24 Hour Tag
Mara Ermogemous
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In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds. However, on rare occasions an hour may incorporate a positive or negative leap second,[a] effectively making it appear to last 3,599 or 3,601 seconds, in order to keep UTC within 0.9 seconds of UT1, the latter of which is based on measurements of the mean solar day.
The time of day is typically expressed in English in terms of hours. Whole hours on a 12-hour clock are expressed using the contracted phrase o'clock, from the older of the clock.[6] (10 am and 10 pm are both read as "ten o'clock".)
Fifteen and thirty minutes past the hour is expressed as "a quarter past" or "after"[8] and "half past", respectively, from their fraction of the hour. Fifteen minutes before the hour may be expressed as "a quarter to", "of", "till", or "before" the hour.[8] (9:45 may be read "nine forty-five" or "a quarter till ten".)
The ancient Greeks kept time differently than is done today. Instead of dividing the time between one midnight and the next into 24 equal hours, they divided the time from sunrise to sunset into 12 "seasonal hours" (their actual duration depending on season), and the time from sunset to the next sunrise again in 12 "seasonal hours".[9] Initially, only the day was divided into 12 seasonal hours and the night into three or four night watches.[10]
By the Hellenistic period the night was also divided into 12 hours.[11] The day-and-night (νυχθήμερον) was probably first divided into twenty-four hours by Hipparchus of Nicaea.[12] The Greek astronomer Andronicus of Cyrrhus oversaw the construction of a horologion called the Tower of the Winds in Athens during the first century BCE. This structure tracked a 24-hour day using both sundials and mechanical hour indicators.[13]
The canonical hours were inherited into early Christianity from Second Temple Judaism.By AD 60, the Didache recommends disciples to pray the Lord's Prayer three times a day; this practice found its way into the canonical hours as well. By the second and third centuries, such Church Fathers as Clement of Alexandria, Origen, and Tertullian wrote of the practice of Morning and Evening Prayer, and of the prayers at the third, sixth and ninth hours.In the early church, during the night before every feast, a vigil was kept. The word "Vigils", at first applied to the Night Office, comes from a Latin source, namely the Vigiliae or nocturnal watches or guards of the soldiers. The night from six o'clock in the evening to six o'clock in the morning was divided into four watches or vigils of three hours each, the first, the second, the third, and the fourth vigil.[14]
The Horae were originally personifications of seasonal aspects of nature, not of the time of day.The list of twelve Horae representing the twelve hours of the day is recorded only in Late Antiquity, by Nonnus.[15] The first and twelfth of the Horae were added to the original set of ten:
Medieval astronomers such as al-Biruni[17] and Sacrobosco,[18] divided the hour into 60 minutes, each of 60 seconds; this derives from Babylonian astronomy, where the corresponding terms[clarification needed] denoted the time required for the Sun's apparent motion through the ecliptic to describe one minute or second of arc, respectively. In present terms, the Babylonian degree of time was thus four minutes long, the "minute" of time was thus four seconds long and the "second" 1/15 of a second.[19][20])
In medieval Europe, the Roman hours continued to be marked on sundials but the more important units of time were the canonical hours of the Orthodox and Catholic Church. During daylight, these followed the pattern set by the three-hour bells of the Roman markets, which were succeeded by the bells of local churches. They rang prime at about 6 am, terce at about 9 am, sext at noon, nones at about 3 pm, and vespers at either 6 pm or sunset. Matins and lauds precede these irregularly in the morning hours; compline follows them irregularly before sleep; and the midnight office follows that. Vatican II ordered their reformation for the Catholic Church in 1963,[21] though they continue to be observed in the Orthodox churches.
When mechanical clocks began to be used to show hours of daylight or nighttime, their period needed to be changed every morning and evening (for example, by changing the length of their pendula). The use of 24 hours for the entire day meant hours varied much less and the clocks needed to be adjusted only a few times a month.
The minor irregularities of the apparent solar day were smoothed by measuring time using the mean solar day, using the Sun's movement along the celestial equator rather than along the ecliptic. The irregularities of this time system were so minor that most clocks reckoning such hours did not need adjustment. However, scientific measurements eventually became precise enough to note the effect of tidal deceleration of the Earth by the Moon, which gradually lengthens the Earth's days.
The metric system bases its measurements of time upon the second, defined since 1952 in terms of the Earth's rotation in AD 1900. Its hours are a secondary unit computed as precisely 3,600 seconds.[22] However, an hour of Coordinated Universal Time (UTC), used as the basis of most civil time, has lasted 3,601 seconds 27 times since 1972 in order to keep it within 0.9 seconds of universal time, which is based on measurements of the mean solar day at 0 longitude. The addition of these seconds accommodates the very gradual slowing of the rotation of the Earth.
In modern life, the ubiquity of clocks and other timekeeping devices means that segmentation of days according to their hours is commonplace. Most forms of employment, whether wage or salaried labour, involve compensation based upon measured or expected hours worked. The fight for an eight-hour day was a part of labour movements around the world. Informal rush hours and happy hours cover the times of day when commuting slows down due to congestion or alcoholic drinks being available at discounted prices. The hour record for the greatest distance travelled by a cyclist within the span of an hour is one of cycling's greatest honours.
Many different ways of counting the hours have been used. Because sunrise, sunset, and, to a lesser extent, noon, are the conspicuous points in the day, starting to count at these times was, for most people in most early societies, much easier than starting at midnight. However, with accurate clocks and modern astronomical equipment (and the telegraph or similar means to transfer a time signal in a split-second), this issue is much less relevant.
In ancient and medieval cultures, the counting of hours generally started with sunrise. Before the widespread use of artificial light, societies were more concerned with the division between night and day, and daily routines often began when light was sufficient.[23]
"Babylonian hours" divide the day and night into 24 equal hours, reckoned from the time of sunrise.[24] They are so named from the false belief of ancient authors that the Babylonians divided the day into 24 parts, beginning at sunrise. In fact, they divided the day into 12 parts (called kaspu or "double hours") or into 60 equal parts.[25]
Sunrise marked the beginning of the first hour, the middle of the day was at the end of the sixth hour and sunset at the end of the twelfth hour. This meant that the duration of hours varied with the season. In the Northern hemisphere, particularly in the more northerly latitudes, summer daytime hours were longer than winter daytime hours, each being one twelfth of the time between sunrise and sunset. These variable-length hours were variously known as temporal, unequal, or seasonal hours and were in use until the appearance of the mechanical clock, which furthered the adoption of equal length hours.[23]
This is also the system used in Jewish law and frequently called "Talmudic hour" (Sha'a Zemanit) in a variety of texts. The Talmudic hour is one twelfth of time elapsed from sunrise to sunset, day hours therefore being longer than night hours in the summer; in winter they reverse.
In so-called "Italian time", "Italian hours", or "old Czech time", the first hour started with the sunset Angelus bell (or at 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 know 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; it was officially abolished in 1755, or in some regions customary until the mid-19th century.[c][26]
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