![]() ![]() 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). ![]()
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