# Hour

htime of dayhrhrsstoundItalian hours22nd hour24-hour60 minutescounting hours
An hour (symbol: h; also abbreviated hr.) is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions.wikipedia
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### Second

ssecmegasecond
An hour (symbol: h; also abbreviated hr.) is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions. The hour was subsequently divided into 60 minutes, each of 60 seconds.
The second (symbol: s, abbreviation: sec) is the base unit of time in the International System of Units (SI), commonly understood and historically defined as 1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each.

### Minute

minmmins.
The hour was subsequently divided into 60 minutes, each of 60 seconds.
The minute is a unit of time usually equal to 1⁄60 (the first sexagesimal fraction ) of an hour, or 60 seconds.

### Non-SI units mentioned in the SI

accepted for use with SIAccepted for use with the SIaccepted unit
In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds.

### 24-hour clock

24-hour24-hour notation24-hour format
Hours on a 24-hour clock ("military time") are expressed as "hundred" or "hundred hours".
The 24-hour clock is the convention of time keeping in which the day runs from midnight to midnight and is divided into 24 hours, indicated by the hours passed since midnight, from 0 to 23.

### Time

temporaldurationsequence of events
An hour (symbol: h; also abbreviated hr.) is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions.
A minute (min) is 60 seconds in length, and an hour is 60 minutes in length.

### Sundial

sundialssun dialsun clock
The later division of the day into 12 hours was accomplished by sundials marked with ten equal divisions. Astrolabes, sundials, and astronomical clocks sometimes show the hour length and count using some of these older definitions and counting methods.
A sundial is a device that tells the time of day when there is sunlight by the apparent position of the Sun in the sky.

### Metric system

metricmetric unitsmetric unit
An hour (symbol: h; also abbreviated hr.) is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions. In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds.
Prefixes are not usually used to indicate multiples of a second greater than 1; the non-SI units of minute, hour and day are used instead.

### Year

myaMay
Like Old English tīd and stund, hṓrā was originally a vaguer word for any span of time, including seasons and years.
Cognates also descended from the same Proto-Indo-European noun (with variation in suffix ablaut) are Avestan yārǝ "year", Greek ὥρα (hṓra) "year, season, period of time" (whence "hour"), Old Church Slavonic jarŭ, and Latin hornus "of this year".

### Day

ddiurnaldays
An hour (symbol: h; also abbreviated hr.) is a unit of time conventionally reckoned as 1⁄24 of a day and scientifically reckoned as 3,599–3,601 seconds, depending on conditions.

### Thai six-hour clock

Six-hour clockThai 6-hour clock6-hour clock
In Thailand, Laos, and Cambodia, the traditional system of noting hours is the six-hour clock.
Like other common systems, it counts twenty-four hours in a day, but divides the day into four quarters, counting six hours in each.

### Tide (disambiguation)

stund
It displaced tide tīd, "time" and stound stund, span of time.

### Water clock

clepsydrawater clockswater-clock
By the time of Amenhotep III, the priests at Karnak were using water clocks to determine the hours.
It featured a 24-hour mechanized clepsydra and indicators for the eight winds from which the tower got its name, and it displayed the seasons of the year and astrological dates and periods.

### Atet

bargesolar barge
By the New Kingdom, each hour was conceived as a specific region of the sky or underworld through which Ra's solar barge travelled.
Each twelfth of his journey formed one of the twelve Egyptian hours of the day, each overseen by a protective deity.

### Decimal time

10-hour clockdecimal clocksdecimal multiple
During the French Revolution, a general decimalization of measures was enacted, including decimal time between 1793 and 1795.
This term is often used specifically to refer to the time system used in France for a few years beginning in 1792 during the French Revolution, which divided the day into 10 decimal hours, each decimal hour into 100 decimal minutes and each decimal minute into 100 decimal seconds (100000 decimal seconds per day), as opposed to the more familiar UTC time standard, which divides the day into 24 hours, each hour into 60 minutes and each minute into 60 seconds (86400 SI seconds per day).

### Hour record

world hour recordUCI Hour RecordBest Hour Performance
The hour record for the greatest distance travelled by a cyclist within the span of an hour is one of cycling's greatest honours.
The hour record is the record for the longest distance cycled in one hour on a bicycle from a stationary start.

### Clock

timepiecemechanical clockanalog clock
When mechanical clocks 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 more sophisticated astronomical clocks would have had moving dials or hands, and would have shown the time in various time systems, including Italian hours, canonical hours, and time as measured by astronomers at the time.

### Prague astronomical clock

Prague OrlojAstronomical ClockOrloj
The St Mark's Clock in Venice, and the Orloj in Prague are famous examples.
The clock mechanism has three main components — the astronomical dial, representing the position of the Sun and Moon in the sky and displaying various astronomical details; statues of various Catholic saints stand on either side of the clock; "The Walk of the Apostles", a clockwork hourly show of figures of the Apostles and other moving sculptures, notably a figure of a skeleton, representing Death, striking the time; and a calendar dial with medallions representing the months.

### St Mark's Clock

see the separate article on the clock
The St Mark's Clock in Venice, and the Orloj in Prague are famous examples.
Driven by weights, with a foliot escapement, the clock controlled both the bell-ringing shepherds on the tower, who would have rung the bell between 1 and 24 times to sound the Italian hours, and a carousel which showed the procession of the Magi, preceded by an angel blowing a trumpet.

### Hindu units of time

mahayugaSrishtiVedic timekeeping
The Vedas and Puranas employed units of time based on the sidereal day (nakṣatra ahorātram).

### Miles per hour

mphmile per hourm.p.h.
Miles per hour (mph, MPH or mi/h) is a British imperial and United States customary unit of speed expressing the number of statute miles covered in one hour.

### Kilometres per hour

km/hkilometers per hourkilometre per hour
The kilometre per hour (SI symbol: km/h; abbreviations: kph, kmph, km/hr) is a unit of speed, expressing the number of kilometres travelled in one hour.

### Metric time

centidaymetrication of the dayMilliday
Other units of time: minute, hour, and day, are accepted for use with SI, but are not part of it.

### Metre per hour

meter per hourmeters per hour
By definition, an object travelling at a speed of 1 m/h for an hour would move 1 metre.

### Astrolabe

astrolabesAstrolabAstrolabium
Astrolabes, sundials, and astronomical clocks sometimes show the hour length and count using some of these older definitions and counting methods.
The rim of the mater is typically graduated into hours of time, degrees of arc, or both.