AskDefine | Define hour

Dictionary Definition



1 a period of time equal to 1/24th of a day; "the job will take more than an hour" [syn: hr, 60 minutes]
2 clock time; "the hour is getting late" [syn: time of day]
3 a special and memorable period; "it was their finest hour"
4 distance measured by the time taken to cover it; "we live an hour from the airport"; "its just 10 minutes away" [syn: minute]

User Contributed Dictionary



Via , from heure, from hora, from ὥρα (hora) "any time or period, whether of the year, month, or day".


  • , /aʊə(ɹ)/, /aU@(r)/
  • , /aʊɹ/ or /aʊɚ/, /aUr/
  • Rhymes with: -aʊə(r)


  • our (depending on accent)


  1. A time period of sixty minutes; one twenty-fourth of a day.
    I spent an hour at lunch.
  2. The time.
    The hour grows late and I must go home.


time period of sixty minutes
the time

Extensive Definition

The hour (symbol: h) is a unit of time. It is not an SI unit but is accepted for use with the SI.


In modern usage, an hour is a unit of time 60 minutes, or 3,600 seconds in length. It is approximately 1/24 of a median Earth day.


Middle English ure first appears in the 13th century, as a loanword from Old French ure, ore, form Latin hora, ultimately from Greek "season, time of day, hour". 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").
Greek is cognate to English year, both from a PIE "year, summer".


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 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). (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. 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 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). 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. 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).
  • One twenty-fourth of the apparent solar day (between one noon and the next, or between one sunset and the next). 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. 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. It is also the system used in Jewish religious law (Halakha) and frequently called Talmudic hour ("Sha'a Zemanit") in a variety of texts.
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.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. It was also used in Poland and Bohemia until the 17th century. 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.
  • The medieval Islamic day began at sunset. The first prayer of the day (maghrib) was to be performed between sunset and the end of twilight.
  • 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). At the equinoxes sunrise is around 6 A.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. 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. 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.
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.

See also


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

Further reading

  • History of the hour: clocks and modern temporal orders
hour in Tosk Albanian: Stunde
hour in Arabic: ساعة (وحدة)
hour in Official Aramaic (700-300 BCE): ܫܥܬܐ
hour in Asturian: Hora
hour in Min Nan: Tiám-cheng
hour in Bosnian: Sat (mjerna jedinica)
hour in Bulgarian: Час
hour in Catalan: Hora
hour in Czech: Hodina
hour in Danish: Time (enhed)
hour in German: Stunde
hour in Estonian: Tund
hour in Modern Greek (1453-): Ώρα
hour in Spanish: Hora
hour in Esperanto: Horo
hour in Basque: Ordu
hour in Persian: ساعت (زمان)
hour in French: Heure (temps)
hour in Western Frisian: Oere
hour in Galician: Hora
hour in Korean: 시간 (단위)
hour in Hindi: घंटा
hour in Croatian: Sat
hour in Icelandic: Klukkustund
hour in Italian: Ora (unità di misura)
hour in Hebrew: שעה
hour in Swahili (macrolanguage): Saa
hour in Haitian: Lè (tan)
hour in Latin: Hora
hour in Luxembourgish: Stonn
hour in Lithuanian: Valanda
hour in Lingala: Ngonga
hour in Hungarian: Óra (időegység)
hour in Dutch: Uur
hour in Japanese: 時間 (単位)
hour in Cree: Kâ-isiwepahki
hour in Norwegian: Time (tidsenhet)
hour in Norwegian Nynorsk: Time
hour in Narom: Heure
hour in Low German: Stünn
hour in Polish: Godzina
hour in Portuguese: Hora
hour in Kölsch: Shtůndt
hour in Romanian: Oră
hour in Quechua: Ura
hour in Russian: Час
hour in Simple English: Hour
hour in Slovak: Hodina
hour in Slovenian: Ura
hour in Serbian: Сат
hour in Serbo-Croatian: Sat
hour in Finnish: Tunti
hour in Swedish: Timme
hour in Tamil: மணித்தியாலம்
hour in Thai: ชั่วโมง
hour in Vietnamese: Giờ
hour in Turkish: Saat (zaman)
hour in Ukrainian: Година
hour in Urdu: گھنٹہ
hour in Yoruba: Wákàtí
hour in Contenese: 鐘頭
hour in Chinese: 小时

Synonyms, Antonyms and Related Words

abundant year, academic year, annum, bell, bissextile year, calendar month, calendar year, century, common year, day, decade, decennary, decennium, defective year, fateful moment, fiscal year, fortnight, instant, interval, juncture, kairos, leap year, lunar month, lunar year, lunation, luster, lustrum, man-hour, microsecond, millennium, millisecond, minute, moment, moment of truth, month, moon, period, point, pregnant moment, psychological moment, quarter, quinquennium, regular year, season, second, semester, session, sidereal year, solar year, space, span, spell, stage, stretch, sun, term, the time, time, time lag, time of day, time signal, trimester, twelvemonth, week, weekday, while, year
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