Unequal Hours
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Unequal hours are the division of the
daytime Daytime or day as observed on Earth is the period of the day during which a given location experiences Daylight, natural illumination from direct sunlight. Daytime occurs when the Sun appears above the local horizon, that is, anywhere on the ...
and the
nighttime Night, or nighttime, is the period of darkness when the Sun is below the horizon. Sunlight illuminates one side of the Earth, leaving the other in darkness. The opposite of nighttime is daytime. Earth's rotation causes the appearance of su ...
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 axial tilt, tilted orbit around the Sun. In temperat ...
. 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 5th to the late 15th centuries, similarly to the post-classical period of global history. It began with the fall of the Western Roman Empire and ...
by the now common ones of equal duration. The first temporal hour of daylight begins at sunrise, the first of night at
sunset Sunset (or sundown) is the disappearance of the Sun at the end of the Sun path, below the horizon of the Earth (or any other astronomical object in the Solar System) due to its Earth's rotation, rotation. As viewed from everywhere on Earth, it ...
. For example, if daylight and night are each divided into twelve temporal hours, midday and
midnight Midnight is the transition time from one day to the next – the moment when the date changes, on the local official clock time for any particular jurisdiction. By clock time, midnight is the opposite of noon, differing from it by 12 hours. ...
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 equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...
, the duration of daylight depends on the
latitude In geography, latitude is a geographic coordinate system, geographic 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 t ...
and 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 axial tilt, tilted orbit around the Sun. In temperat ...
. At 49° north/south latitude (e.g., in
Karlsruhe Karlsruhe ( ; ; ; South Franconian German, South Franconian: ''Kallsruh'') is the List of cities in Baden-Württemberg by population, third-largest city of the States of Germany, German state of Baden-Württemberg, after its capital Stuttgart a ...
), 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 equinoxes. From 66.5° north/south latitude ( polar circles) the sun no longer sets (the
horizon The horizon is the apparent curve that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This curve divides all viewing directions based on whethe ...
) 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 Ancient Egypt () was a cradle of civilization concentrated along the lower reaches of the Nile River in Northeast Africa. It emerged from prehistoric Egypt around 3150BC (according to conventional Egyptian chronology), when Upper and Lower E ...
. 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 Western culture, also known as Western civilization, European civilization, Occidental culture, Western society, or simply the West, refers to the Cultural heritage, internally diverse culture of the Western world. The term "Western" encompas ...
they were adopted from the
Roman calendar The Roman calendar was the calendar used by the Roman Kingdom and Roman Republic. Although the term is primarily used for Rome's pre-Julian calendars, it is often used inclusively of the Julian calendar established by Julius Caesar in 46&nbs ...
and were adopted in the
Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
an
Medieval In the history of Europe, the Middle Ages or medieval period lasted approximately from the 5th to the late 15th centuries, similarly to the post-classical period of World history (field), global history. It began with the fall of the West ...
era. They had particular relevance in the fixed daily schedule of the
monastic Monasticism (; ), also called monachism or monkhood, is a religious way of life in which one renounces worldly pursuits to devote oneself fully to spiritual activities. Monastic life plays an important role in many Christian churches, especially ...
orders. 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'' ( ; , ), also transliterated as ''halacha'', ''halakhah'', and ''halocho'' ( ), is the collective body of Jewish religious laws that are derived from the Written and Oral Torah. ''Halakha'' is based on biblical commandments ('' mi ...
), hence the Jewish Halachic division of hours. Mechanical
clock A clock or chronometer is a device that measures and displays time. The clock is one of the oldest Invention, human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month, a ...
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 A sundial is a horology, horological device that tells the time of day (referred to as civil time in modern usage) when direct sunlight shines by the position of the Sun, apparent position of the Sun in the sky. In the narrowest sense of the ...
with as hand was once used. The position of the Sun, which varied throughout the year, served as a parameter on which the varying duration of the temporal hours during the year depended. Many astronomical clocks 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
verge escapement The verge (or crown wheel) escapement is the earliest known type of mechanical escapement, the mechanism in a mechanical clock that controls its rate by allowing the gear train to advance at regular intervals or 'ticks'. Verge escapements were us ...
(Waag) was changed, for example, in 26 steps (i.e., half the numerical value of 52 weeks). In the weeks of the equinox, both clocks could be operated with the middle weight position on the balance.


See also

* Twilight * Terminator (solar) * (in German) * Time perception *
Civil time In modern usage, civil time refers to statutory time as designated by civilian authorities. Modern civil time is generally national standard time in a time zone at a UTC offset, fixed offset from Coordinated Universal Time (UTC), possibly adjusted ...
* equinoctial hours * * Danna * Julian day * Chronobiology * {{Ill, Ancient Egyptian day, de, Tag_(Altes_Ägypten)


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


Die Temporalstunden
Jewish law Timekeeping Pages with unreviewed translations History of timekeeping