USNO Circular 179 - U.S. Naval Observatory

Recommendations

Info

xii ABBREVIATIONS & SYMBOLS s CIO locator: the difference between two arcs on the celestial sphere, providing the direction toward the CIO 6.5.1.3 SI Système International d’Unités (International System of Units) SOFA Standards of Fundamental Astronomy (software) T unless otherwise specified, time in Julian centuries (36525 days of 86400 seconds) from JD 2451545.0 (2000 Jan 1.5) (The time scale used should be specified, otherwise TT is understood.) Teph time argument of JPL planetary and lunar ephemerides 2.2, 4.2 TAI International Atomic Time 2.2 TCB Barycentric 1 Coordinate Time 1.2, 2.2 TCG Geocentric Coordinate Time 1.2, 2.2 TDB Barycentric 1 Dynamical Time 2.2 TIO Terrestrial Intermediate Origin 2 6.2, 6.5.2 TIRS (See Eϖ) TT Terrestrial Time 2.2 UCAC USNO CCD Astrographic Catalog 3.4.5 USNO U.S. Naval Observatory UT1 Universal Time (affected by variations in length of day) 2.3, 2.6.2 UTC Coordinated Universal Time (an atomic time scale) 2.4 VLBI very long baseline [radio] interferometry W “wobble” (polar motion) matrix (for transformation from ITRS to Eϖ) 6.5.2 WGS⎫ 84 X ⎪⎬ World Geodetic System 1984 6.4 Y Z ⎪⎭ components of nGCRS , unit vector toward the CIP with respect to the GCRS 5.4, 6.5.1 xp yp standard polar motion parameters, defining location of the CIP in the ITRS 1 “Barycentric” always refers to the solar system barycenter, the center of mass of all bodies in the solar system. 2 The fundamental reference points referred to here as the Celestial Intermediate Origin (CIO) and the Terrestrial Intermediate Origin (TIO) were called, respectively, the Celestial Ephemeris Origin (CEO) and the Terrestrial Ephemeris Origin (TEO) in the IAU resolutions of 2000. The IAU Working Group on Nomenclature for Fundamental Astronomy (URL 6) has recommended the change of nomenclature with no change in the definitions. The new terminology is already in use in The Astronomical Almanac and in IERS documents, and will undoubtedly be adopted by the IAU General Assembly in 2006. It is used throughout this circular, except in the verbatim text of the IAU resolutions. 3 The abbreviation CIO was used throughout much of the 20th century to designate the Conventional International Origin, the reference point for the measurement of polar motion. 6.5.2
Chapter 1 Relativity Relevant IAU resolutions: A4.I, A4.II, A4.III, A4.IV of 1991; B1.3, B1.4, B1.5 of 2000 Summary In 2000, the IAU defined a system of space-time coordinates for (1) the solar system, and (2) the Earth, within the framework of General Relativity, by specifying the form of the metric tensors for each and the 4-dimensional space-time transformation between them. The former is called the Barycentric Celestial Reference System (BCRS) and the latter is called the Geocentric Celestial Reference System (GCRS). The BCRS is the system appropriate for the basic ephemerides of solar system objects and astrometric reference data on galactic and extragalactic objects. The GCRS is the system appropriate for describing the rotation of the Earth, the orbits of Earth satellites, and geodetic quantities such as instrument locations and baselines. The analysis of precise observations inevitably involves quantities expressed in both systems and the transformations between them. 1.1 Background Although the theory of relativity has been with us for a century (Einstein’s first papers on special relativity were published in 1905), it has only been within the last few decades that it has become a routine consideration in positional astronomy. The reason is simply that the observational effects of both special and general relativity are small. In the solar system, deviations from Newtonian physics did not need to be taken into account — except for the advance of the perihelion of Mercury — until the advent of highly precise “space techniques” in the 1960s and 1970s: radar ranging, spacecraft ranging, very long baseline interferometry (VLBI), pulsar timing, and lunar laser ranging (LLR). More recently, even optical astrometry has joined the list, with wide-angle satellite measurements (Hipparcos) at the milliarcsecond level. Currently, the effects of relativity are often treated as small corrections added to basically Newtonian developments. But it has become evident that the next generation of instrumentation and theory will require a more comprehensive approach, one that encompasses definitions of such basic concepts as coordinate systems, time scales, and units of measurement in a relativistically consistent way. It may remain the case that, for many applications, relativistic effects can either be ignored or handled as second-order corrections to Newtonian formulas. However, even in such simple cases, the establishment of a self-consistent relativistic framework has benefits — it at least allows the physical assumptions and the errors involved to be more clearly understood. 1
Page 1: UNITED STATES NAVAL OBSERVATORY CIR
Page 4 and 5: ii 3.4.4 Relationship to Other Syst
Page 6 and 7: iv INTRODUCTION recommendations. Ma
Page 8 and 9: vi INTRODUCTION that are available
Page 10 and 11: A Few Words about Constants This ci
Page 12 and 13: Abbreviations and Symbols Frequentl
Page 16 and 17: 2 RELATIVITY In 1991, the IAU made
Page 18 and 19: 4 RELATIVITY Geocentric Celestial R
Page 20 and 21: 6 RELATIVITY 1.4 Concluding Remarks
Page 22 and 23: 8 TIME SCALES star across a certain
Page 24 and 25: 10 TIME SCALES were computed in a b
Page 26 and 27: 12 TIME SCALES Clearly UT1-UTC and
Page 28 and 29: 14 TIME SCALES From the perspective
Page 30 and 31: 16 TIME SCALES method and the time
Page 32 and 33: 18 TIME SCALES through the local ge
Page 34 and 35: 20 CELESTIAL REFERENCE SYSTEM 3.1 T
Page 36 and 37: 22 CELESTIAL REFERENCE SYSTEM the i
Page 38 and 39: 24 CELESTIAL REFERENCE SYSTEM 3.4 I
Page 40 and 41: 26 CELESTIAL REFERENCE SYSTEM withi
Page 42 and 43: 28 CELESTIAL REFERENCE SYSTEM the p
Page 44 and 45: 30 EPHEMERIDES DE200 nor DE405 have
Page 46 and 47: 32 EPHEMERIDES scaling. LB = 1.550
Page 48 and 49: 34 PRECESSION & NUTATION 5.1 Aspect
Page 50 and 51: 36 PRECESSION & NUTATION 5.2 Which
Page 52 and 53: 38 PRECESSION & NUTATION Figure 5.2
Page 54 and 55: 40 PRECESSION & NUTATION the pole o
Page 56 and 57: 42 PRECESSION & NUTATION and the re
Page 58 and 59: 44 PRECESSION & NUTATION 2. A rotat
Page 60 and 61: 46 PRECESSION & NUTATION ∆ɛ = N
Page 62 and 63: 48 PRECESSION & NUTATION S1 = sin (
Page 64 and 65:
Chapter 6 Modeling the Earth’s Ro
Page 66 and 67:
52 MODELING THE EARTH’S ROTATION
Page 68 and 69:
Page 70 and 71:
Page 72 and 73:
Page 74 and 75:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
68 IAU RESOLUTIONS 1997 reference f
Page 84 and 85:
Text of IAU Resolutions of 2000 Ado
Page 86 and 87:
72 IAU RESOLUTIONS 2000 Resolution
Page 88 and 89:
74 IAU RESOLUTIONS 2000 integrals t
Page 90 and 91:
76 IAU RESOLUTIONS 2000 g0i = − 4
Page 92 and 93:
78 IAU RESOLUTIONS 2000 3. that sem
Page 94 and 95:
80 IAU RESOLUTIONS 2000 Recommends
Page 96 and 97:
References Journal abbreviations: A
Page 98 and 99:
84 REFERENCES Høg, E., Fabricius,
Page 100 and 101:
86 REFERENCES Nelson, R. A., McCart
Page 102 and 103:
IAU 2000A Nutation Series The nutat
Page 104 and 105:
90 NUTATION SERIES Term i j= 1 Fund
Page 106 and 107:
Page 108 and 109:
Page 110 and 111:
Page 112 and 113:
Page 114 and 115:
100 NUTATION SERIES Term i j= 1 Fun
Page 116 and 117:
102 NUTATION SERIES Term i j= 1 Fun
Page 118:
Errata & Updates Errata in this cir
show all

USNO Circular 179 - U.S. Naval Observatory

Create successful ePaper yourself

Delete template?

Save as template?