In the early church, during the night before every feast, a vigil was kept. 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. The canonical hours were introduced to early Christianity from Second Temple Judaism.īy 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. This structure tracked a 24-hour day using both sundials and mechanical hour indicators. 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. The day-and-night ( νυχθήμερον) was probably first divided into twenty-four hours by Hipparchus of Nicaea. īy the Hellenistic period the night was also divided into 12 hours. Initially, only the day was divided into 12 seasonal hours and the night into three or four night watches. 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'. The ancient Greeks kept time differently than is done today. (9:45 may be read 'nine forty-five' or 'a quarter till ten'.) Fifteen minutes before the hour may be expressed as 'a quarter to', 'of', 'till', or 'before' the hour. (1000 is read 'ten hundred' or 'ten hundred hours' 10 pm would be 'twenty-two hundred'.)įifteen and thirty minutes past the hour is expressed as 'a quarter past' or 'after' and 'half past', respectively, from their fraction of the hour.

Hours on a 24-hour clock ('military time') are expressed as 'hundred' or 'hundred hours'. (10 am and 10 pm are both read as 'ten o'clock'.) Whole hours on a 12-hour clock are expressed using the contracted phrase o'clock, from the older of the clock. The time of day is typically expressed in English in terms of hours. Its Proto-Indo-European root has been reconstructed as *yeh₁- ('year, summer'), making hour distantly cognate with year. Like Old English tīd and stund, hṓrā was originally a vaguer word for any span of time, including seasons and years. The Anglo-Norman term was a borrowing of Old French ure, a variant of ore, which derived from Latin hōra and Greek hṓrā ( ὥρα). It displaced tide tīd, 'time' and stound stund, span of time. Hour is a development of the Anglo-Norman houre and Middle English ure, first attested in the 13th century. However, on rare occasions an hour may incorporate a positive or negative leap second, 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. In the modern metric system, hours are an accepted unit of time defined as 3,600 atomic seconds. Since this unit was not constant due to long term variations in the Earth's rotation, the hour was finally separated from the Earth's rotation and defined in terms of the atomic or physical second.

Such seasonal hours, also known as temporal hours or unequal hours, varied by season and latitude.Įqual hours or equinoctial hours were taken as 1⁄ 24 of the day as measured from noon to noon the minor seasonal variations of this unit were eventually smoothed by making it 1⁄ 24 of the mean solar day. The hour was initially established in the ancient Near East as a variable measure of 1⁄ 12 of the night or daytime. There are 60 minutes in an hour, and 24 hours in a day. on a 24-hour clock with a digital faceĪn hour ( symbol: h also abbreviated hr) is a unit of time historically reckoned as 1⁄ 24 of a day and defined contemporarily as exactly 3,600 seconds ( SI). Midnight (or noon) to 1 on a 12-hour clock with an analogue face Midnight to 1 a.m. For other uses, see Hour (disambiguation).

Set timer 1 hour 35 minutes