digplanet beta 1: Athena
Share digplanet:


Applied sciences






















Geocentric Coordinate Time (TCG - Temps-coordonnée géocentrique) is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to precession, nutation, the Moon, and artificial satellites of the Earth. It is equivalent to the proper time experienced by a clock at rest in a coordinate frame co-moving with the center of the Earth: that is, a clock that performs exactly the same movements as the Earth but is outside the Earth's gravity well. It is therefore not influenced by the gravitational time dilation caused by the Earth.

TCG was defined in 1991 by the International Astronomical Union, in Recommendation III of the XXIst General Assembly. It was intended as one of the replacements for the ill-defined Barycentric Dynamical Time (TDB). Unlike former astronomical time scales, TCG is defined in the context of the general theory of relativity. The relationships between TCG and other relativistic time scales are defined with fully general relativistic metrics.

Because the reference frame for TCG is not rotating with the surface of the Earth and not in the gravitational potential of the Earth, TCG ticks faster than clocks on the surface of the Earth by about 7.0 × 10−10 (about 22 milliseconds per year). Consequently, the values of physical constants to be used with calculations using TCG differ from the traditional values of physical constants. (The traditional values were in a sense wrong, incorporating corrections for the difference in time scales.) Adapting the large body of existing software to change from TDB to TCG is a formidable task, and as of 2002 many calculations continue to use TDB in some form.

Time coordinates on the TCG scale are conventionally specified using traditional means of specifying days, carried over from non-uniform time standards based on the rotation of the Earth. Specifically, both Julian Dates and the Gregorian calendar are used. For continuity with its predecessor Ephemeris Time, TCG was set to match ET at around Julian Date 2443144.5 (1977-01-01T00Z). More precisely, it was defined that TCG instant 1977-01-01T00:00:32.184 exactly corresponds to TAI instant 1977-01-01T00:00:00.000 exactly. This is also the instant at which TAI introduced corrections for gravitational time dilation.

TCG is a Platonic time scale: a theoretical ideal, not dependent on a particular realisation. For practical purposes, TCG must be realised by actual clocks in the Earth system. Because of the linear relationship between Terrestrial Time (TT) and TCG, the same clocks that realise TT also serve for TCG. See the article on TT for details of the relationship and how TT is realised.

Barycentric Coordinate Time (TCB) is the equivalent of TCG for calculations relating to the solar system beyond Earth orbit. TCG is defined by a different reference frame from TCB, such that they are not linearly related. Over the long term, TCG ticks more slowly than TCB by about 1.6 × 10−8. In addition there are periodic variations, as Earth moves within the Solar system. When the Earth is at perihelion in January, TCG ticks even more slowly than it does on average, due to gravitational time dilation from being deeper in the Sun's gravity well and also velocity time dilation from moving faster relative to the Sun. At aphelion in July the opposite holds, with TCG ticking faster than it does on average.

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Geocentric_Coordinate_Time — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
115 videos foundNext > 

Line 22 7b97z57h Conversions Geocentric Geographic UFO Mapping 5g WOW SETI

http://alienspacesciencenews.wordpress.com/ 7b97z57h 100 videos there are more videos after this one i'll post all then update the #. Math Equation Wow Seti ...

The implications of geocentrism

Before you act out like an emotional retarded zombie chimp.. check these links out... https://www.youtube.com/watch?v=p8cBvMCucTg now look! keep in mind thes...

The total lunar eclipse of 28 September 2015

The total lunar eclipse of 28 September 2015 in equatorial coordinates for a geocentric observer. The time is in UTC. Note that a faint star is occulted by d...

The total lunar eclipse of 14/15 April 2014

The total lunar eclipse of 14/15 April 2014 in equatorial coordinates for a geocentric observer. The time is in UTC. Source: http://hemel.waarnemen.com/maan/...

iTraject - Orbital Mechanics App

iTraject, is a trajectory simulation in Earth Moon System which makes space flight easy for everyone. This powerful educational application, thanks to its nu...

Projected Coordinate Systems

Description of UTM and SPCS.

Geocentric Movement of the Solar System and the Hindu Lunar Calendar

This animation illustrates the Hindu lunar months (Masa) using the year 2013 as an example. The animation starts with Apr 14th 2013 which is the solar New Ye...

Astronomy with MicroStation Local Coordinate Frame

Created with MicroStation http://www.Bentley.com , this clip explains the derivation of local or Altazimuthal coordinate frame used in observational astronom...

Celestial coordinates of fixed stars

One can think of the celestial sphere of fixed stars as immobile. In this case, it is the Earth which rotates around its own axis.

Triton Ocean SDK 2014 Demo

The Triton Ocean SDK from Sundog Software brings fast, realistic 3D ocean and water effects to OpenGL and DirectX developers. Triton is capable of simulating...

115 videos foundNext > 

We're sorry, but there's no news about "Geocentric Coordinate Time" right now.


Oops, we seem to be having trouble contacting Twitter

Talk About Geocentric Coordinate Time

You can talk about Geocentric Coordinate Time with people all over the world in our discussions.

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!