scholarly journals Definition and realization of the celestial intermediate reference system

2007 ◽  
Vol 3 (S248) ◽  
pp. 367-373 ◽  
Author(s):  
N. Capitaine
Keyword(s):  
Reference System ◽  
Reference Systems ◽  
The Earth ◽  
Fundamental Astronomy ◽  
International Terrestrial Reference System ◽  
Terrestrial Reference System ◽  
Rotation Of The Earth ◽  
Definition Of ◽  
Sidereal Rotation ◽  
Celestial Reference System

AbstractThe transformation between the International Terrestrial Reference System (ITRS) and the Geocentric Celestial Reference system (GCRS) is an essential part of the models to be used when dealing with Earth's rotation or when computing directions of celestial objects in various systems. The 2000 and 2006 IAU resolutions on reference systems have modified the way the Earth orientation is expressed and adopted high accuracy models for expressing the relevant quantities for the transformation from terrestrial to celestial systems. First, the IAU 2000 Resolutions have refined the definition of the astronomical reference systems and transformations between them and adopted the IAU 2000 precession-nutation. Then, the IAU 2006 Resolutions have adopted a new precession model that is consistent with dynamical theories and have addressed definition, terminology or orientation issues relative to reference systems and time scales that needed to be specified after the adoption of the IAU 2000 resolutions. These in particular provide a refined definition of the pole (the Celestial intermediate pole, CIP) and the origin (the Celestial intermediate origin, CIO) on the CIP equator as well as a rigorous definition of sidereal rotation of the Earth. These also allow an accurate realization of the celestial intermediate system linked to the CIP and the CIO that replaces the classical celestial system based on the true equator and equinox of date. This talk explains the changes resulting from the joint IAU 2000/2006 resolutions and reviews the consequences on the concepts, nomenclature, models and conventions in fundamental astronomy that are suitable for modern and future realizations of reference systems. Realization of the celestial intermediate reference system ensuring a micro-arc-second accuracy is detailed.

scholarly journals A non-rotating origin on the instantaneous equator

1988 ◽  
Vol 128 ◽  
pp. 33-38 ◽  
Author(s):  
N. Capitaine ◽  
B. Guinot
Keyword(s):  
Specific Rotation ◽  
Universal Time ◽  
Reference Systems ◽  
The Earth ◽  
Adopted Model ◽  
Fixed Reference ◽  
Rotation Of The Earth ◽  
Definition Of ◽  
Clear Description ◽  
Angle Of Rotation

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 reference systems.

scholarly journals A Terrestrial Reference System Consistent with WGRS

1991 ◽  
Vol 127 ◽  
pp. 211-214 ◽  
Author(s):  
C. Boucher ◽  
Z. Altamimi
Keyword(s):  
Reference System ◽  
Terrestrial Reference Frame ◽  
Reference Systems ◽  
International Earth Rotation Service ◽  
Earth Orientation Parameters ◽  
Terrestrial Reference System ◽  
Definition Of ◽  
Orientation Parameters ◽  
Evolution With Time

AbstractThe IAU and IUGG has jointly established in 1988 an International Earth Rotation Service (IERS) which is in charge of the realization of conventional celestial and terrestrial reference systems, together with the determination of earth orientation parameters which connect them.The theoretical definition of the terrestrial reference system which is realized by IERS through a conventional terrestrial reference frame formed by SLR, LLR, VLBI and GPS stations is presented. In particular its origin, scale, orientation and evolution with time are reviewed, taking into account relativistic and deformation effects.

A re-interpretation of the definition of UT1

1988 ◽  
Vol 128 ◽  
pp. 39-40
Author(s):  
A. T. Sinclair
Keyword(s):  
Time Scale ◽  
Universal Time ◽  
Sidereal Time ◽  
Broad Definition ◽  
The Earth ◽  
Average Person ◽  
Rotation Of The Earth ◽  
Definition Of ◽  
Sidereal Rotation

SummaryUniversal time is a commonplace quantity, and yet it has no generally accepted definition. The expression for sidereal time is often quoted as a definition, but this does not convey much meaning to the average person. Also sidereal time is measured from the equinox of date, and so involves the precession formulae of the stellar reference frame, and hence may not be ideal for other modern techniques of observation. Guinot (1979) has proposed a broad definition of UT1:“UT1 is an angle which is proportional to the sidereal rotation of the Earth, the coefficient of proportionality being chosen so that UT1, in the long term, remains in phase with the alternation of day and night. In some applications, UT1 can be considered as a non-uniform time scale”.

General Principles for the Realization of Reference Systems for Earth Dynamics

1975 ◽  
Vol 26 ◽  
pp. 261-267 ◽  
Author(s):  
G. Veis
Keyword(s):  
Reference System ◽  
Reference Systems ◽  
The Earth ◽  
Direct Measurements ◽  
Planets And Satellites ◽  
Definition Of ◽  
Earth Dynamics ◽  
Dynamic Phenomena ◽  
Selection Of ◽  
Better Than

A reference system is useful to express conveniently the location of a point and to study kinematic and dynamic phenomena. Although the definition of a reference system is theoretically very simple, its realization becomes very fifficult since it must be achieved by measurements reduced and expressed in this system.A referenoe system can be materialized by direct measurements of the coordinates or, more frequently, indirectly by measuring differential quantities and calculating the coordinates “de proche en proche.” The accuracy of the system definition cannot be better than the accuracy of the measurements themselves.For Earth dynamics we need a reference system related to the Earth, but since observations of other bodies such as galaxies, stars, planets, and satellites also may be required, the reference systems in which the positions of these bodies are expressed must also be related to the selected terrestrial system.To optimize the selection of a reference system one must consider both the phase of the operations for the establishment of the system and the phase of the utilization of the system, because the establishment of a reference system is not the final goal.

scholarly journals Use of Gravity Measurements in Defining and Realizing Reference Systems for Geodynamics

1980 ◽  
Vol 56 ◽  
pp. 217-223
Author(s):  
J. D. Boulanger ◽  
N. N. Pariisky ◽  
L. P. Pellinen
Keyword(s):  
Reference System ◽  
Reference Ellipsoid ◽  
Reference Points ◽  
Sufficient Information ◽  
Reference Systems ◽  
The Earth ◽  
Gravity Measurements ◽  
Terrestrial Reference System

AbstractSingle measurements of gravity cannot give sufficient information about the position of measuring points with respect to some terrestrial reference system. Only a set of gravimetric stations all over the Earth combined with a determination of their coordinates allows one to determine (from the solution of Molodensky’s problem) the heights of these stations with respect to a level ellipsoid with center at the geocenter. Given in addition their heights above some reference ellipsoid, whose position in the Earth’s body is fixed through a set of reference points on its surface, the position of the geocenter in the same reference system may be obtained.

scholarly journals Permanent Milliarcsecond Link of Celestial and Terrestrial Reference Systems

1991 ◽  
Vol 127 ◽  
pp. 101-107
Author(s):  
M. Feissel
Keyword(s):  
Reference System ◽  
Artificial Satellites ◽  
Radio Sources ◽  
Reference Systems ◽  
International Earth Rotation Service ◽  
Earth Orientation Parameters ◽  
Long Baseline ◽  
The Earth ◽  
Celestial Reference System ◽  
Orientation Parameters

AbstractThe celestial reference system and the terrestial reference system of the International Earth Rotation Service (IERS) are realized on the basis of observation programs in Very Long Baseline radio Interferometry and laser ranging to the Moon and artificial satellites. The celestial frame is materialized by the equatorial coordinates of radio sources observed in VLBI; the terrestrial frame is materialized by the cartesian coordinates of the terrestrial sites monitored by the three techniques. Series of the Earth Orientation Parameters are derived from the same observations. These series provide a permanent link between the celestial system and the terrestrial system at the level of 0.001”.The global adjustment in which the reference systems are defined and realized is described, and the metrological properties of the frames and of the derived EOP are evaluated.

scholarly journals Reference Systems

1997 ◽  
Vol 165 ◽  
pp. 107-114
Author(s):  
Toshio Fukushima
Keyword(s):  
General Relativity ◽  
Reference System ◽  
World Wide ◽  
Great Care ◽  
Reference Systems ◽  
The World ◽  
Fundamental Astronomy ◽  
Definition Of ◽  
Working Standards ◽  
Physical Phenomena

AbstractA reference system is a relation connecting observables and their mathematical represententions. The principle of general relativity assures that any sort of coordinate system can be used to describe physical phenomena. Thus, any reference system is only a convention. There is no absolutely true reference system. Instead, people seek for abestreference system, whose meaning may differ thus need to clarify. Taking an example from Earth rotation, we discuss how to find such a best reference system. The definition of the best system will change as scientific understandings deepen and computational environments develop. Therefore, we can not stop improving reference systems. However, when replacing an existing widely-spread system, one must take great care to minimize the inconvenience caused by its transition, especially the inconvenience which users might endure. The Standards Of Fundamental Astronomy (SOFA) project being conducted by the IAU WG on Astronomical Standards has the opportunity to ease this troublesome task. The World Wide Web (WWW) will be a main device to realize the project, namely to provide working standards including reference systems to the world.

scholarly journals New Celestial Reference System

1980 ◽  
Vol 56 ◽  
pp. 305-316
Author(s):  
P. K. Seidelmann ◽  
G. H. Kaplan ◽  
T. C. Van Flandern
Keyword(s):  
Reference System ◽  
Reference Systems ◽  
Coordinate Systems ◽  
Strong Link ◽  
The Earth ◽  
Celestial Reference System ◽  
Observational Techniques ◽  
New System ◽  
Astronomical Constants ◽  
Planetary Theories

AbstractThe IAU (1976) System of Astronomical Constants, the FK5 and new lunar and planetary theories are being introduced in 1984. The investigation and planning for the transition has revealed the complex interdependencies between observational techniques and the reference systems, and their strong link to the rotating and orbiting Earth. The inaccuracies in our knowledge of the star positions, astronomical constants and the rotation and motion of the Earth are embedded in subtle ways in the observations and the reference coordinate systems. For example, the FK4 reference system in 1950.0 coordinates rotates with respect to an inertial system. Details are given for the conversion to the new system.

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