Unequal hours are the division of the light day and 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 ...

into 12 sections each, whatever the

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 ...

. They are also called temporal hours, seasonal hours, biblical or Jewish hours, as well as ancient or Roman hours (). They are ''unequal duration'' periods of time because days are longer and nights shorter in summer than in winter. Their use in everyday life was replaced in the late

Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...

by the now common ones of equal duration. The first temporal hour of daylight begins at

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 A ...

, the first of night at Sunset. For example, if daylight and night are each divided into twelve temporal hours,

Midday Noon (or midday) is 12 o'clock in the daytime. It is written as 12 noon, 12:00 m. (for meridiem, literally 12:00 noon), 12 p.m. (for post meridiem, literally "after noon"), 12 pm, or 12:00 (using a 24-hour clock) or 1200 (military time). Solar ...

and Midnight are each the beginning of the seventh hour. A clock that displays the temporal hours is called a temporal clock.

Astronomical basics

To the concept of ''light day'' corresponds the astronomical concept '' Day arc of the Sun''. With the exception of the equator, the duration of daylight depends on the

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 pol ...

and the

. At 49° north/south latitude (e.g., in

Karlsruhe Karlsruhe ( , , ; South Franconian: ''Kallsruh'') is the third-largest city of the German state (''Land'') of Baden-Württemberg after its capital of Stuttgart and Mannheim, and the 22nd-largest city in the nation, with 308,436 inhabitants. ...

), it varies between 16 equinoctal hours in summer and 8 equinoctial hours in winter. Due to the continuous change of the duration of daylight over the course of the year, the duration of the day division, i.e. the temporal day hours and the temporal night hours, also changes over the year. The temporal hours of day and night are equal only at the spring and autumn

equinox A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears 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" and se ...

es. From 66.5° north/south latitude (

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 d ...

s) the sun no longer sets (the horizon) every day in summer and rises every day in winter. Day does not occur.

History

Temporal hours were common in many cultures. A division of day and night into twelve hours each was first recorded in Ancient Egypt. A similar division of day and night was later made in the Mediterranean Basin from about Classical Greek Antiquity into twelve temporal hours each (). In

Western culture Leonardo da Vinci's ''Vitruvian Man''. Based on the correlations of ideal Body proportions">human proportions with geometry described by the ancient Roman architect Vitruvius in Book III of his treatise ''De architectura''. image:Plato Pio-Cle ...

they were adopted from the

Roman calendar The Roman calendar was the calendar used by the Roman Kingdom and Roman Republic. The term often includes the Julian calendar established by the reforms of the dictator Julius Caesar and emperor Augustus in the late 1stcenturyBC and sometim ...

and were adopted in the

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

Medieval In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...

era. They had particular relevance in the fixed daily schedule of the

monastic Monasticism (from Ancient Greek , , from , , 'alone'), also referred to as monachism, or monkhood, is a religion, religious way of life in which one renounces world (theology), worldly pursuits to devote oneself fully to spiritual work. Monastic ...

orders Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

. This division of time allowed the work of the day -such as eating, praying, or working -to always be performed at the same (temporal) hour, regardless of season ( Prayer of the Hours). This chronology is used by Jewish religious law (

Halacha ''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 ...

), hence ''

Jewish Jews ( he, יְהוּדִים, , ) or Jewish people are an ethnoreligious group and nation originating from the Israelites Israelite origins and kingdom: "The first act in the long drama of Jewish history is the age of the Israelites""The ...

'' or '' Biblical Division of hours''. 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 t ...

s encouraged the adoption of equinoctial hours.

Temporal time

For the display of temporal hoursKarlheinz Deußer: ''Temporaluhren: Die Suche nach mechanischen Uhren, die mit Temporalstunden liefen.'' 2012. almost exclusively the Sundial with as hand was once used. The Sun position, which varied throughout the year, served as a parameter on which the varying duration of the temporal hours during the year depended. Many

astronomical clock An astronomical clock, horologium, or orloj is a clock with special mechanisms and dials to display astronomical information, such as the relative positions of the Sun, Moon, zodiacal constellations, and sometimes major planets. Definition ...

s created during the transition to the equal-duration equinoctial hours display temporal hours in addition to the new equal-duration hours. Even where temporal hours continued to be used (especially in monasteries), the mechanical clock was used. This required two different settings for the day and for the night, or one clock each for the day and the night. For the latter, the speed of the

Waag A weighhouse or weighing house is a public building at or within which goods are weighed. Most of these buildings were built before 1800, prior to the establishment of international standards for weights, and were often a large and representative ...

was changed, for example, in 26 steps (i.e., half the numerical value of 52 weeks). In the weeks of the

Equinox A solar equinox is a moment in time when the Sun crosses the Earth's equator, which is to say, appears 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" and se ...

, both clocks could be operated with the middle weight position on the balance.

Bibliography

* Karlheinz Deußer: ''Temporaluhren: Die Suche nach mechanischen Uhren, die mit Temporalstunden liefen.'' In: ''Jahresschrift der deutschen Gesellschaft für Chronometrie.'' Band 51, 2012, S. 143–160. * Jürgen Osing: ''Hieratische Papyri aus Tebtunis I (Carsten Niebuhr Institute of Ancient Eastern Studies Copenhagen)''. Museum Tusculanum Press, Copenhagen 1998, ISBN 8-7728-9280-3. * Rudolf Wendorff: ''Zeit und Kultur. Geschichte des Zeitbewusstseins in Europa''. Westdeutscher Vlg, Wiesbaden 1980, ISBN 3-531-11515-4.

References

External links