Hour

The hour ( from Old High German stunta, Standing ',' stay ' ) is the twenty-fourth part of a day. In addition to a division into 24 equal parts, there are other terms hours.

The Latin word hora, so the unit symbol h or h

The unit hour

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

As today's atomic clocks, the time can be measured very accurately, and the rotational speed of the earth varies, the hour has been redefined over a second, which combines atomic time with astronomical universal time.

Hours counting and division

The 24 -hour count of an entire day is first attested in ancient Egypt and later found among others in Ancient Greece around the 3rd century BC application, where the 24 -hour system derived from the square. From there it spread even to the time of turning over all the (old ) world.

Throughout history, various methods for counting hours, so the numbering were used:

• In the ancient Egyptian hours counting the sunrise is considered the beginning of the first hour of the day; the sunset as the end of the twelfth hour of the day and the evening twilight as the first hour of the night and the dawn as the twelfth hour of the night
• In the Babylonian hours counting ( Greek hours) of the sunrise is considered the beginning of the first hour.
• The Italian hours counting ( also bohemian or Large clock ) for the first hour begins at sunset. Hours were counted 1-24. It is derived from the usual today Islamic calendar.
• In the modern 12-hour count ( Small clock, bourgeois hours) begins the hour counter at midnight and noon with 12, then is incremented from 1 to 11. The two half- days to 12 hours ante meridiem (AM, " before noon " ) and post meridiem ( pm, " after midday " ) called.
• In the modern 24 -hour count ( astronomical hours) starts counting the hours at midnight, the hours are counted from 0 to 23.
• When Julian Date astronomers the hours counting starts at noon.

As a full hour is defined as the start of the minute one, so for example, 8:00:00; it is also called " beat eight ". The term comes from the fact that (in the above example) " the eighth hour full". Derived from the popular hours subdivisions half hour, quarter hour, and the time information (chronological) " quarter to eight " ( 7:15 ), "half eight ' ( 07:30 ), " a quarter to eight "or" seven forty-five " (07: 45) and " quarter past eight " ( 8:15 ).

Other definitions of the length of the hour

The term ' hour ' is - near the present physico- term chronometric - also used for the historical chronological and astronomical time systems:

• Aequale hours: One hour length subject to its own definitions and is not bound to a 24- hour division.
• Temporal hours ( Roman hours): The diurnal arc of the clear day ( sunrise to sunset) was divided into twelve parts and correspondingly transferred to the night. Due to the different length of day and night during the year is also the hour lengths vary continuously.
• Seasonal Hours: Similar to the temporal hours of the day and the night into periods of varying duration is divided, but differs from a continuous 24 -hour division.
• Equinoctial hours: An equinoctial hour, the twenty-fourth part of the solar day and the seasonally changing day and night arc independent.