Civil time is another name for mean solar time reckoned from midnight. Some astronomical and navigational timekeeping conventions in use before the mid-20th century reckoned the beginning of the mean solar day at noon. At one time Greenwich mean time (GMT) could refer to either convention, so the International Astronomical Union introduced the term Universal Time to suggest GMT with the civil day beginning at midnight. Solar time is based on the idea that, when the sun reaches its highest point in the sky, it is noon. ... Midnight, literally the middle of the night, was a time arbitrarily designated to determine the end of a day and the beginning of the next in some, mainly Western, cultures. ... Solar time is based on the idea that, when the sun reaches its highest point in the sky, it is noon. ... For alternate meanings of GMT, see GMT (disambiguation). ... The International Astronomical Union (IAU) unites national astronomical societies from around the world. ... Universal Time (UT) is a timescale based on the rotation of the Earth. ...
Civil time has precise astronomical meaning. However, more recently this term is sometimes found with reference to specific statutory or standard time scales designated by civilian authorities, or with reference to local or standard time indicated by clocks. Generally speaking, the non-astronomical uses of this label are considered imprecise.
Civiltime may be formally defined as mean solar time plus 12 hr; the civil day begins at midnight, while the mean solar day begins at noon.
Civiltime is occasionally adjusted by one-second increments to ensure that the difference between a uniform timescale defined by atomic clocks does not differ from the earth's rotational time by more than 0.9 seconds.
Civiltime is usually not used, since it depends on the observer's longitude; instead, standard time, which is the same throughout a given time zone, is generally adopted.
Uniform time scales, such as International Atomic Time (TAI) and Terrestrial Time (TT), are also historically based on GMT, but are not kept synchronized with the earth's rotation, and thus increasingly diverge from UT. Many representations of decimal time, such as Modified Julian Dates and astronomical calendar dates, use UT or uniform time scales.
French decimal time used local true, or apparent, solar time, that is, 5 o'clock on a decimal clock occurred exactly at true noon, when the sun reached its highest point in the sky at the location of the observer, and 10 o'clock was at true midnight, midway between two successive high points.
Alternately, one time of day might be used everywhere, and individuals and organizations could choose to adjust their own schedules according to when the sun shines in their part of the world, without changing the time of day.
Share your thoughts, questions and commentary here
Want to know more? Search encyclopedia, statistics and forums:
Press Releases |
The Wikipedia article included on this page is licensed under the
Images may be subject to relevant owners' copyright.
All other elements are (c) copyright NationMaster.com 2003-5. All Rights Reserved.
Usage implies agreement with terms, 1022, m