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Topic: Terrestrial Time

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  Terrestrial Time - Wikipedia, the free encyclopedia
Terrestrial Time (TT) is the modern time standard for time on the surface of the Earth.
In astronomy it is used as the time coordinate for apparent ephemerides for an Earthbound viewer.
TT is a Platonic time scale: a theoretical ideal, not dependent on a particular realisation.
en.wikipedia.org /wiki/Terrestrial_Time   (886 words)

 Time standard - Wikipedia, the free encyclopedia
A time standard is a specification or standard of either the rate at which time passes, or points in time, or both.
Solar time is based on the solar day, which is the period of time between one solar noon and the next.
Terrestrial Time is time at the surface of the Earth.
en.wikipedia.org /wiki/Time_standard   (1242 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)

 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.
Terrestrial Dynamic Time, which is tied to atomic time by a constant offset of 32.184 seconds, replaced ET at the beginning of 1984.
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)

 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.
The default is that Terrestrial Time (TT or TDT) is assumed.
The clock time is expressed in the customary colon-separated fields, with an optional decimal point and fractional part of a second.
soi.stanford.edu /general/TechNotes/94.116.html   (1883 words)

 Systems of Time   (Site not responding. Last check: 2007-11-06)
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)

 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).
Both kinds of time, based on the rotation of the Earth, differs basically due to the different reference: mean vernal equinox (Aries point) for sidereal time and mean Sun for universal 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)

 "Amateur Astronomy". Time Systems   (Site not responding. Last check: 2007-11-06)
Technically the sidereal time is referring to the vernal equinox as, due to the motion of the Earth on its orbit, a same star may not be observed at night all year long.
The "Universal Time" (UT) is an astronomical time.
Terrestrial Time (TT) or Terrestrial Dynamical Time (TDT) is the base for geocentric ephemeris predictions as Barycentric Dynamical Time (TDB) is used for predictions referring to the solar system barycenter (the solar system center of gravity).
stars5.netfirms.com /times.htm   (1349 words)

 [No title]   (Site not responding. Last check: 2007-11-06)
The measurement of times, the measurement of speeds, the measurement of dimensions of a moving body, relatively to a referential, require precise definitions.
This time is used to date astronomical events, and serves as reference to the calculation of times given by time zones.
On the equator, times are measured by sundials, which give local times, or by the universal time given by the sundial of the Greenwich meridian, universal time being sent by radio for example.
members.aol.com /sergecabala/TimeZones.htm   (2781 words)

 [No title]
Representation of Dates and Times\ \ 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.
It is best when referring to both future times and times in the distant past to use dynamical or atomic time.\ \ Two alternative forms are available for full specification of a time.
If zone time is used, no check for agreement with civil time is implied; the date-time 1995.07.27_12:00:00_MST is valid and refers to the same instant regardless of whether the event referred to (if any) occurs in Colorado, Arizona, or Sonora.
soi.stanford.edu /technotes/94.116.rtf   (1532 words)

 Astrobiology Magazine
Once synchronized to the time appropriate to a particular longitude on Mars, such a watch would give an approximate trace of the Sun's position in the sky so that 12 noon, for example, would provide a rough indication of the time it could be expected to cross the overhead meridian.
The discrepancy is referred to as the "equation of time," as needed for the accurate interpretation of a sundial measurement.
But the standardization of world-wide time zones and their reference to a "prime meridian" was realized only as recently as 1884, largely as result of the tireless persuasion of Sir Sanford Fleming, a Canadian railroad engineer.
www.astrobio.net /news/print.php?sid=826   (2739 words)

 D Suggested Time Scale Specification
Terrestrial Time, the IAU standard time scale since 1984; continuous with ET and synchronous with (but 32.184 s ahead of) TAI.
By default, times will be deemed to be as measured at the detector (or in practical cases, at the observatory) for times that run synchronously with TAI (i.e., TAI, UTC, and TT).
In the case of coordinate times (such as TCG and TCB) and TDB which are tied to an unambiguous coordinate origin, the default meaning of time values will be: time as if the observation had taken place at the origin of the coordinate time system.
archive.stsci.edu /fits/fits_standard/node87.html   (537 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)

 CEN 511: The Times of Your Lives   (Site not responding. Last check: 2007-11-06)
Time is an important quantity to measure, even if quantum physicists and philosophers don't know what it is. If you think it's as simple as knowing when to set your watch back to standard time, then you have some learning to do.
Civil time consists of 24 time zones, each 15 degrees wide, centered on lines of longitude which are multiples of 15 degrees (there are local variations).
Universal Time: This is the zero-point of civil time.
www.ess.sunysb.edu /fwalter/AST101/time.html   (835 words)

 Terrestrial Time -   (Site not responding. Last check: 2007-11-06)
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.
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 solar system.
psychcentral.com /psypsych/Terrestrial_Time   (408 words)

 SCAR » Appendix 7
The terrestrial record of late Phanerozoic (the last 100 m.y., or Late Cretaceous-Cenozoic) Antarctica is the most poorly understood of all major continental landmasses, even after forty years of intensive investigation since the International Geophysical Year (1957-58).
Terrestrial successions from the tectonically stable continental interior will be more difficult to date by conventional methods.
Current terrestrial data bases provide a wealth of information on the paleobotanical record for West and East Antarctica, but the invertebate and vertebrate paleozoological record is surprisingly meager.
www.scar.org /publications/reports/16/appendix7/webb2.html   (1837 words)

 GEOL 105 Sample Lesson - History of the Earth
Predicting accurately the time of eruption of a volcano or occurrence of a major earthquake might save lives and property, and, of course, it would have much greater social and economic impact than merely describing the horror of yesterday's volcanic eruption or earthquake.
In fact, imparting an appreciation of the immensity of geological time and of the great age of the earth is one principal objective of this course and the primary contribution of geology to the intellectual development of Western civilization.
In their time, the concepts advanced by the founders of geology, which now seem so straightforward, were equally difficult to grasp.
www.kuce.org /isc/previews/geol/geol105_lesson.html   (2922 words)

 [sci.astro] Time (Astronomy Frequently Asked Questions) (3/9)
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.
The amount of refraction is proportional to the path length through the atmosphere times the density gradient (in a linear approximation for the atmosphere's index of refraction).
www.faqs.org /faqs/astronomy/faq/part3   (7327 words)

 Technical Notes on Mars Solar Time   (Site not responding. Last check: 2007-11-06)
Time tags for the Mars Pathfinder Lander were referenced with respect to the local true solar time, with elapsed sols reckoned from the local true solar midnight preceding its landing, but designated with a starting number "1" rather than zero.
The derivation of mission time adopted by the Mars Exploration Rover Project by mission controllers at the NASA Jet Propulsion Laboratory is an offset modification of an evenly advancing mean solar time, based on its definition by Roncoli et al.
August 2003: The conversion between the terrestrial time TT and Universal Coordinated Time UTC as given by Equation 27 of AM2000 was modified for greater accuracy with a fourth-order polynomial representation, accurate to within 3 s for 1975-2005.
www.giss.nasa.gov /tools/mars24/help/notes.html   (2489 words)

 RXTE Absolute Timing Accuracy
To properly understand the various elements involved in establishing absolute time, one has to be aware of the different components and time systems.
In event modes, individual time bins are enumerated, each with an implied event count of 1 and a width equal to the time resolution.
The keyword TIMEPIXR indicates the relative position of the time stamp in the bins: a value of 0.0 indicates that the time stamp refers to the beginning of the bin; 0.5 the center of the bin; 1.0 the end of the bin.
heasarc.gsfc.nasa.gov /docs/xte/abc/time.html   (1014 words)

 Time Resources
The time notation described here is already the de-facto standard in almost all countries and the date notation is becoming increasingly popular, especially in computer applications.
These systems are based on the travel time of the electromagnetic signals: an accuracy of 10 nanoseconds (10 one billionths of a second) corresponds to a position accuracy of 10 feet.
Systems of time Atomic time, with the unit of duration the Systeme International (SI) second defined as the duration of 9,192,631,770 cycles of radiation corresponding to the transition between two hyperfine levels of the ground state of cesium 133.
www.edu-observatory.org /gps/time.html   (699 words)

 Terrestrial Time
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 general relativity for an observer on the surface of the Earth.
For all practical purposes, it is equal to:
www.ebroadcast.com.au /lookup/encyclopedia/tt/TT.html   (58 words)

 PHY 445/515: The Times of your Life   (Site not responding. Last check: 2007-11-06)
The UT times (based on the terrestrial rotation), with a day of length 86400 seconds (by definition), are kept in line with the occasional addition of leap seconds.
Sidereal Time is based on the Earth's sidereal rotation period (rotation with respect to the stars).
GAST (Greenwich Apparent Sidereal Time) = GMST + the equation of the equinoxes.
www.ess.sunysb.edu /fwalter/AST443/times.html   (1207 words)

 The ABC of XTE: A Time Tutorial
The time stamps presented by RXTE FITS tables as generated by XFF are in TT.
See the Timing Digest for a figure of fine clock corrections as a function of time.
The maximum attainable absolute time precision, using the tdc.dat file corrections, is between 5 and 8 microseconds.
heasarc.gsfc.nasa.gov /docs/xte/abc/time_tutorial.html   (1045 words)

 Decimal Time - Decimal Dates
The fractional day for Julian Dates is 0.0 at 12:00 Universal Time and 0.5 at 00:00 UT. Julian Ephemeris Dates (JED) are the same as Julian Dates but always start 0.0 at 12h Terrestrial Time (TT) for recent dates and 12h Ephemeris Time (ET) for older dates.
The siderial year is the time it takes the earth to revolve once around the sun, relative to other stars, or 365.256366 days.
The anomalistic year is the time it takes the earth to make two successsive passages through the perihelion, or 365.259636 days.
www.decimaltime.hynes.net /dates.html   (2027 words)

 My time against yours   (Site not responding. Last check: 2007-11-06)
In the example of Jonathon Keats, a ‘Keats second’; is equal to 0.909 of a terrestrial second, and therefore one terrestrial second measures 1.100 ‘Keats seconds’;.
Whoever can dictate the time is the one who reigns: the Church, with its bells that regulate life, then the King, and finally the State.
The progress of synchronizing the time (the ‘same time’ for all) has thus accompanied the gradual rise of democracy, the most ‘advanced’ and ‘synchronized’ form of social organization. /europastar/headlines/article_display.jsp?vnu_content_id=1002274749   (554 words)

 Artemis Project: Terrestrial Time Zones used by Lunar Crews
They have enough to think about without having to calculate time zone changes in their head.
The time tags are even corrected to Ground Elapsed Time.
Back to what time the crew will keep: I suspect that they'll be in whatever time zone is most convenient for the key mission events.
www.asi.org /adb/04/05/lunar-time-zone.html   (318 words)

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