2. HOUR For the astronomical unit of measure of angle, see right ascension. For the newspaper, see The Hour (newspaper). The hour (common symbol h or hr) is a unit of time. It is not an SI unit but is accepted for use with the SI with the symbol h.
3. DEFINITION In modern usage, an hour is a unit of measurement of time of the duration of 60 minutes, or 3600 seconds. It is 1/24 of a median Earthday. An hour in the Universal Coordinated Time (UTC) time standard can include a negative or positive leap second, and may therefore have a duration of 3599 or 3601seconds for adjustment purposes.
4. Etymology Further information: horoscopy and Year#Etymology Middle Englishure first appears in the 13th century, as a loanword from Old Frenchure, ore, from Latin hora, ultimately from Greek ὥρα "season, time of day, hour". Middle English ure, Anglo-Frenchhoure replaced Old Englishtíd (which survives as Modern English tide) and stund (Old High Germanstunta, from a Germanic *stundō "time, interval, while"). Greek ὥρα is cognate to English year, both from a PIE*i̯ēro- "year, summer".