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Unequal hours
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Unequal hours
Unequal hours are the division of the daytime and the nighttime into 12 sections each, whatever the season. They are also called temporal hours, seasonal hours, biblical or Jewish hours, as well as ancient or Roman hours (Latin: horae temporales). 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 by the now common ones of equal duration.
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.
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 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 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) every day in summer and rises every day in winter. Day does not occur.
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 (Ancient Greek: ὥραι καιρικαί, romanized: horai kairikai).
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Unequal hours
Unequal hours are the division of the daytime and the nighttime into 12 sections each, whatever the season. They are also called temporal hours, seasonal hours, biblical or Jewish hours, as well as ancient or Roman hours (Latin: horae temporales). 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 by the now common ones of equal duration.
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.
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 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 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) every day in summer and rises every day in winter. Day does not occur.
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 (Ancient Greek: ὥραι καιρικαί, romanized: horai kairikai).
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