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Topic: Terrestrial Dynamical Time

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	Terrestrial Time - Wikipedia, the free encyclopedia
		Terrestrial Time (TT) is the modern time scale that is used instead of ephemeris time, which is obsolete.
		TT was introduced by the International Astronomical Union (IAU) in 1991 as the coordinate time scale consistent with the theory of relativity for an observer on the surface of the Earth.
		TDT was defined in 1976 by the IAU to be the counterpart of Barycentric Dynamical Time (TDB) as measured by clocks ticking SI seconds on the surface of the earth.
	en.wikipedia.org /wiki/Terrestrial_Dynamical_Time (367 words)

	Terrestrial Time -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-18)
		Terrestrial Time (TT) is the modern (An arrangement of events used as a measure of duration) time scale that is used instead of ((astronomy) a measure of time defined by Earth's orbital motion; terrestrial time is mean solar time corrected for the irregularities of the Earth's motions) ephemeris time, which is obsolete.
		TDT was defined in 1976 by the IAU to be the counterpart of (additional info and facts about Barycentric Dynamical Time) Barycentric Dynamical Time (TDB) as measured by clocks ticking SI seconds on the surface of the earth.
		Subsequently the IAU decided that the name of TDT was a misnomer because it did not correspond directly to anything dynamical in the theories of motion for bodies in the (The sun with the celestial bodies that revolve around it in its gravitational field) solar system.
	www.absoluteastronomy.com /encyclopedia/t/te/terrestrial_time.htm (448 words)

	Ephemeris time - Wikipedia, the free encyclopedia
		Ephemeris Time (ET) is a now obsolete time scale used in ephemerides of celestial bodies, in particular the Sun (as observed from the Earth), Moon, planets, and other members of the solar system.
		ET was replaced with the two time scales Terrestrial Dynamical Time (TDT) and Barycentric Dynamical Time (TDB) by the International Astronomical Union (IAU) in 1976—TDT was renamed Terrestrial Time (TT) in 1991.
		As the theoretical basis for Ephemeris Time is wholly non-relativistic, in 1976 the IAU resolved that beginning in 1984 ET would be replaced by the two relativistic timescales Barycentric Dynamical Time (TDB) and Terrestrial Dynamical Time (TDT).
	en.wikipedia.org /wiki/Ephemeris_Time (450 words)

	AllRefer.com - ephemeris time (Astronomy, General) - Encyclopedia
		ephemeris time (ET), astronomical time defined by the orbital motions of the earth, moon, and planets.
		Ephemeris time is calculated from the positions of the sun and moon relative to the earth, assuming that Newton's laws are perfectly obeyed.
		In 1984 ephemeris time was renamed terrestrial dynamical time (TDT or TT); also created was barycentric dynamical time (TDB), which is based on the orbital motion of the sun, moon, and planets.
	reference.allrefer.com /encyclopedia/E/ephemeri-t.html (266 words)

	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).
		Terrestrial Time, or TT (sometime called Terrestrial Dynamical Time, TDT), is, as its name indicates, the time scale on Earth.
	www.madore.org /~david/misc/time.html (3957 words)

	Systems of Time (Site not responding. Last check: 2007-10-18)
		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.
		Terrestrial Time (TT), (or Terrestrial Dynamical Time, TDT), with unit of duration 86400 SI seconds on the geoid, is the independent argument of apparent geocentric ephemerides.
		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)

	SOI-TN-94-116: Time Data Type & Representation
		The expression of dates and times externally is complicated by the dual aims of supporting a broad variety of "natural" representations and of being able to use multiple time scales.
		TDT differs from TAI by a variable amount, but for times of interest the difference is within 10 usec of its exact value at the 1977.0 TAI epoch of 32.184 sec = 0.0003725 day.
		The default is that Terrestrial Time (TT or TDT) is assumed.
	soi.stanford.edu /general/TechNotes/94.116.html (1883 words)

	4.2 Time
		The apparent (mean) sidereal time is used for astronomical observation and the mean sidereal time is used to construct a time scale: the Mean Sidereal Day (a difference of 0.0084 seconds with the Earth revolution period due to the precesion).
		The Dynamical Time corresponds to the concept of the inertial time, i.e.
		Terrestrial Dynamical Time (TDT) is referred to the geocenter (Proper Time with periodic variations up to 1.6 milliseconds, but common between satellite and Earth).
	maite152.upc.es /~manuel/tdgps/node18.html (645 words)

	Astronomical Time Keeping
		Moreover, siderial time is one of the constituents of Universal Time.
		Since the time reading at the Sun's passage through the meridian should be 12 h, though, the true solar time comes out as the hour angle of the anti-sun (which is the fictitious point on the ecliptic opposite to the Sun).
		The Ephemeris Time (ET) was consequently defined as the timescale that together with the laws of motion correctly predicts the positions of celestial bodies, and it is therefore used as the argument in the ephemerides.
	www.maa.mhn.de /Scholar/times.html (4032 words)

	Multiple Time Display Converter
		Loran time was zero at 0h 1-Jan-1958 and since it is not affected or altered by leap seconds it is now ahead of UTC by TAI, Temps Atomique International, is the international atomic time scale based on a continuous counting of the SI second.
		TDT is independent of the variable rotation of the Earth, and the lengths of the tropical year and synodic month are generally defined in days of 86,400 seconds of international atomic time.
		TDT is used as the time scale of ephemerides for observations from Earth's surface, and differs from international atomic time (TAI) by an offset of 32.184 seconds (TDT=TAI + 32.184), which varies slightly with time.
	www.csgnetwork.com /multitimedisp.html (399 words)

	Systems of Time
		With atomic time the unit of a second is defined as; the duration of 9,192,631,770 cycles of microwave light absorbed or emitted by the hyperfine transition of cesium-133 atoms in their ground state undisturbed by external fields.
		Sometimes represented as (TT), or Terrestrial Dynamical Time, (TDT), with unit of duration 86400 SI seconds on the geoid, It was defined as being equal to TAI (Atomic time) plus 32.184 (atomic) seconds at the instant beginning 1 January 1977.
		Closely connected with the Mean Solar Time is the Sidereal Time, which is defined as the RA (Right Ascension) of the Local Meridian: when the Vernal Point passes the meridian it is 00:00 Sidereal Time.
	www.extremescience.com /time-systems.htm (844 words)

	Time Routines in CSPICE
		Atomic time is based upon the atomic second as defined by the ``oscillation of the undisturbed cesium atom.'' Atomic time is simply a count of atomic seconds that have occurred since the astronomically determined instant of midnight January 1, 1958 00:00:00 at the Royal Observatory in Greenwich, England.
		Ephemeris time is the uniform time scale represented by the independent variable in the differential equations that describe the motions of the planets, sun and moon.
		A comparison of the times kept by a clock at the solar system barycenter with a TDB clock on earth would reveal that the two clocks are in close agreement but that they run at different rates at different times of the year.
	www.gps.caltech.edu /~marsdata/req/time.html (11669 words)

	NASA - Delta T (Site not responding. Last check: 2007-10-18)
		For many centuries, the fundamental unit of time was the rotational period of the Earth with respect to the Sun.
		Unfortunately, Universal Time is not a uniform time scale because Earth's rotational period is gradually decreasing.
		Although solar eclipse predictions are based on Terrestrial Dynamical Time, the position of the central eclipse path still depends on Universal Time.
	sunearth.gsfc.nasa.gov /eclipse/SEhelp/deltaT.html (908 words)

	Barycentric Dynamical Time - Art History Online Reference and Guide
		Barycentric Dynamical Time (TDB) was defined by the International Astronomical Union (IAU) in 1976 to be used as the relativistic replacement for the non-relativistic Ephemeris Time which had been used in the ephemerides starting in 1960.
		Terrestrial Dynamical Time (TDT) and TDB were defined in a series of resolutions at the same meeting of the International Astronomical Union.
		Despite IAU recommendations that TCB be used for all further calculations of solar system ephemerides, as of 2002 TDB and Ephemeris Time continue to be used, the latter by the producer of the important DE200 ephemeris and its successors at the Jet Propulsion Laboratory.
	www.arthistoryclub.com /art_history/TDB (651 words)

	Calendars
		Historically, the calculation of time has been based on the position of the earth relative to the sun using noon, when the sun is highest in the sky, as a marker.
		The length of the second, which corresponds to the length of time required for 9,192,631,770 cycles of the Cesium atom at zero magnetic field, was determined near the end of the 19th century; this second is thus equivalent to the second defined by the fraction 1/31 556 925.97 47 of the year 1900.
		World time is typically adjusted every year by adding what is called a “leap second.” Because the time calculated by the position of the sun differs from the time calculated by the atomic standard, it is occasionally necessary to adjust international time standards to match the position of the Earth.
	www.calendarspro.com /blog (9836 words)

	Terrestrial Time at opensource encyclopedia (Site not responding. Last check: 2007-10-18)
		Terrestrial Time (TT) is the modern time scale that is used instead...
		terrestrial dynamical time (TDT): dynamical time for geocentric phenomena...
		Terrestrial Dynamical Time (TDT) is dynamical time for geocentric phenomena which replaced Ephemeris Time when the IAU 1976 System of Astronomical Constants was implemented in the Astronomical Almanac in 1984.
	www.springknow.com /TT.html (848 words)

	Keeping Time on Windows Machines
		Dynamical time for barycentric phenomena (TDB) used as a time scale of ephemerides, referred to as the barycenter — the center of mass (a common axis of rotation) around which the solar system revolves.
		Terrestrial Dynamical Time (TDT) for geocentric phenomena — which is independent of the variable rotation of the Earth —; is used as the time scale of ephemerides (daily table showing planetary positions) for observations from Earth's surface.
		TDT differs from "TAI" an abbreviation due to a compromise between French and English for "International Atomic Time") which measures the International System SI second as the time required for 9,192,631,770 vibrations (transition cycles) of a Cesium (Cs-133) atom in a Cs clock.
	www.wilsonmar.com /1clocks.htm (2826 words)

	Stellafane Moon Phase Calculator (Site not responding. Last check: 2007-10-18)
		TIME ACCURACY: The calculated times are in Terrestrial Dynamical Time (TDT or TT), a replacement for Ephemeris Times (ET).
		Civil time, such as UTC (popularly known as GMT, but technically incorrect) or your local time, is corrected for the non-linear changes in the rotation of the earth.
		If the local time is in the wrong time zone for you, you need to check and adjust these settings on your computer, there is nothing in this web page or the code behind it to change this.
	www.stellafane.com /moon_phase/moon_phase.htm (498 words)

	[sci.astro] Time (Astronomy Frequently Asked Questions) (3/9) (Site not responding. Last check: 2007-10-18)
		SIDEREAL TIME: Closely connected with the Mean Solar Time is the Sidereal Time, which is defined as the RA (Right Ascension) of the Local Meridian: when the Vernal Point passes the meridian it is 00:00 Sidereal Time.
		At first the time to be used within a country was the local time of the capital of the country.
		There are two kinds of Dynamical Time: TDT (Terrestrial Dynamical Time), which is a time scale tied to the Earth, and TDB (Barycentric Dynamical Time), used as a time reference for the barycenter of the solar system.
	www.faqs.org /faqs/astronomy/faq/part3 (7327 words)

	Sky Publishing - Time and the Amateur Astronomer (Site not responding. Last check: 2007-10-18)
		To a person watching the sky 13 miles west of you, the time seems to be 11:59 when you swear it's 12:00 and someone 13 miles east insists it's 12:01.
		Logically enough, the "universal" time zone that was agreed upon is that of 0° longitude.
		In 1984 ET was renamed Terrestrial Dynamical Time (TDT or TT); also created was Barycentric Dynamical Time (TDB), which is referred to the solar system's center of mass.
	www.wwnorton.com /astro21/sandt/time.html (1759 words)

	Calendars and their History
		The generality of this definition is due to the diversity of methods that have been used in creating calendars.
		At that time the patriarch Hillel II, breaking with tradition, disseminated rules for calculating the calendar.
		The Julian proleptic calendar is formed by applying the rules of the Julian calendar to times before Caesar's reform.
	astro.nmsu.edu /~lhuber/leaphist.html (8496 words)

	[No title]
		An interim solution was to use a specific "railway time," but soon standard time zones were created.
		Colloquially the term "blue moon" is used to mean "a very long time." In fact, there have been at least seven different uses of the term "blue moon" in the past several hundred years.
		This phenomenon is called the "equation of time." This is just a fancy name for the fact that the Sun's speed along the Earth's equator is not constant.
	sciastro.astronomy.net /sci.astro.3.FAQ (6903 words)

	ephemeris time
		By convention, the standard seasonal year is taken to be A.D. 1900 and to contain 31,556,925.9747 sec of ephemeris time.
		The GOES time code service, 1974-2004: a retrospective.(Geostationary Operational Environmental Satellites) (Journal of Research of the National Institute of Standards and Technology)
		Atmel and u-blox Introduce Innovative New 'Aiding' Functionality to Antaris GPS Receiver to Speed Up Time to First Fix in Under Four Seconds; Users Will Experience Dramatic Improvement in Time to First Fix at No Additional Cost.
	www.infoplease.com /ce6/sci/A0817460.html (293 words)

	terrestrial time (HyperDic hyper-dictionary)
		TERRESTRIAL TIME products: USA, UK, Canada, Deutschland, France.
		(astronomy) a measure of time defined by Earth's orbital motion.
		Terrestrial time is mean solar time corrected for the irregularities of the Earth's motions.
	www.hyperdic.net /dic/terrestrial_time.htm (89 words)

	TT (disambiguation) - Freepedia (Site not responding. Last check: 2007-10-18)
		The Transport Tycoon computer game by Chris Sawyer
		Time Team, a popular archaeological British TV program on Channel 4
		This page was last modified 17:10, 11 November 2005.
	en.freepedia.org /Tt.html (121 words)

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