The hour (symbol: h) is a unit of time. For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of It is not an SI unit but is accepted for use with the SI.

Contents 1 Definition 2 Etymology 3 History 4 Counting hours 5 See also 6 References 7 Further reading

Definition

In modern usage, an hour is a unit of time 60 minutes, or 3,600 seconds in length. For other uses see Time (disambiguation Time is a component of a measuring system used to sequence events to compare the durations of A minute is a Unit of measurement of Time or of Angle. The minute is a unit of Time equal to 1/60th of an Hour or 60 The second ( SI symbol s) sometimes abbreviated sec, is the name of a unit of Time, and is the International System of Units It is approximately 1/24 of a median Earth day. EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 A day (symbol d is a unit of Time equivalent to 24 Hours and the duration of a single Rotation of planet Earth with respect to the

Etymology

Further information: horoscopy and Year#Etymology

Middle English ure first appears in the 13th century, as a loanword from Old French ure, ore, form Latin hora, ultimately from Greek ὥρα "season, time of day, hour". In Astrology, a horoscope is a chart or diagram representing the positions of the Sun Moon planets the Astrological aspects, and sensitive angles A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun Middle English is the name given by Historical linguistics to the diverse forms of the English language spoken between the Norman invasion of Old French was the Romance Dialect continuum spoken in territories which span roughly the northern half of modern France and parts of modern Belgium Middle English ure, Anglo-French houre replaced Old English tíd (which survives as Modern English tide) and stund (Old High German stunta, from a Germanic *stundō "time, interval, while"). Characteristics A tide is a repeated cycle of sea level changes in the following stages Over several hours the water rises or advances up a beach in the flood

Greek ὥρα is cognate to English year, both from a PIE *i̯ēro- "year, summer". A year (from Old English gēr) is the time between two recurrences of an event related to the Orbit of the Earth around the Sun

History

The hour was originally defined in ancient civilizations (including those of Egypt, Sumer, India, and China) as either one twelfth of the time between sunrise and sunset or one twenty-fourth of a full day. In either case the division reflected the widespread use of a duodecimal numbering system. The duodecimal system (also known as base -12 or dozenal) is a Numeral system using twelve as its base. The importance of 12 has been attributed to the number of lunar cycles in a year, and also to the fact that humans have 12 finger bones (phalanges) on one hand (3 on each of 4 fingers). The name Phalanx (plural phalanges) is commonly given to the Bones that form Fingers and Toes In Primates such as Humans ^[1] (It is possible to count to 12 with your thumb touching each finger bone in turn. ) There is also a widespread tendency to make analogies among sets of data (12 months, 12 zodiacal signs, 12 hours, a dozen).

The Ancient Egyptian civilization is usually credited with establishing the division of the night into 12 parts, although there were many variations over the centuries. Astronomers in the Middle Kingdom (9th and 10th Dynasties) observed a set of 36 decan stars throughout the year. In Astrology, a decan is the subdivision of a sign The concept of decans originated with the ancient Chaldeans when they divided the 360 degree circle of the These star tables have been found on the lids of coffins of the period. The heliacal rising of the next decan star marked the start of a new civil week, which was then 10 days. The heliacal rising of a Star (or other body such as the Moon, a Planet or a Constellation) occurs when it first becomes visible above the eastern The period from sunset to sunrise was marked by 18 decan stars. Three of these were assigned to each of the two twilight periods, so the period of total darkness was marked by the remaining 12 decan stars, resulting in the 12 divisions of the night. The time between the appearance of each of these decan stars over the horizon during the night would have been about 40 modern minutes. During the New Kingdom, the system was simplified, using a set of 24 stars, 12 of which marked the passage of the night.

Earlier definitions of the hour varied within these parameters:

• One twelfth of the time from sunrise to sunset. As a consequence, hours on summer days were longer than on winter days, their length varying with latitude and even, to a small extent, with the local weather (since it affects the atmosphere's index of refraction). Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the Temperature and layers The temperature of the Earth's atmosphere varies with altitude the mathematical relationship between temperature and altitude varies among five Refraction is the change in direction of a Wave due to a change in its Speed. For this reason, these hours are sometimes called temporal, seasonal, or unequal hours. Romans and Greeks and Jews used this definition; so did the ancient Chinese and Japanese. Rome ( Roma ˈroma Roma is the capital city of Italy and Lazio, and is Italy's largest and most populous city with more than 2 Greece (Ελλάδα transliterated: Elláda, historically, Ellás,) officially the Hellenic Republic (Ελληνική Δημοκρατία The Romans and Greeks also divided the night into three or four night watches, but later the night (the time between sunset and sunrise) was also divided into twelve hours. When, in post-classical times, a clock showed these hours, its period had to be changed every morning and evening (for example by changing the length of its pendulum), or it had to keep to the position of the Sun on the ecliptic (see Prague Astronomical Clock). Circadian Locomotor Output Cycles Kaput, or Clock is a gene which encodes proteins regulating Circadian rhythm. The Prague Astronomical Clock or Prague Orloj (Pražský orloj ɔrlɔi is a Medieval Astronomical clock located in Prague, the capital of
• One twenty-fourth of the apparent solar day (between one noon and the next, or between one sunset and the next). Solar times are measures of the apparent position of the Sun on the Celestial sphere. As a consequence hours varied a little, as the length of an apparent solar day varies throughout the year. When a clock showed these hours it had to be adjusted a few times in a month. These hours were sometimes referred to as equal or equinoctial hours.
• One twenty-fourth of the mean solar day. See mean sun for more information on the difference to the apparent solar day. Solar times are measures of the apparent position of the Sun on the Celestial sphere. When an accurate clock showed these hours it virtually never had to be adjusted. However, as the Earth's rotation slows down, this definition has been abandoned. See UTC.

Counting hours

There are different ways of counting the hours:

• In ancient and medieval cultures, in which the division between night and day mattered far more than in societies with widespread use of artificial light, the counting of hours started with sunrise. So sunrise was always exactly at the beginning of the first hour (the zero hour), noon at the end of the sixth hour and sunset exactly at the end of the twelfth hour. This meant that the length of hours varied with the season. This type of counting is sometimes referred to, on astrolabes and astronomical clocks, for example, as "Babylonian" or temporal hours. The astrolabe is a historical Astronomical instrument used by classical astronomers, Navigators An astronomical clock is a Clock with special Mechanisms and Dials to display Astronomical information such as the relative positions of It is also the system used in Jewish religious law (Halakha) and frequently called Talmudic hour ("Sha'a Zemanit") in a variety of texts. Halakha ( הלכה; alternative transliterations include Halocho and Halacha) is the collective body of Jewish Religious law

The talmudic hour is the division of time elapsed from sunrise to sunset by 12, therefore being longer at summer than in winter.

• In so-called Italian time, or "Italian hours", the first hour started with the Angelus at sunset (or the end of dusk, i. The Angelus ( Latin for Angel) is a Christian devotion in memory of the Incarnation. 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 see how much time they had to finish their day's work without artificial light. It was already widely used in Italy by the 14th century and lasted until the mid-18th century (was officially abolished in 1755), or in some regions, customary, until the mid-19th century. Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest The 18th century lasted from 1701 to 1800 in the Gregorian calendar, in accordance with the Anno Domini / Common Era numbering system Year 1755 ( MDCCLV) was a Common year starting on Wednesday (link will display the full calendar of the Gregorian calendar (or The 19th century of the Common Era began on January 1, 1801 and ended on December 31, 1900, according to the Gregorian calendar ^[2] It was also used in Poland and Bohemia until the 17th century. Poland (Polska officially the Republic of Poland Bohemia (Čechy; Bohemia Czechy is a historical region in central Europe, occupying the western two-thirds of the traditional Czech Lands, currently the As a means of recording the passage of Time, the 17th Century was that Century which lasted from 1601 - 1700 in the Gregorian calendar The system of Italian hours can be seen on a number of clocks in Italy, where the dial is numbered from 1 to 24 in either Roman or Arabic numerals. The St Mark's Clock in Venice is a famous example. St Mark's Clock is the Clock housed in the St Mark's Clocktower, on St Mark's Square in Venice, adjoining the Procuratie Vecchie.
• The medieval Islamic day began at sunset. For other meanings including people named 'Islam' see Islam (disambiguation. The first prayer of the day (maghrib) was to be performed between sunset and the end of twilight. Maghrib (مَغْرِب is the fourth daily Salat in Islam, offered at sunset
• 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, differing according to the equation of time (by up to about fifteen minutes either way). Solar times are measures of the apparent position of the Sun on the Celestial sphere. The equation of time is the difference over the course of a year between time as read from a Sundial and time as read from a Clock, measured in an ideal situation At the equinoxes sunrise is around 6 A. An equinox is the event of the Sun passing over the Earth's equator in its annual cycle M. (ante meridiem, before noon), and sunset around 6 P. M. (post meridiem, after noon).
• In the modern 24-hour clock, counting the hours starts at midnight and hours are numbered from 0 to 23. Description A time of day is written in the 24-hour notation in the form hhmm (for example 0123 or hhmmss (for example 012345 where hh (00 to 23 is the decimal number 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.
• For many centuries, up to 1925, astronomers counted the hours and days from noon, because it was the easiest solar event to measure accurately. Year 1925 ( MCMXXV) was a Common year starting on Thursday (link will display the full calendar of the Gregorian calendar. 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. The Julian date (JD is the interval of time in days and fractions of a day since 4713 B

Sunrise and sunset are much more conspicuous points in the day than noon or midnight; starting to count at these times was, for most people in most societies, much easier than starting at noon or midnight. However, with 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, sundials, and astronomical clocks sometimes show the hour length and count using some of the older definitions and counting methods. The astrolabe is a historical Astronomical instrument used by classical astronomers, Navigators A sundial is a device that measures time by the position of the Sun. An astronomical clock is a Clock with special Mechanisms and Dials to display Astronomical information such as the relative positions of

See also

• Canonical hours

References

• "Astronomy before the telescope". Ed. Christopher Walker. London: British Museum Press, 1996.

Further reading

• Gerhard Dohrn-van Rossum (1996). History of the hour: clocks and modern temporal orders. University of Chicago Press. ISBN 0226155102.  

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