USNO Circular 179 - U.S. Naval Observatory

Recommendations

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68 IAU RESOLUTIONS 1997 reference frames, to maintain the ICRF and its ties to the reference frames at other wavelengths. Note 1: IERS 1995 Report, Observatoire de Paris, p. II-19 (1996). Note 2: “The extragalactic reference system of the International Earth Rotation Service (ICRS)”, Arias, E.F. et al. A & A 303, 604 (1995). Resolution B4 On Non-Rigid Earth Nutation Theory The XXIIIrd International Astronomical Union General Assembly Recognizing that the International Astronomical Union and the International Union of Geodesy and Geophysics Working Group (IAU-IUGG WG) on Non-rigid Earth Nutation Theory has met its goal by identifying the remaining geophysical and astronomical phenomena that must be modeled before an accurate theory of nutation for a non-rigid Earth can be adopted, and that, as instructed by IAU Recommendation C1 in 1994, the International Earth Rotation Service (IERS) has published in the IERS Conventions (1996) an interim precession-nutation model that matches the observations with an uncertainty of ± 1 milliarcsecond (mas), endorses the conclusions of the IAU-IUGG WG on Non-rigid Earth Nutation Theory given in the appendix, requests the IAU-IUGG WG on Non-rigid Earth Nutation Theory to present a detailed report to the next IUGG General Assembly (August 1999), at which time the WG will be discontinued, and urges the scientific community to address the following questions in the future: - completion of a new rigid Earth nutation series with the additional terms necessary for the theory to be complete to within ± 5 microarcseconds, and - completion of a new non-rigid Earth transfer function for an Earth initially in non-hydrostatic equilibrium, incorporating mantle inelasticity and a Free Core Nutation period in agreement with the observations, and taking into account better modeling of the fluid parts of the planet, including dissipation. APPENDIX The WG on Non-rigid Earth Nutation Theory has quantified the problems in the nutation series adopted by the IAU in 1980 by noting: (1) that there is a difference in the precession rate of about −3.0 milliarcseconds per year (mas/year) between the value observed by Very Long Baseline Interferometry (VLBI) and Lunar Laser Ranging (LLR) and the adopted value,
IAU RESOLUTIONS 1997 69 (2) that the obliquity has been observed (by VLBI and LLR) to change at a rate of about −0.24 mas/year, although there is no such change implied by the 1980 precession-nutation theory, (3) that, in addition to these trends, there are observable peak-to-peak differences of up to 20 milliarcseconds (mas) between the nutation observed by VLBI and LLR and the nutation adopted by the IAU in 1980, (4) that these differences correspond to spectral amplitudes of up to several mas, and (5) that the differences between observation and theory are well beyond the present observational accuracy. The WG has recognized the improvements made in the modeling of these quantities, and recommends, in order to derive a more precise nutation model, at the mas level in spectral amplitudes and at a few mas level in the peak to peak analysis, the use of models: (1) based on a new non-rigid Earth transfer function for an Earth initially in non-hydrostatic equilibrium, incorporating mantle inelasticity, a core-mantle-boundary flattening giving a Free Core Nutation (FCN) period in agreement with the observed value, and a global Earth dynamical flattening in agreement with the observed precession, and (2) based on a new rigid Earth nutation series which takes into account the following perturbing effects: 1. in lunisolar ephemerides: indirect planetary effects, lunar inequality, J2-tilt, planetarytilt, secular variations of the amplitudes, effects of precession and nutation, 2. in the perturbing bodies to be considered: in addition to the Moon and the Sun, the direct planetary effects of Venus, Jupiter, Mars, and Saturn, should be included, 3. in the order of the external potential to be considered: J3 and J4 effects for the Moon, and 4. in the theory itself: effects of the tri-axiality of the Earth, relativistic effects and second order effects. The WG recognizes that this new generation of models still has some imperfections, the principal one being poor modeling of the dissipation in the core and of certain effects of the ocean and the atmosphere, and urges the scientific community to address these questions in the future. The WG recognizes that, due to the remaining imperfections of the present theoretical nutation models, the nutation series published in the IERS Conventions (1996), following 1994 IAU recommendation C1, still provides the users with the best nutation series. This IERS model being based on observations of the celestial pole offset, the WG supports the recommendation that the scientific community continue VLBI and LLR observations to provide accurate estimations of nutation, precession and rate of change in obliquity.
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UNITED STATES NAVAL OBSERVATORY CIR
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ii 3.4.4 Relationship to Other Syst
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iv INTRODUCTION recommendations. Ma
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vi INTRODUCTION that are available
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A Few Words about Constants This ci
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Abbreviations and Symbols Frequentl
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xii ABBREVIATIONS & SYMBOLS s CIO l
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2 RELATIVITY In 1991, the IAU made
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4 RELATIVITY Geocentric Celestial R
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6 RELATIVITY 1.4 Concluding Remarks
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8 TIME SCALES star across a certain
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10 TIME SCALES were computed in a b
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12 TIME SCALES Clearly UT1-UTC and
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14 TIME SCALES From the perspective
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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 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 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
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USNO Circular 179 - U.S. Naval Observatory

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