Nicole Capitaine
Observatoire de Paris, SYRTE, Emeritus
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This paper investigates the practical use of the nonrotating origin (NRO) (Guinot 1979) for estimating the Earth Rotation Parameters from VLBI data, which is based on the rotational transformation between the geocentric celestial and... more
This paper investigates the practical use of the nonrotating origin (NRO) (Guinot 1979) for estimating the Earth Rotation Parameters from VLBI data, which is based on the rotational transformation between the geocentric celestial and terrestrial frames as previously derived by Capitaine (1990). Numerical checks of consistency show that the transformation referred to the NRO is equivalent to the classical one referred to the equinox and considering the complete “equation of the equinoxes” (Aoki & Kinoshita 1983). The paper contains the expressions for the partial derivatives of the VLBI geometric delay to be used for the adjustment of the pole coordinates, UT1 and deficiencies in the two celestial coordinates of the Celestial Ephemeris Pole (CEP) in the multiparameters fits to VLBI data. The use of the NRO is shown to simplify the estimates of these parameters and to free the estimated UT1 parameter from the model for precession and nutation.
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ABSTRACT The Journees 2011, with the sub-title "Earth rotation, reference systems and celestial mechanics: Synergies of geodesy and astronomy", were organized at Bundesamt fur Eich- und Vermessungswesen (BEV), Vienna,... more
ABSTRACT The Journees 2011, with the sub-title "Earth rotation, reference systems and celestial mechanics: Synergies of geodesy and astronomy", were organized at Bundesamt fur Eich- und Vermessungswesen (BEV), Vienna, from 19 to 21 September 2011. They were the 21st meeting in the Journees conference series, which provide an international forum for advanced discussion in the fields of space and time reference systems, Earth rotation, dynamics of the solar system, astrometry and time. The Journees 2011 were focused on issues related to recent developments in fundamental astronomy, time and relativity, plans for the next generation of space-time reference systems, astronomical space and time reference systems, Earth rotation and global geodynamics, celestial mechanics of solar system bodies, space observations and dedicated missions for geodesy and astronomy. There were presentations and discussions related to the Division 1 IAU Working Groups and Division 1 commissions.
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Report of the IAU WGAS (Working Group on Astronomical Standards) sub - working group on relativity in celestial mechanics and astrometry (RCMA SWG).
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Analysis of Lunar Laser ranging observations allows to determine a number of parameters related to the dynamics of the Earth-Moon system. It also contributes to the determination of the Earth Orientation Parameters (EOP) such as... more
Analysis of Lunar Laser ranging observations allows to determine a number of parameters related to the dynamics of the Earth-Moon system. It also contributes to the determination of the Earth Orientation Parameters (EOP) such as precession-nutation, polar motion and UT1. Here, we focus on the determination of the precession-nutation corrections DX , DY to the conventional model for the coordinates of the CIP (Celestial Intermediate Pole) in the GCRS (Geocentric Celestial Reference System), which are used in this study, instead of the classical parameters determined in previous works.
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Research Interests: Humanities and Art
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We analyze the impact of the installation of a lunar laser ranging device on the NTT 3.6m ESO telescope. With such an instrument, the scientific communities of fundamental physics and solar system formation will highly benefit of the only... more
We analyze the impact of the installation of a lunar laser ranging device on the NTT 3.6m ESO telescope. With such an instrument, the scientific communities of fundamental physics and solar system formation will highly benefit of the only LLR station in the Southern Hemisphere. The quality of the NTT 3.6 meter telescope will also greatly complement the LLR 3.5 meter Apache Point telescope (3.5 m) instrument in the Northern Hemisphere (USA) which is the best instrument for tracking the Moon since 2006. Finally, we also consider the technical characteristics of such installation including the observational constraints.
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Research Interests: Astrobiology and EAA
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Fedorov's work has played an important role in the evolution of ideas and knowledge on Earth rotation, especially for the best choice of the axis of reference for nutation both in theory and observation and for the effects of the... more
Fedorov's work has played an important role in the evolution of ideas and knowledge on Earth rotation, especially for the best choice of the axis of reference for nutation both in theory and observation and for the effects of the non-rigidity of the Earth. These two problems are still under discussion in the astronomical community after the adoption of the International Reference System, ICRS, within two IAU Working Groups, one on the "Non-rigid Earth nutation theory" and the second considering the possible extension of the definition of the "Celestial Ephemeris Pole". Fedorov's memorial conference is an opportunity to replace Fedorov's work in the present discussion.
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The IAU Working Group (WG) on Numerical Standards for Fundamental Astronomy has been tasked with updating the IAU Current Best Estimates (CBEs). In addition to the need to update the CBEs because of improved estimates, there have also... more
The IAU Working Group (WG) on Numerical Standards for Fundamental Astronomy has been tasked with updating the IAU Current Best Estimates (CBEs). In addition to the need to update the CBEs because of improved estimates, there have also been significant changes that ...
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Earth rotation based on the celestial coordinates of the celestial intermediate pole I. The dynamical equations
It has been demonstrated that the analysis of Lunar Laser Ranging (LLR) observations could bring scientific results in various domains including astronomy, gedoynamics and gravitational physics. Here, we focus on the contribution of the... more
It has been demonstrated that the analysis of Lunar Laser Ranging (LLR) observations could bring scientific results in various domains including astronomy, gedoynamics and gravitational physics. Here, we focus on the contribution of the LLR in determining the Earth Orientation Parameters (EOP), especially, the direction towards the Celestial Intermediate Pole (CIP) in the Geocentric Celestial reference System. The strategy we have followed, consists in : first, calculating the LLR residuals over a period of more than 37 years, using the IAU 2006-2000A model of precession-nutation (i.e MHB 2000 nutation of Mathews et al. 2002 and P03 precession of Capitaine et al. 2003) and the CIO based procedure. Second, determining the GCRS X and Y coordinates of the Celestial Intermediate Pole at regular interval (i.e in our case, every 70 days). Finally, comparing the results obtained with VLBI observations in order to evaluate the potential of LLR as compared to VLBI for estimating the X, Y qua...
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IAU Commission 19 began in 1919 with the birth of the IAU at the Brussels Conference, where Standing Committee 19 on Latitude Variations was established as one of 32 standing committees. At the first IAU General Assembly in 1922, Standing... more
IAU Commission 19 began in 1919 with the birth of the IAU at the Brussels Conference, where Standing Committee 19 on Latitude Variations was established as one of 32 standing committees. At the first IAU General Assembly in 1922, Standing Committee 19 became Commission 19 “Variation of Latitude”. In the beginning, the main topic of the Commission was the investigation of polar motion. Later, its activities included observations and theory of Earth rotation and connections between Earth orientation variations and geophysical phenomena. As a result, in 1964 at the XII IAU General Assembly, the Commission was renamed “Rotation of the Earth”. The investigation of Earth orientation variations is primarily based on observations of natural and artificial celestial objects. Therefore, maintenance of the international terrestrial and celestial reference frames, as well as the coordinate transformation between the frames and the improvement of the model of precession/nutation, have always bee...
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The IAU Division I Working Group on Nomenclature for Fundamental Astronomy (NFA) was established by the IAU XXV General Assembly with the task of providing proposals for new nomenclature associated with the implementation of the IAU XXIV... more
The IAU Division I Working Group on Nomenclature for Fundamental Astronomy (NFA) was established by the IAU XXV General Assembly with the task of providing proposals for new nomenclature associated with the implementation of the IAU XXIV GA resolutions (2000) and to make related educational efforts for bringing the issue to the notice of scientists in the community.
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We recall the concepts and nomenclature associated with the IAU 2000 definition of UT1 as function of the Earth rotation angle (ERA). We comment on the complications that arise when UT1 is regarded as both an angle and a time scale. We... more
We recall the concepts and nomenclature associated with the IAU 2000 definition of UT1 as function of the Earth rotation angle (ERA). We comment on the complications that arise when UT1 is regarded as both an angle and a time scale. We review the IAU 2006 expressions for the position of the celestial intermediate origin (CIO) and the equation of the origins, and the associated CIO and equinox based procedures for the celestial-to-terrestrial transformation.
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Division I provides a focus for astronomers studying a wide range of problems related to fundamental physical phenomena such as time, the inertial reference frame, positions and proper motions of celestial objects, and precise dynamical... more
Division I provides a focus for astronomers studying a wide range of problems related to fundamental physical phenomena such as time, the inertial reference frame, positions and proper motions of celestial objects, and precise dynamical computation of the motions of bodies in stellar or planetary systems in the Universe.
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The IAU Commission 52 “Relativity in Fundamental Astronomy” (RIFA) has been established during the 26th General Assembly of the IAU (Prague, 2006) to centralize the efforts in the field of Applied Relativity and to provide an official... more
The IAU Commission 52 “Relativity in Fundamental Astronomy” (RIFA) has been established during the 26th General Assembly of the IAU (Prague, 2006) to centralize the efforts in the field of Applied Relativity and to provide an official forum for corresponding discussions.
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Global determinations of polar, motion are now made by two kinds of methods: the astronomical method as used by the International Polar Motion Service (IPMS) (Yumi, 1973) or by the Bureau International de l’Heure (BIH) (Guinot, Feissel... more
Global determinations of polar, motion are now made by two kinds of methods: the astronomical method as used by the International Polar Motion Service (IPMS) (Yumi, 1973) or by the Bureau International de l’Heure (BIH) (Guinot, Feissel and Granveaud, 1971), and the method based on Doppler measurements on artificial satellites as used by the Dahlgren Polar Monitoring Service (DPMS) since 1967 (Anderle,1970). In addition, there are local methods used to compute the latitude variations of isolated stations from laser or Doppler measurements.
A new procedure has been devised for computing apparent places of stars in the intermediate frame (Capitaine 1990) linked to the nonrotating origin (Guinot 1979) for estimating the Earth rotation parameters (ERP) from astrometric... more
A new procedure has been devised for computing apparent places of stars in the intermediate frame (Capitaine 1990) linked to the nonrotating origin (Guinot 1979) for estimating the Earth rotation parameters (ERP) from astrometric observations. The latitude and time parameters as derived by this procedure have been compared to the parameters as derived from the classical procedure used for the reduction of Paris astrolabe observations (Chollet 1984). The consistency between the two procedures has been found to be of the order of a few 10−4ʺ, which is under the order of precision of the computations in the classical procedure. The new procedure, which is more directly related to the Earth rotation, is proposed to be used for the derivation of the ERP in the Hipparcos frame from existing astrometric observations, which is planned for the near future (IAU WG on “Earth Rotation in the Hipparcos Reference Frame”).
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The current IAU conventional models for precession and nutation are referred to the Celestial Ephemeris Pole (CEP). However, the concept corresponding to the CEP is not clear and cannot easily be extended to the most recent models and... more
The current IAU conventional models for precession and nutation are referred to the Celestial Ephemeris Pole (CEP). However, the concept corresponding to the CEP is not clear and cannot easily be extended to the most recent models and observations. Its realization is actually dependent both on the model used for precession, nutation and polar motion and on the observational procedure for estimating the Earth orientation parameters. A new definition of the CEP should therefore be given in order to be in agreement with modern models and observations at a microarsecond level. This paper reviews the various realizations of the pole according to the models and observations and discusses the proposals for a modern definition of the CEP that are under consideration within the work of the subgroup T5 entitled “Computational Consequences” of the “ICRS” IAU Working Group.
In order to give an exact and clear description of the angle of rotation of the Earth, we propose to use, as the reference point in space, a “non-rotating origin” (Guinot 1979) such that its hour angle, reckoned from the origin of the... more
In order to give an exact and clear description of the angle of rotation of the Earth, we propose to use, as the reference point in space, a “non-rotating origin” (Guinot 1979) such that its hour angle, reckoned from the origin of the longitudes (or “non-rotating origin” in the Earth), represents strictly the specific rotation of the Earth. The position of this origin on the instantaneous equator depends only on the trajectory of the pole of rotation. We show that the estimation of the deduced angle of rotation is not critically affected by the precision with which this trajectory is known. We give therefore the formulae to obtain the non-rotating origin, at any date t, from a chosen fixed reference, and we propose a definition of the Universal Time which will remain valid, even if the adopted model for the precession and the nutation is revised. We show that the use of the non-rotating origin also simplifies the transformation of coordinates between the terrestrial and celestial re...
The adoption of the International Celestial Reference System (ICRS) by the IAU in use since 1 January 1998, and the accuracy achieved by the most recent models and observations of Earth rotation call for a redefinition of the Earth... more
The adoption of the International Celestial Reference System (ICRS) by the IAU in use since 1 January 1998, and the accuracy achieved by the most recent models and observations of Earth rotation call for a redefinition of the Earth Orientation Parameters (EOP). First, the precession-nutation parameters and Greenwich sidereal time, which are currently defined in the FK5 System, have to be re-defined to be consistent with the ICRS. Second, the current definition of the Celestial Ephemeris Pole (CEP) has to be extended in order to be consistent with the most recent models for nutation and polar motion at a microarsecond accuracy including diurnal and sub-diurnal components, as well as with new strategies of observations. Such issues have been under consideration by the subgroup T5 named “Computational Consequences” of the IAU Working Group “ICRS”. This paper gives, as the basis for future recommendations, the preliminary proposals of the subgroup T5 for a modern definition of the CEP, ...
Research Interests: Observation, Kinematics, Motion, Accuracy, Ephemerides, and 5 morePrecession, Precision, Rotation, Parameters, and Euler angles
The IAU Commission 4 Working Group on Standardizing Access to Ephemerides recommends the use of the Spacecraft and Planet Kernel (SPK) format to provide a uniform format for the position ephemerides of planets and other natural solar... more
The IAU Commission 4 Working Group on Standardizing Access to Ephemerides recommends the use of the Spacecraft and Planet Kernel (SPK) format to provide a uniform format for the position ephemerides of planets and other natural solar system bodies, and the use of the Planetary Constants Kernel (PCK) for the orientation of these bodies. These formats are used by the SPICE system, developed by the Navigation and Ancillary Information Facility of NASA's Jet Propulsion Laboratory. The working group's final report is currently undergoing final preparations for publication. A long version of this report will be available at the IAU Commission 4: Ephemerides (or its successor) web site. This long version will contain a full description of that portion of the SPK and PCK formats required to duplicate these file types for this application.
Two Resolutions have been submitted to the 24thGeneral Assembly of the IAU concerning the definition and use of the celestial pole of reference and the celestial origin. The aim of both resolutions is to provide new parameters for Earth... more
Two Resolutions have been submitted to the 24thGeneral Assembly of the IAU concerning the definition and use of the celestial pole of reference and the celestial origin. The aim of both resolutions is to provide new parameters for Earth rotation which are consistent with the properties of the International Celestial Reference System (ICRS), adopted from 1 January 1998 as the IAU celestial reference system. The definition of the parameters have also to be consistent with the precision and the temporal resolution of the current Earth rotation measurements as well as with the theory for nutation and polar motion at the microarcsecond level. This paper explains the basis of the resolutions as well as their practical application. One of the resolutions defines the “Celestial Intermediate Pole” (CIP) in order to replace the “Celestial Ephemeris Pole” (CEP) for the new IAU precession-nutation model; its specifies the way for taking into account the constant offset from the ICRS and the hig...