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15.5.148 dtdb

dtdb(jdtt, ut, elong, u, v)

[SOFA] Returns an approximation of TDB-TT in seconds, the difference between barycentric dynamical time and terrestrial time, for an observer on the Earth. jdtt is the Julian Date in TDB or TT, ut is the Universal Time measured in fractions of a day, elong is the east longitude in radians, u is the distance in km from the Earth spin axis, and v is the distance in km north of the equatorial plane. jdtt and ut should have the same dimensions. The remaining parameters must be scalars or arrays with exactly one element.

This function is merely a model; numerical integration of solar-system ephemeris is the definitive method for predicting the relationship between tcg and tcb, and hence between TT and TDB. The absolute accuracy of the sofa routine underlying the present LUX function is better than 3 ns during the interval 1950-2050.

See also: Astronomical Coordinate Calculations