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Barycentric Coordinate Time (TCB, from the French Temps-coordonnée barycentrique) is a coordinate time standard intended to be used as the independent variable of time for all calculations pertaining to orbits of planets, asteroids, comets, and interplanetary spacecraft in the Solar system. It is equivalent to the proper time experienced by a clock at rest in a coordinate frame co-moving with the barycenter of the Solar system: that is, a clock that performs exactly the same movements as the Solar system but is outside the system's gravity well. It is therefore not influenced by the gravitational time dilation caused by the Sun and the rest of the system.

TCB was defined in 1991 by the International Astronomical Union, in Recommendation III of the XXIst General Assembly.[1] It was intended as one of the replacements for the ill-defined Barycentric Dynamical Time (TDB). Unlike former astronomical time scales, TCB is defined in the context of the general theory of relativity. The relationships between TCB and other relativistic time scales are defined with fully general relativistic metrics.

Because the reference frame for TCB is not influenced by the gravitational potential caused by the Solar system, TCB ticks faster than clocks on the surface of the Earth by 1.550505 × 10−8 (about 490 milliseconds per year). Consequently, the values of physical constants to be used with calculations using TCB 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 TCB is a formidable task, and as of 2002 many calculations continue to use TDB in some form.

Time coordinates on the TCB 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, TCB was set to match ET at around Julian Date 2443144.5 (1977-01-01T00Z). More precisely, it was defined that TCB instant 1977-01-01T00:00:32.184 exactly corresponds to the TAI instant 1977-01-01T00:00:00.000 exactly, at the geocenter. This is also the instant at which TAI introduced corrections for gravitational time dilation.

## References

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Barycentric_Coordinate_Time — Please support Wikipedia.
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 WT65: Barycentric coordinates and the 6-7-8 triangleHere we present another solution to the 6-7-8 triangle problem, this time using barycentric coorindates. This gives us a chance to apply the idea of assignin... Complex Barycentric Coordinates with Applications to Planar Shape DeformationBarycentric coordinates are heavily used in computer graphics applications to generalize a set of given data values. Traditionally, the coordinates are requi... Phys App - Barycentric Coordinates.avi OpenGL RaytracerThis OpenGL program is a classic backwards raytracer that supports full phong illumination as well as sphere and triangle intersection. It uses barycentric c... The Sun's Motion Around the Solar System BarycenterSome time ago an online user tried to claim that the sun sits at the center of the solar system, and that the solar system's center of gravity stays inside t... Orkid Software Renderer (A-Buffered)Disabled the Z-buffer. Enabled the A-Buffer(Fragment Compositor and Hider). Colored by Barycentric coordinates. 3D Software Renderer3D Software Based Renderer Language: C++ API: GDI Features: Import multiple OBJ models Wireframe rendering Render using one constant color Idle rotation Back... The Solar System's BarycenterThe Sun and solar system orbit a barycenter (center of mass) that occasionally will go slightly above the sun's surface. This is due to the pull of the plane... Comet ISON with picturesComet ISON or C/2012 S1 will come to perihelion (closest approach to the Sun) on 28 November 2013 at a distance of 0.0124 AU (1860000 km; 1150000 mi) fro... How to Pronounce BarycentricLearn how to say Barycentric correctly with EmmaSaying's "how do you pronounce" free tutorials. Definition of barycentric (oxford dictionary): adjective rela...
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