900. Its hours are a secondary unit computed as precisely 3,600 seconds. However, an hour of
Coordinated Universal Time Coordinated Universal Time or UTC is the primary time standard by which the world regulates clocks and time. It is within about one second of Solar time#Mean solar time, mean solar time (such as Universal Time, UT1) at 0° longitude (at the I ...
(UTC), used as the basis of most civil time, has lasted 3,601 seconds 27 times since 1972 in order to keep it within 0.9 seconds of
universal time Universal Time (UT or UT1) is a time standard based on Earth's rotation. While originally it was mean solar time at 0° longitude, precise measurements of the Sun are difficult. Therefore, UT1 is computed from a measure of the Earth's angle wit ...
, which is based on measurements of the mean solar day at 0° longitude. The addition of these seconds accommodates the very gradual slowing of the rotation of the
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 sur ...
. In modern life, the ubiquity of clocks and other timekeeping devices means that segmentation of days according to their hours is commonplace. Most forms of
employment Employment is a relationship between two parties regulating the provision of paid labour services. Usually based on a contract, one party, the employer, which might be a corporation, a not-for-profit organization, a co-operative, or any o ...
, whether wage or
salaried A salary is a form of periodic payment from an employer to an employee, which may be specified in an employment contract. It is contrasted with piece wages, where each job, hour or other unit is paid separately, rather than on a periodic basis. F ...
labour, involve compensation based upon measured or expected hours worked. The fight for an eight-hour day was a part of
labour movement The labour movement or labor movement consists of two main wings: the trade union movement (British English) or labor union movement (American English) on the one hand, and the political labour movement on the other. * The trade union movement ...
s around the world. Informal rush hours and happy hours cover the times of day when commuting slows down due to congestion or alcoholic drinks being available at discounted prices. The hour record for the greatest distance travelled by a cyclist within the span of an hour is one of
cycling Cycling, also, when on a two-wheeled bicycle, called bicycling or biking, is the use of cycles for transport, recreation, exercise or sport. People engaged in cycling are referred to as "cyclists", "bicyclists", or "bikers". Apart from ...
's greatest honours.


Counting hours

Many different ways of counting the hours have been used. Because sunrise, sunset, and, to a lesser extent, noon, are the conspicuous points in the day, starting to count at these times was, for most people in most early societies, much easier than starting at midnight. However, with accurate clocks and modern astronomical equipment (and the telegraph or similar means to transfer a time signal in a split-second), this issue is much less relevant. Astrolabes,
sundial A sundial is a horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a f ...
s, and astronomical clocks sometimes show the hour length and count using some of these older definitions and counting methods.


Counting from dawn

In ancient and medieval cultures, the counting of hours generally started with sunrise. Before the widespread use of artificial light, societies were more concerned with the division between night and day, and daily routines often began when light was sufficient. "Babylonian hours" divide the day and night into 24 equal hours, reckoned from the time of sunrise. They are so named from the false belief of ancient authors that the Babylonians divided the day into 24 parts, beginning at sunrise. In fact, they divided the day into 12 parts (called ''kaspu'' or "double hours") or into 60 equal parts.


Unequal hours

Sunrise marked the beginning of the first hour, the middle of the day was at the end of the sixth hour and sunset at the end of the twelfth hour. This meant that the duration of hours varied with the season. In the Northern hemisphere, particularly in the more northerly latitudes, summer daytime hours were longer than winter daytime hours, each being one twelfth of the time between sunrise and sunset. These variable-length hours were variously known as temporal, unequal, or seasonal hours and were in use until the appearance of the mechanical clock, which furthered the adoption of equal length hours. This is also the system used in
Jewish law ''Halakha'' (; he, הֲלָכָה, ), also transliterated as ''halacha'', ''halakhah'', and ''halocho'' ( ), is the collective body of Jewish religious laws which is derived from the written and Oral Torah. Halakha is based on biblical comman ...
and frequently called " Talmudic hour" (''Sha'a Zemanit'') in a variety of texts. The Talmudic hour is one twelfth of time elapsed from sunrise to sunset, day hours therefore being longer than night hours in the summer; in winter they reverse. The Indic day began at sunrise. The term ''hora'' was used to indicate an hour. The time was measured based on the length of the shadow at day time. A ''hora'' translated to 2.5 ''pe''. There are 60 ''pe'' per day, 60 minutes per ''pe'' and 60 ''kshana'' (snap of a finger or instant) per minute. ''Pe'' was measured with a bowl with a hole placed in still water. Time taken for this graduated bowl was one ''pe''. Kings usually had an officer in charge of this clock.


Counting from sunset

In so-called " Italian time", "Italian hours", or "old Czech time", the first hour started with the sunset
Angelus The Angelus (; Latin for "angel") is a Catholic devotion commemorating the Incarnation of Christ. As with many Catholic prayers, the name ''Angelus'' is derived from its incipit—the first few words of the text: ("The Angel of the Lord ...
bell (or at the end of dusk, i.e., half an hour after sunset, depending on local custom and geographical latitude). The hours were numbered from 1 to 24. For example, in Lugano, the sun rose in December during the 14th hour and noon was during the 19th hour; in June the sun rose during the 7th hour and noon was in the 15th hour. Sunset was always at the end of the 24th hour. The clocks in church towers struck only from 1 to 12, thus only during night or early morning hours. This manner of counting hours had the advantage that everyone could easily know how much time they had to finish their day's work without artificial light. It was already widely used in
Italy Italy ( it, Italia ), officially the Italian Republic, ) or the Republic of Italy, is a country in Southern Europe. It is located in the middle of the Mediterranean Sea, and its territory largely coincides with the homonymous geographical ...
by the 14th century and lasted until the mid-18th century; it was officially abolished in 1755, or in some regions customary until the mid-19th century. The system of Italian hours can be seen on a number of clocks in Europe, where the dial is numbered from 1 to 24 in either Roman or Arabic numerals. The
St Mark's Clock St Mark's Clock is housed in the Clock Tower on the Piazza San Marco (Saint Mark's Square) in Venice, Italy, adjoining the Procuratie Vecchie. The first clock housed in the tower was built and installed by Gian Paolo and Gian Carlo Rainieri, fa ...
in Venice, and the Orloj in Prague are famous examples. It was also used in
Poland Poland, officially the Republic of Poland, is a country in Central Europe. It is divided into 16 administrative provinces called voivodeships, covering an area of . Poland has a population of over 38 million and is the fifth-most populou ...
and
Bohemia Bohemia ( ; cs, Čechy ; ; hsb, Čěska; szl, Czechy) is the westernmost and largest historical region of the Czech Republic. Bohemia can also refer to a wider area consisting of the historical Lands of the Bohemian Crown ruled by the Bohem ...
until the 17th century. The
Islamic Islam (; ar, ۘالِإسلَام, , ) is an Abrahamic monotheistic religion centred primarily around the Quran, a religious text considered by Muslims to be the direct word of God (or '' Allah'') as it was revealed to Muhammad, the ma ...
day begins at sunset. The first prayer of the day ( maghrib) is to be performed between just after sunset and the end of twilight. Until 1968 Saudi Arabia used the system of counting 24 equal hours with the first hour starting at sunset.


Counting from noon

For many centuries, up to 1925, astronomers counted the hours and days from noon, because it was the easiest solar event to measure accurately. An advantage of this method (used in the Julian Date system, in which a new Julian Day begins at noon) is that the date doesn't change during a single night's observing.


Counting from midnight

In the modern 12-hour clock, counting the hours starts at midnight and restarts at noon. Hours are numbered 12, 1, 2, ..., 11. Solar noon is always close to 12 noon (ignoring artificial adjustments due to time zones and
daylight saving time Daylight saving time (DST), also referred to as daylight savings time or simply daylight time (United States, Canada, and Australia), and summer time (United Kingdom, European Union, and others), is the practice of advancing clocks (typicall ...
), differing according to the equation of time by as much as fifteen minutes either way. At the equinoxes sunrise is around 6 a.m. ( la, ante meridiem, before noon), and sunset around 6 p.m. ( la, post meridiem, after noon). In the modern 24-hour clock, counting the hours starts at midnight, and hours are numbered from 0 to 23. Solar noon is always close to 12:00, again differing according to the equation of time. At the equinoxes sunrise is around 06:00, and sunset around 18:00.


History of timekeeping in other cultures


Egypt

The ancient Egyptians began dividing the night into ' at some time before the compilation of the Dynasty V
Pyramid Texts The Pyramid Texts are the oldest ancient Egyptian funerary texts, dating to the late Old Kingdom. They are the earliest known corpus of ancient Egyptian religious texts. Written in Old Egyptian, the pyramid texts were carved onto the subterran ...
in the 24thcenturyBC. By 2150BC ( Dynasty IX), diagrams of stars inside Egyptian coffin lids—variously known as "diagonal calendars" or "star clocks"—attest that there were exactly 12 of these. Clagett writes that it is "certain" this duodecimal division of the night followed the adoption of the Egyptian civil calendar, usually placed BC on the basis of analyses of the Sothic cycle, but a
lunar calendar A lunar calendar is a calendar based on the monthly cycles of the Moon's phases ( synodic months, lunations), in contrast to solar calendars, whose annual cycles are based only directly on the solar year. The most commonly used calendar, t ...
presumably long predated this and also would have had twelve months in each of its years. The coffin diagrams show that the Egyptians took note of the
heliacal rising The heliacal rising ( ) or star rise of a star occurs annually, or the similar phenomenon of a planet, when it first becomes visible above the eastern horizon at dawn just before sunrise (thus becoming "the morning star") after a complete orbit o ...
s of 36 stars or constellations (now known as " decans"), one for each of the ten-day "weeks" of their civil calendar. (12 sets of alternate "triangle decans" were used for the 5
epagomenal days Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of both days and months. S ...
between years.) Each night, the rising of eleven of these decans were noted, separating the night into twelve divisions whose middle terms would have lasted about 40 minutes each. (Another seven stars were noted by the Egyptians during the twilight and predawn periods, although they were not important for the hour divisions.) The original decans used by the Egyptians would have fallen noticeably out of their proper places over a span of several centuries. By the time of (BC), the priests at
Karnak The Karnak Temple Complex, commonly known as Karnak (, which was originally derived from ar, خورنق ''Khurnaq'' "fortified village"), comprises a vast mix of decayed temples, pylons, chapels, and other buildings near Luxor, Egypt. Constru ...
were using
water clock A water clock or clepsydra (; ; ) is a timepiece by which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel, and where the amount is then measured. Water clocks are one of the oldest time- ...
s to determine the hours. These were filled to the brim at sunset and the hour determined by comparing the water level against one of its twelve gauges, one for each month of the year. During the
New Kingdom New is an adjective referring to something recently made, discovered, or created. New or NEW may refer to: Music * New, singer of K-pop group The Boyz Albums and EPs * ''New'' (album), by Paul McCartney, 2013 * ''New'' (EP), by Regurgitator ...
, another system of decans was used, made up of 24 stars over the course of the year and 12 within any one night. The later division of the day into 12 hours was accomplished by
sundial A sundial is a horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the apparent position of the Sun in the sky. In the narrowest sense of the word, it consists of a f ...
s marked with ten equal divisions. The morning and evening periods when the sundials failed to note time were observed as the first and last hours. The Egyptian hours were closely connected both with the priesthood of the gods and with their divine services. By the
New Kingdom New is an adjective referring to something recently made, discovered, or created. New or NEW may refer to: Music * New, singer of K-pop group The Boyz Albums and EPs * ''New'' (album), by Paul McCartney, 2013 * ''New'' (EP), by Regurgitator ...
, each hour was conceived as a specific region of the sky or
underworld The underworld, also known as the netherworld or hell, is the supernatural world of the dead in various religious traditions and myths, located below the world of the living. Chthonic is the technical adjective for things of the underwo ...
through which Ra's
solar barge Solar barques were the vessels used by the sun god Ra in ancient Egyptian mythology. During the day, Ra was said to use a vessel called the Mandjet ( egy, mꜥnḏt) or the Boat of Millions of Years ( egy, wjꜣ-n-ḥḥw), and the vessel he ...
travelled. Protective deities were assigned to each and were used as the names of the hours. As the protectors and resurrectors of the sun, the goddesses of the night hours were considered to hold power over all lifespans and thus became part of Egyptian funerary rituals. Two fire-spitting cobras were said to guard the gates of each hour of the underworld, and
Wadjet Wadjet (; egy, wꜢḏyt "Green One"), known to the Greek world as Uto (; grc-koi, Οὐτώ) or Buto (; ) among other renderings including Wedjat, Uadjet, and Udjo, was originally the ancient local goddess of the city of Dep. It became part ...
and the rearing cobra (
uraeus The Uraeus (), or Ouraeus (Ancient Greek: , ; Egyptian: ', "rearing cobra"), ''(plural: Uraei)'' is the stylized, upright form of an Egyptian cobra, used as a symbol of sovereignty, royalty, deity and divine authority in ancient Egypt. Symbol ...
) were also sometimes referenced as ' from their role protecting the dead through these gates. The Egyptian word for
astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...
, used as a synonym for priest, was ', "one of the ''wnwt''", as it were "one of the hours". The earliest forms of ' include one or three stars, with the later solar hours including the determinative hieroglyph for "sun".


East Asia

Ancient China The earliest known written records of the history of China date from as early as 1250 BC, from the Shang dynasty (c. 1600–1046 BC), during the reign of king Wu Ding. Ancient historical texts such as the '' Book of Documents'' (early chapt ...
divided its day into 100 "marks" running from midnight to midnight. The system is said to have been used since remote antiquity, credited to the legendary
Yellow Emperor The Yellow Emperor, also known as the Yellow Thearch or by his Chinese name Huangdi (), is a deity ('' shen'') in Chinese religion, one of the legendary Chinese sovereigns and culture heroes included among the mytho-historical Three Soverei ...
, but is first attested in Han-era
water clock A water clock or clepsydra (; ; ) is a timepiece by which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel, and where the amount is then measured. Water clocks are one of the oldest time- ...
s and in the 2nd-century history of that
dynasty A dynasty is a sequence of rulers from the same family,''Oxford English Dictionary'', "dynasty, ''n''." Oxford University Press (Oxford), 1897. usually in the context of a monarchical system, but sometimes also appearing in republics. A ...
. It was measured with sundials and
water clock A water clock or clepsydra (; ; ) is a timepiece by which time is measured by the regulated flow of liquid into (inflow type) or out from (outflow type) a vessel, and where the amount is then measured. Water clocks are one of the oldest time- ...
s. Into the Eastern Han, the Chinese measured their day schematically, adding the 20-''ke'' difference between the solstices evenly throughout the year, one every nine days. During the night, time was more commonly reckoned during the night by the "watches" of the guard, which were reckoned as a fifth of the time from sunset to sunrise. Imperial China continued to use ''ke'' and ''geng'' but also began to divide the day into 12 "double hours" named after the earthly branches and sometimes also known by the name of the corresponding animal of the Chinese zodiac. The first ''shi'' originally ran from 11pm to 1am but was reckoned as starting at midnight by the time of the History of Song, compiled during the early Yuan. These apparently began to be used during the Eastern Han that preceded the
Three Kingdoms The Three Kingdoms () from 220 to 280 AD was the tripartite division of China among the dynastic states of Cao Wei, Shu Han, and Eastern Wu. The Three Kingdoms period was preceded by the Eastern Han dynasty and was followed by the West ...
era, but the sections that would have covered them are missing from their official histories; they first appear in official use in the
Tang Tang or TANG most often refers to: * Tang dynasty * Tang (drink mix) Tang or TANG may also refer to: Chinese states and dynasties * Jin (Chinese state) (11th century – 376 BC), a state during the Spring and Autumn period, called Tang (唐) ...
-era
Book of Sui The ''Book of Sui'' (''Suí Shū'') is the official history of the Sui dynasty. It ranks among the official Twenty-Four Histories of imperial China. It was written by Yan Shigu, Kong Yingda, and Zhangsun Wuji, with Wei Zheng as the lead author. ...
. Variations of all these units were subsequently adopted by
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
and the other countries of the
Sinosphere The East Asian cultural sphere, also known as the Sinosphere, the Sinic world, the Sinitic world, the Chinese cultural sphere, the Chinese character sphere encompasses multiple countries in East Asia and Southeast Asia that were historically ...
. The 12 ''shi'' supposedly began to be divided into 24 hours under the
Tang Tang or TANG most often refers to: * Tang dynasty * Tang (drink mix) Tang or TANG may also refer to: Chinese states and dynasties * Jin (Chinese state) (11th century – 376 BC), a state during the Spring and Autumn period, called Tang (唐) ...
, although they are first attested in the
Ming The Ming dynasty (), officially the Great Ming, was an imperial dynasty of China, ruling from 1368 to 1644 following the collapse of the Mongol-led Yuan dynasty. The Ming dynasty was the last orthodox dynasty of China ruled by the Han pe ...
-era Book of Yuan. In that work, the hours were known by the same earthly branches as the ''shi'', with the first half noted as its "starting" and the second as "completed" or "proper" ''shi''. In modern China, these are instead simply numbered and described as "little ''shi''". The modern ''ke'' is now used to count quarter-hours, rather than a separate unit. As with the Egyptian night and daytime hours, the division of the day into twelve ''shi'' has been credited to the example set by the rough number of lunar cycles in a solar year, although the 12-year Jovian orbital cycle was more important to traditional Chinese and Babylonian reckoning of the zodiac.


Southeast Asia

In
Thailand Thailand ( ), historically known as Siam () and officially the Kingdom of Thailand, is a country in Southeast Asia, located at the centre of the Indochinese Peninsula, spanning , with a population of almost 70 million. The country is b ...
,
Laos Laos (, ''Lāo'' )), officially the Lao People's Democratic Republic ( Lao: ສາທາລະນະລັດ ປະຊາທິປະໄຕ ປະຊາຊົນລາວ, French: République démocratique populaire lao), is a socialist s ...
, and
Cambodia Cambodia (; also Kampuchea ; km, កម្ពុជា, UNGEGN: ), officially the Kingdom of Cambodia, is a country located in the southern portion of the Indochinese Peninsula in Southeast Asia, spanning an area of , bordered by Thailand ...
, the traditional system of noting hours is the six-hour clock. This reckons each of a day's 24 hours apart from noon as part of a fourth of the day. 7 am was the first hour of the first half of daytime; 1 pm the first hour of the latter half of daytime; 7 pm the first hour of the first half of nighttime; and 1 am the first hour of the latter half of nighttime. This system existed in the
Ayutthaya Kingdom The Ayutthaya Kingdom (; th, อยุธยา, , IAST: or , ) was a Siamese kingdom that existed in Southeast Asia from 1351 to 1767, centered around the city of Ayutthaya, in Siam, or present-day Thailand. The Ayutthaya Kingdom is consi ...
, deriving its current phrasing from the practice of publicly announcing the daytime hours with a gong and the nighttime hours with a
drum The drum is a member of the percussion group of musical instruments. In the Hornbostel-Sachs classification system, it is a membranophone. Drums consist of at least one membrane, called a drumhead or drum skin, that is stretched over a ...
. It was abolished in Laos and Cambodia during their
French occupation French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Fran ...
and is uncommon there now. The Thai system remains in informal use in the form codified in 1901 by
King Chulalongkorn Chulalongkorn ( th, จุฬาลงกรณ์, 20 September 1853 – 23 October 1910) was the fifth monarch of Siam under the House of Chakri, titled Rama V. He was known to the Siamese of his time as ''Phra Phuttha Chao Luang'' (พร� ...
.


India

The
Vedas upright=1.2, The Vedas are ancient Sanskrit texts of Hinduism. Above: A page from the '' Atharvaveda''. The Vedas (, , ) are a large body of religious texts originating in ancient India. Composed in Vedic Sanskrit, the texts constitute th ...
and
Puranas Purana (; sa, , '; literally meaning "ancient, old"Merriam-Webster's Encyclopedia of Literature (1995 Edition), Article on Puranas, , page 915) is a vast genre of Indian literature about a wide range of topics, particularly about legends an ...
employed units of time based on the sidereal day (''nakṣatra ahorātram''). This was variously divided into 30 ''muhūtras'' of 48 minutes each or 60 ''dandas'' or ''nadís'' of 24 minutes each. The solar day was later similarly divided into 60 ''ghaṭikás'' of about the same duration, each divided in turn into 60 ''vinadis''. The Sinhalese followed a similar system but called their sixtieth of a day a ''peya''.


Derived measures

* air changes per hour (ACH), a measure of the replacements of air within a defined space used for indoor air quality * ampere hour (Ah), a measure of electrical charge used in
electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between electrical potential difference, as a measurable and quantitative phenomenon, and identifiable chemical change, with the potential difference as an out ...
* BTU-hour, a measure of power used in the power industry and for air conditioners and heaters * credit hour, a measure of an academic
course Course may refer to: Directions or navigation * Course (navigation), the path of travel * Course (orienteering), a series of control points visited by orienteers during a competition, marked with red/white flags in the terrain, and corresponding ...
's contracted instructional time per week for a semester * horsepower-hour (hph), a measure of energy used in the railroad industry *
hour angle In astronomy and celestial navigation, the hour angle is the angle between two planes: one containing Earth's axis and the zenith (the '' meridian plane''), and the other containing Earth's axis and a given point of interest (the ''hour circle' ...
, a measure of the angle between the meridian plane and the hour circle passing through a certain point used in the equatorial coordinate system * kilometres per hour (km/h), a measure of land speed * kilowatt-hour (kWh), a measure of energy commonly used as an electrical billing unit *
knot A knot is an intentional complication in cordage which may be practical or decorative, or both. Practical knots are classified by function, including hitches, bends, loop knots, and splices: a ''hitch'' fastens a rope to another object; a ...
(kn), a measure of
nautical mile A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. Historically, it was defined as the meridian arc length corresponding to one minute ( of a degree) of latitude. Tod ...
s per hour, used for maritime and aerial speed * man-hour, the amount of work performed by the average worker in one hour, used in productivity analysis * metre per hour (m/h), a measure of slow speeds * mile per hour (mph), a measure of land speed * passengers per hour per direction (p/h/d), a measure of the capacity of
public transport Public transport (also known as public transportation, public transit, mass transit, or simply transit) is a system of transport for passengers by group travel systems available for use by the general public unlike private transport, typi ...
ation systems * pound per hour (PPH), a measure of
mass flow Mass flow, also known as mass transfer and bulk flow, is the movement of fluids down a pressure or temperature gradient,Moyes & Schulte (2008). Principles of Animal Physiology. Pearson Benjamin Cummings. San Francisco, California particularly in ...
used for engines' fuel flow * work or working hour, a measure of working time used in various regulations, such as those distinguishing part- and
full-time Full-time or Full Time may refer to: * Full-time job, employment in which a person works a minimum number of hours defined as such by their employer * Full-time mother, a woman whose work is running or managing her family's home * Full-time fa ...
employment and those limiting truck drivers' working hours or
hours of service Hours of Service (HOS) regulations are issued by the Federal Motor Carrier Safety Administration (FMCSA) and govern the working hours of anyone operating a commercial motor vehicle (CMV) in the United States. These regulations apply to truck dr ...


See also

*
Liturgy of the Hours The Liturgy of the Hours (Latin: ''Liturgia Horarum'') or Divine Office (Latin: ''Officium Divinum'') or ''Opus Dei'' ("Work of God") are a set of Catholic prayers comprising the canonical hours, often also referred to as the breviary, of the ...
* Horology * Horae, the deified hours of ancient Greece and Rome * Hexadecimal hour, a proposed unit lasting 1h 30min * Decimal hour or deciday, a French Revolutionary unit lasting 2h 24min * Golden Hour & Blue Hour in photography * Metric time


Notes


References


Bibliography

* * * * * * * * * * * * * * * * *


Further reading

* * Christopher Walker (ed.), ''Astronomy before the Telescope''. London: British Museum Press, 1996.


External links


World time zones


{{Authority control Orders of magnitude (time) Units of time