gst00b¶
- erfa.gst00b(uta, utb)[source]¶
Greenwich apparent sidereal time (consistent with IAU 2000 resolutions but using the truncated nutation model IAU 2000B).
- Parameters:
- utadouble array
- utbdouble array
- Returns:
- c_retvaldouble array
Notes
Wraps ERFA function
eraGst00b
. The ERFA documentation is:- - - - - - - - - - e r a G s t 0 0 b - - - - - - - - - - Greenwich apparent sidereal time (consistent with IAU 2000 resolutions but using the truncated nutation model IAU 2000B). Given: uta,utb double UT1 as a 2-part Julian Date (Notes 1,2) Returned (function value): double Greenwich apparent sidereal time (radians) Notes: 1) The UT1 date uta+utb is a Julian Date, apportioned in any convenient way between the argument pair. For example, JD(UT1)=2450123.7 could be expressed in any of these ways, among others: uta utb 2450123.7 0.0 (JD method) 2451545.0 -1421.3 (J2000 method) 2400000.5 50123.2 (MJD method) 2450123.5 0.2 (date & time method) The JD method is the most natural and convenient to use in cases where the loss of several decimal digits of resolution is acceptable. The J2000 and MJD methods are good compromises between resolution and convenience. For UT, the date & time method is best matched to the algorithm that is used by the Earth Rotation Angle function, called internally: maximum precision is delivered when the uta argument is for 0hrs UT1 on the day in question and the utb argument lies in the range 0 to 1, or vice versa. 2) The result is compatible with the IAU 2000 resolutions, except that accuracy has been compromised for the sake of speed and convenience in two respects: . UT is used instead of TDB (or TT) to compute the precession component of GMST and the equation of the equinoxes. This results in errors of order 0.1 mas at present. . The IAU 2000B abridged nutation model (McCarthy & Luzum, 2003) is used, introducing errors of up to 1 mas. 3) This GAST is compatible with the IAU 2000 resolutions and must be used only in conjunction with other IAU 2000 compatible components such as precession-nutation. 4) The result is returned in the range 0 to 2pi. 5) The algorithm is from Capitaine et al. (2003) and IERS Conventions 2003. Called: eraGmst00 Greenwich mean sidereal time, IAU 2000 eraEe00b equation of the equinoxes, IAU 2000B eraAnp normalize angle into range 0 to 2pi References: Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to implement the IAU 2000 definition of UT1", Astronomy & Astrophysics, 406, 1135-1149 (2003) McCarthy, D.D. & Luzum, B.J., "An abridged model of the precession-nutation of the celestial pole", Celestial Mechanics & Dynamical Astronomy, 85, 37-49 (2003) McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), IERS Technical Note No. 32, BKG (2004) This revision: 2021 May 11 Copyright (C) 2013-2023, NumFOCUS Foundation. Derived, with permission, from the SOFA library. See notes at end of file.