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Topic: Coordinated Universal Time

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Universal time

Time zone

History of standard time in the United States

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Central European Time

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UTC

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International Atomic Time

Australian Eastern Standard Time

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Sidereal time

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	The Time
		More precisely, it is the time coordinate of a space-time coordinate system that is centered in space on the barycenter of the solar system, that is nonrotating with respect to distant galaxies, and that tends asymptotically to the proper time of an observer at rest with respect to the coordinate system.
		Geocentric Coordinate Time, or TCG, is the same as Barycentric Coordinate Time, except that it uses the Earth's center, rather than the barycenter of the solar system (and an “asymptotic” observer is one free from the gravitational field of the Earth rather than that of all the solar system).
		Coordinated Universal Time, or UTC is the official standard of time throughout the world, being the basis for legal time.
	www.madore.org /~david/misc/time.html (3957 words)

	Coordinated Universal Time - Wikipedia, the free encyclopedia
		Coordinated Universal Time (UTC) is a high-precision atomic time standard which approximately tracks Universal Time (UT).
		UTC is derived from International Atomic Time (TAI), which is a time scale tracking proper time on the surface of the Earth with no reference to the rotation of the Earth.
		However, it was widely desired to keep civil time synchronised with the Earth's rotation, and many uses of time signals (such as for navigation) relied on their closely matching Universal Time.
	en.wikipedia.org /wiki/Coordinated_Universal_Time (2832 words)

	Wikipedia: Coordinated Universal Time
		Coordinated Universal Time or UTC, the basis for civil time, differs by an integral number of seconds from atomic time and a fractional number of seconds from UT1.
		Time zones around the world are expressed as positive and negative offsets from UTC.
		International standard UTC time can only be determined to the highest precision after the fact, as atomic time is determined by the reconciliation of the observed differences between an ensemble of atomic clocks maintained by a number of national time bureaus.
	www.factbook.org /wikipedia/en/c/co/coordinated_universal_time.html (614 words)

	Reference for Coordinated Universal Time - Search.com
		UTC replaced Greenwich Mean Time on 1 January, 1972 as the basis for the main reference time scale or civil time in various regions.
		However, it was widely desired to keep civil time synchronised with the Earth's rotation, and many uses of time signals (such as for navigation) relied on their closely matching Universal Time.
		The resulting gradual shift of the sun's movements relative to civil time is analogous to the shift of seasons relative to the yearly calendar that results from the calendar year not precisely matching the tropical year length.
	domainhelp.search.com /reference/Coordinated_Universal_Time (3422 words)

	NationMaster - Encyclopedia: Coordinated Universal Time (Site not responding. Last check: )
		However, because Universal Time is synchronous with night and day, and more precise atomic-frequency standards drift away from this, UT is still used to produce a correction called leap seconds to atomic time to obtain a broadcast form of civil time that carries atomic frequency.
		Coordinated Universal Time or UTC, also sometimes referred to as "Zulu time" or Z, is an atomic realization of Universal Time (UT) or Greenwich Mean Time (GMT), the astronomical basis for civil time.
		UTC is a hybrid time scale: the rate of UTC is based on atomic frequency standards but the epoch of UTC is synchronized to remain close to astronomical UT.
	www.nationmaster.com /encyclopedia/Coordinated-Universal-Time (515 words)

	Coordinated Universal Time (Site not responding. Last check: )
		Coordinated Universal Time or UTC, also sometimes referred to as "Zulu time", the basis for civil time, differs by an integral number of second s from atomic time and a fractional number of seconds from UT1.
		Time zone s around the world are expressed as positive and negative offsets from UTC.
		International standard UTC time can only be determined to the highest precision after the fact, as atomic time is determined by the reconciliation of the observed differences between an ensemble of atomic clocks maintained by a number of national time bureau s.
	www.serebella.com /encyclopedia/article-Coordinated_Universal_Time.html (1204 words)

	Systems of Time
		Universal Time (UT) is counted from 0 hours at midnight, with unit of duration the mean solar day, defined to be as uniform as possible despite variations in the rotation of the Earth.
		Geocentric Coordinate Time (TCG) is a coordinate time having its spatial origin at the center of mass of the Earth.
		Sidereal Time, with unit of duration the period of the Earth's rotation with respect to a point nearly fixed with respect to the stars, is the hour angle of the vernal equinox.
	tycho.usno.navy.mil /systime.html (560 words)

	Astronomical Times
		Several important time scales still follow the rotation of the earth, most notably civil and sidereal time, but of these are now derived from atomic time through a combination of earth rotation theory and actual measurements of the earth's rotation and orientation.
		Sidereal time is the measure of the earth's rotation with respect to distant celestial objects.
		It might seem strange that UT1, a solar time, is determined by measuring the earth's rotation with respect to distant celestial objects, and GMST, a sidereal time, is derived from it.
	www.cv.nrao.edu /~rfisher/Ephemerides/times.html (2060 words)

	NASA - Time Zones and Universal Time
		Universal Time or UT is the precise measure of time used as the basis for all civil time-keeping.
		Universal Time is actually based on the mean sidereal time as measured in Greenwich, England.
		Time zones for countries around the world can be determined with a special Time Zone Map courtesy of the HM Nautical Almanac Office, Royal Greenwich Observatory.
	sunearth.gsfc.nasa.gov /eclipse/SEhelp/TimeZone.html (589 words)

	Coordinated Universal Time (UTC)
		Coordinated Universal Time is essentially the same as Greenwich Mean Time (GMT), also called "Zulu" (Z) time.
		The reason for using UTC is to avoid confusion with time zones; if the time of a weather report is given as 1630Z (read 16:30 Zulu or UTC), a person anywhere in the world can determine the local time of the report by adjusting the UTC time appropriately.
		Local time is determined by subtracting the number of hours our time zone differs from the time in England.
	www.oneonta.edu /academics/wxclub/utc.htm (310 words)

	Time Zones and "Z" Time
		GMT time is also referred to as "Z" or, phonetically, "Zulu" time, for the letter identifying that time zone centered on the Greenwich Prime Meridian (See the time zone labels along the top of the accompanying World Map of Time Zones).
		Civil time zones were initially instituted in the U.S. and Canada in the 1880's by the railroads to standardize time keeping.
		Time in the Z or UTC system is reckoned from the local standard time observed along the Greenwich Meridian.
	www.meteor.wisc.edu /~hopkins/aos100/z-time.htm (746 words)

	Definition: coordinated universal time
		Coordinated Universal Time (UTC): Time scale, based on the second (SI), as defined and recommended by the CCIR, and maintained by the Bureau International des Poids et Mesures (BIPM).
		Twice yearly, during the last minute of the day of June 30 and December 31, Universal Time, adjustments may be made to ensure that the accumulated difference between UTC and UT-1 will not exceed 0.9 s before the next scheduled adjustment.
		Historically, adjustments, when necessary, have usually consisted of adding an extra second to the UTC time scale in order to allow the rotation of the Earth to "catch up." Therefore, the last minute of the UTC time scale, on the day when an adjustment is made, will have 59 or 61 seconds.
	www.its.bldrdoc.gov /fs-1037/dir-009/_1277.htm (257 words)

	Coordinated Universal Time (UTC) (Site not responding. Last check: )
		UTC is the time scale that is used worldwide to coordinate technical and scientific activities.
		It is a compromise between the highly stable atomic time and the irregular earth rotation.
		Universal Time UT1 is the time of the earth clock, which performs one revolution in about 24h.It has short term instabilities at the level of 10
	www.iers.org /iers/earth/rotation/utc/utc.html (288 words)

	Time and Frequency from A to Z
		A characterization is often used to determine the types of noise that limit the uncertainty of the measurement, and the sensitivity of the device to environmental changes.
		A clock consists of at least three parts: an oscillator, a device that counts the oscillations and converts them to units of time interval (such as seconds, minutes, hours, and days), and a means of displaying or recording the results.
		Cycle slips introduce phase shifts equal (in time units) to the period of the carrier frequency, or to a multiple of its period.
	tf.nist.gov /general/enc-ch.htm (701 words)

	Universal Time
		Times given in UT are almost always given in terms of a 24-hour clock.
		Sometimes a Z is appended to a time to indicate UT, as in 0935Z.
		Times which may be labeled "Universal Time" or "UT" in data provided by the Astronomical Applications Department of the U.S. Naval Observatory (for example, in the annual almanacs) conform to this definition.
	aa.usno.navy.mil /faq/docs/UT.php (691 words)

	Coordinated Universal Time (Site not responding. Last check: )
		Coordinated Universal Time (UTC) is the international time standard.
		Universal time is based on a 24 hour clock, therefore, afternoon hours such as 4 pm UTC are expressed as 16:00 UTC (sixteen hours, zero minutes).
		Counting the bands may not give you an exact time for your location, as countries impose their own time regions due to geographic borders, but it should be close.
	www.pcxt-micro.com /print/cutime-prn.html (233 words)

	The mktime function fails for January 1, 1970 in several time zones that are ahead of Coordinated Universal Time
		For time zones that are ahead of Coordinated Universal Time (Greenwich Mean Time), if you call the mktime function with the argument set to correspond to January 1, 1970 00:00:00 (midnight), mktime returns -1 (failure).
		Adjusted for current time zone means that the appropriate number of seconds will be added or subtracted so the mktime function actually returns the number of seconds that have elapsed since midnight January 1, 1970 Coordinated Universal Time.
		The return value of 28800 in the Pacific Time Zone means that 28,800 seconds have elapsed since January 1, 1970 00:00:00 Coordinated Universal Time when it is the same time in the Pacific Time Zone.
	support.microsoft.com /default.aspx?scid=kb%3ben-us%3b148790 (397 words)

	COORDINATED UNIVERSAL TIME UTC (Site not responding. Last check: )
		UTC is the time scale that is used worlwide to coordinate technical and scientific activities.
		Universal Time UT1,is the time of the Earth clock, which performs one revolution in about 24h.It has short term instabilities at the level of 10
		Because of the secular decelleration of the Earth's rotation, TAI, of which the unit of time, corresponds the second of the mean solar day of the epoch 1820, presents an continuous increasing (parabolic) shift with respect to UT1.
	hpiers.obspm.fr /eop-pc/earthor/utc/UTC.html (387 words)

	Coordinated Universal Time (UTC)
		Coordinated Universal Time (UTC), also referred to as Greenwich Mean Time (GMT), Universal Time (UT), or "Zulu" is an international time scale used in astronomical and aviation publications, weather products, and other documents.
		Time signals and voice announcements of the current UTC are also available from the U.S. Naval Observatory at (202) 762-1069 and (202) 762-1401.
		According to NIST, their telephone time announcements are normally delayed by less than 3/100 of a second when using land lines from within the continental United States and the delay variation is generally less than 1/1000 of a second.
	www.spacearchive.info /utc.htm (1363 words)

	The Ultimate Coordinated Universal Time - American History Information Guide and Reference
		Coordinated Universal Time or UTC, also sometimes referred to as "Zulu time", is an atomic realization of Universal Time or Greenwich mean time, the astronomical basis for civil time.
		Time zones around the world are expressed as positive and negative offsets from UT. UTC differs by an integral number of seconds from atomic time and a fractional number of seconds from UT1.
		The UT time zone is sometimes denoted by the letter Z since the equivalent nautical time zone (GMT) has been denoted by Z since about 1950, and by a "zone description" of zero hours since 1920.
	www.historymania.com /american_history/UTC (578 words)

	Date and Time Formats
		Times are expressed in local time, together with a time zone offset in hours and minutes.
		A time zone offset of "+hh:mm" indicates that the date/time uses a local time zone which is "hh" hours and "mm" minutes ahead of UTC.
		A time zone offset of "-hh:mm" indicates that the date/time uses a local time zone which is "hh" hours and "mm" minutes behind UTC.
	www.w3.org /TR/NOTE-datetime (692 words)

	NASA/MSFC/ESSD - Coordinated Universal Time
		Universal time is based on a 24 hour clock, therefore, afternoon hours such as 4 pm UTC are expressed as 16:00 UTC (sixteen hours, zero minutes).
		Counting the bands may not give you an exact time for your location, as countries impose their own time regions due to geographic borders, but it should be close.
		Subtract time in west longitudes (negative values), add time in east longitudes (positive values).
	www.ghcc.msfc.nasa.gov /utc.html (221 words)

	CalendarHome.com - Coordinated Universal Time - Calendar Encyclopedia
		Originally, the local time at the Royal Greenwich Observatory in Greenwich, England was chosen as standard at the 1884 International Meridian Conference, leading to the widespread use of Greenwich Mean Time in order to set local clocks.
		Therefore, telemetry from coordinated clocks at rest (with respect to the rotating Earth!) and on the geoid is used to provide UTC, when required, on locations such as spacecraft.
		One of the earliest verifications of the effects of this application of general relativity, at altitudes and speeds attainable by ordinary passenger aircraft in 1971 was the Hafele-Keating experiment.
	encyclopedia.calendarhome.com /Coordinated_Universal_Time.htm (1047 words)

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