Temporal hour
Temporal hours or Seasonal hours are the former division of the light day and the night into 12 sections each, whatever the season. They are also called biblical or Jewish hours as well as ancient or Roman hours, Latin: horae temporales. They are unequal length periods of time because the light day is longer in summer than in winter (vice versa for night). Their use in everyday life was replaced from the late Middle Ages by the now common ones of equal length.
The first temporal hour of daylight begins at Sunrise, the first of night at Sunset. For example, if daylight and night are each divided into twelve temporal hours, Midday and Midnight are each the beginning of the seventh hour.
A clock that displays the temporal hours is called a temporal clock.
Astronomical basics[edit]
To the concept of light day corresponds the astronomical concept Day arc of the Sun. With the exception of the equator, the length of the light day depends on the geographic latitude and the season. At 49° north/south latitude (e.g., in Karlsruhe), it varies between 16 equinoctal hours in summer and 8 equinoctial hours in winter.
Due to the continuous change of the lengths of daylight and night in the course of the year, the lengths of the day division, i.e. the temporal day hours and the temporal night hours, also change over the year.
The temporal hours of day and night are equal only at the beginning of spring and autumn (equinox). In summer, daytime hours are longer than nighttime hours, and vice versa in winter.
From 66.5° north/south latitude (Polar circles) the sun no longer sets (the horizon) every day in summer and no longer rises every day in winter - there is no longer the "day" in the sense of the term. For more on this, see Rise (astronomy).
History[edit]
Temporal hours were common in many cultures. A division of day and night into twelve hours each is first attested in Ancient Egypt. A similar division of the light day and night was later made in the Mediterranean Basin from about Classical Greek Antiquity into twelve temporal hours each (Ancient Greek: ὥραι καιρικαί, romanized: horai kairikai).
In our culture they were adopted from the Roman calendar and were used in the European Medieval and beyond. They had particular relevance in the fixed daily schedule of the monastic 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, no matter how long the light day was (Prayer of the Hours).
This chronology is also used by Jewish religious law (Halacha), hence Jewish or Biblical Division of hours.
As mechanical clocks became more widespread and important, temporal hours were replaced by equinoctial hours, which are of equal length throughout the day. The latter are used today in the indication of the time exclusively.
Temporal time[edit]
For the display of temporal hours[1] almost exclusively the Sundial with Nodus as hand was used. The Sun position, which varied throughout the year, served as a parameter on which the varying length of the temporal hours during the year depended.
Many astronomical clocks, which were created during the transition to the equal-length equinoctial hours, still display the temporal hours in addition to the new equal-length hours.
Where temporal hours continued to be used for a long time (especially in monasteries), the new equally running mechanical clock accelerating the transition to the equal-length hours was permanently set faster/slower. 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 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. The two displays of the astronomical clocks are identical during this time.
See also[edit]
Bibliography[edit]
- 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.
External links[edit]
References[edit]
- ↑ Karlheinz Deußer: Temporaluhren: Die Suche nach mechanischen Uhren, die mit Temporalstunden liefen. 2012.
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