# hour

Physical unit
Unit name hour
Unit symbol ${\ displaystyle \ mathrm {h}}$
Physical quantity (s) Time , span of time
Formula symbol ${\ displaystyle t; \, T; \; \, \ tau, \, \ mathrm {T}}$
dimension ${\ displaystyle {\ mathsf {T}}}$
system Approved for use with the SI
In SI units ${\ displaystyle \ mathrm {1 \, h = 3600 \; s}}$
Named after Old  high German stunta
Derived from Day

The hour (from Old High German  stunta 'standing', 'stay', 'fixed point in time', 'short period', 'hour') denotes the twenty-fourth part of a day . In addition to a division into 24 equal parts, there are also other hour terms.

The Latin word is hora , hence the symbol h or h.

For the exact differentiation of an hour (with 60 minutes) e.g. B. of a lesson (often 45 minutes) is also referred to as a hour .

## The unit of measurement is hour

The hour is a unit of time . The unit symbol is h (from Latin hora ). The hour does not belong to the International System of Units (SI), but is approved for use with the SI. This makes it a legal unit of measurement . Due to the non- decimal subdivision, a conversion into seconds is first necessary for scientific calculations.

1 hour = 60 minutes = 3600 ( SI ) seconds

Since today's atomic clocks can measure time very precisely and the rotation speed of the earth varies, the hour was redefined as a second, which connects atomic time with universal astronomical time .

## Counting and dividing hours

The 24-hour counting of a whole day is first attested in ancient Egypt and was later used in ancient Greece around the third century BC, where the 24-hour system was derived from the angle . From there it spread over the whole (old) world until the turn of the times .

Various methods of counting hours, i.e. numbering , have been used throughout history :

The beginning of minute one is called the full hour , for example 08:00:00; it is also called "stroke eight". The term comes from the fact that (in the example above) “the eighth hour is full”. The widespread hour divisions of half an hour , quarter of an hour and the times (chronologically) "quarter eight" (07:15), "half eight" (07:30), "quarter to eight" or "quarter to eight" (07: 45) and "quarter past eight" (08:15).

## Other definitions of the length of the hour

Foldable pocket calendar (approx. 1400; SBB-PK, Lib. Pic. A 72) - complete monthly cycle with signs of the zodiac and list of hours with daylight per month.

The term 'hour' - in addition to today's physical-chronometric term - is also used for the historical chronological and astronomical time systems :

• Equal hours : An hour length is subject to its own definitions and is not tied to a 24-hour division.
• Temporal hours (Roman hours) : The day arc of the bright day ( sunrise to sunset) was divided into twelve parts and transferred accordingly to the night. Due to the different lengths of day and night in the course of the year, the length of the hours (between 30 and 90 minutes) also change continuously.
• In the horae canonicae , the first hour of the day ( prime ) began between 3 a.m. and 9:30 a.m. and the first hour of the night between 3 p.m. and 9:30 p.m. The English term afternoon refers to the 9th hour ( ninth ), which has been striking at 12 noon since around 1300.
• Seasonal hours : Similar to the temporal hours, the day and night are divided into periods of fluctuating duration, but deviate from a continuous 24-hour division.
• Equinox hour : An equinox hour is the twenty-fourth part of the sunny day and is independent of the day and night arcs that change with the seasons.