PDF《SOFA software support for IAU 2000》

2004 Denver,

2004 May

31 The quantity s The quantity s -0.1 -0.08 -0.06 -0.04 -0.02

0 0.02 0.04 0.06 0.08 0.1

1900 1950

2000 2050

2100 Julian epoch s / arcsecond AAS

2004 Denver,

2004 May

31 SOFA provision for IAU

2000 ? SOFA supports both the new (CEO-based) and the classical (equinox-based) procedures. ? The CEO-based algorithms are definitive, but the classical equivalents deliver equal accuracy for practical purposes. ? Both IAU 2000A and IAU 2000B are supported. ? The IAU 2000B nutation series is almost as accurate (1 mas) as the full IAU 2000A series, despite being shorter than the IAU

1976 series. ? All these choices mean that IAU

2000 support accounts for nearly a third of the

121 SOFA routines. ? The routines range from building blocks (e.g. compute nutation ?ψ,?ε) to high-level ensembles (e.g. compute celestial-to-terrestrial matrix), enabling different simplicity/efficiency trade-offs. AAS

2004 Denver,

2004 May

31 Using the SOFA software ? The improved classical procedures are, as far as possible, "plug-compatible" with existing ones. ? However, frame bias is new, and GST requires both UT and TT, so applications will need to be changed accordingly. ? You don't have to understand the new CEO-based methods in order to benefit from the improved accuracy. ? But for newcomers the CEO/ERA method is simpler. ? SOFA is Fortran-only at present. ? Programmers in C++, Java etc. can use the SOFA routines as blueprints and benchmarks. AAS

2004 Denver,

2004 May

31 Other software supporting IAU

2000 ? IAU2000A: MHB_2000 nutation ? IAU2000B: abbreviated nutation ? XYS2000A: X, Y and s ? GMST2000: GMST ? GST2000: GST ? EE2000: equation of the equinoxes ? EECT2000: complementary terms In preparation: ? ERA2000: Earth Rotation Angle ? SP2000: s' ? T2C2000: TRS-to-CRS matrix ? POM2000: polar motion matrix ? CBPN2000: classical bpn matrix ? BPN2000: new N?P?B matrix ? NU2000A: nutation, IAU 2000A ? NU2000B: nutation, IAU 2000B IERS routines: http://maia.usno.navy.mil/ch5subs.html ? NOVAS ? SLALIB AAS

2004 Denver,

2004 May

31 Greenwich Hour Angles, old and new: methods space motion parallax light deflection aberration ICRS α,δ etc. precession nutation Greenwich Mean Sidereal Time equation of the equinoxes frame bias GCRS → CIP,CEO Earth Rotation Angle h,δ polar motion AAS

2004 Denver,

2004 May

31 Greenwich hour angles, old and new: example

2004 May 31, 22h UTC λ = ?104.9950, φ = +39.7427 Fictitious star Old-style prediction using Sidereal Time ICRS

23 32 55.171 +52

16 38.29 Apparent RA,Dec

23 33 06.176 +52

17 43.50 Local HA,Dec +

8 05 50.276 +52

17 43.66 New-style prediction using Earth Rotation Angle ICRS

23 32 55.171 +52

16 38.29 Intermediate RA,Dec

23 32 53.329 +52

17 43.50 Local HA,Dec +

8 05 50.276 +52

17 43.66