scholarly journals The Origin of Celestial Coordinates

1990 ◽  
Vol 141 ◽  
pp. 51-59
Author(s):  
C. A. Murray
Keyword(s):  
Earth Rotation ◽  
Zero Point ◽  
Rate Of Change ◽  
Reference Systems ◽  
The Earth ◽  
Private Correspondence ◽  
Rotation Of The Earth ◽  
Right Ascension

In 1978, Guinot proposed that, for studies of Earth rotation, the zero point of the apparent “right ascension” coordinate on the true equator should be so chosen that the rate of change of its hour angle is exactly proportional to the inertial rate of rotation of the Earth. It has been subsequently suggested that this concept of the “non-rotating origin” supersede the equinox quite generally as the origin of celestial coordinates. Since this proposal was first put forward, there has been much discussion, and some criticism, from Aoki and his colleagues, both published and in private correspondence. Some of the arguments for and against Guinot's proposal are discussed, as a contribution to the wider debate on reference systems now being carried out under the auspices of the IAU.

scholarly journals On the eve of the 100th anniversary of IAU Commission 19/A2 “Rotation of the Earth”

2018 ◽  
Vol 13 (S349) ◽  
pp. 325-331
Author(s):  
Zinovy Malkin ◽  
Richard Gross ◽  
Dennis McCarthy ◽  
Aleksander Brzeziński ◽  
Nicole Capitaine ◽  
...  
Keyword(s):  
Earth Rotation ◽  
Reference Frames ◽  
International Association ◽  
General Assembly ◽  
Reference Systems ◽  
Standing Committee ◽  
Earth Orientation ◽  
Terrestrial Reference Frames ◽  
The Earth ◽  
Rotation Of The Earth

AbstractIAU 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 been among the primary Commission topics. In 1987, the IAU through Commissions 19 and 31 “Time” established, jointly with the International Union of Geodesy and Geophysics, what is now known as the International Earth Rotation and Reference Systems Service. Commission 19 continued to work to develop methods to improve the accuracy and understanding of Earth orientation variations and related reference systems and frames as well as theoretical studies of Earth rotation. In 2015, Commission 19 was renewed as Commission A2 “Rotation of the Earth” continuing Commission 19’s functions and linking the astronomical community to other scientific organizations such as the International Association of Geodesy, International VLBI Service for Geodesy and Astrometry, International GNSS Service, International Laser Ranging Service and International DORIS Service. During its entire history, IAU Commission 19/A2 has always worked in close cooperation with these and other related services to improve the accuracy and consistency of the Earth orientation parameters and celestial and terrestrial reference frames.

The Terrestrial Coordinate System and International Earth-rotation Services

1985 ◽  
Vol 38 (02) ◽  
pp. 216-217
Author(s):  
G. A. Wilkins
Keyword(s):  
Coordinate System ◽  
Earth Rotation ◽  
Reference System ◽  
New Techniques ◽  
Crustal Movements ◽  
Earth Observations ◽  
The Earth ◽  
External Reference ◽  
External Objects ◽  
Rotation Of The Earth

New techniques of measurement make it possible in 1984 to determine positions on the surface of the Earth to a much higher precision than was possible in 1884. If we look beyond the requirements of navigation we can see useful applications of global geodetic positioning to centimetric accuracy for such purposes as the control of mapping and the study of crustal movements. These new techniques depend upon observations of external objects, such as satellites or quasars rather than stars, and they require that the positions of these objects and the orientation of the surface of the Earth are both known with respect to an appropriate external reference system that is ‘fixed’ in space. We need networks of observing stations and analysis centres that monitor the motions of the external objects and the rotation of the Earth. Observations of stars by a transit circle are no longer adequate for this purpose.

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 Basic Problems in the Kinematics of the Rotation of the Earth

1979 ◽  
Vol 82 ◽  
pp. 7-18 ◽  
Author(s):  
Bernard Guinot
Keyword(s):  
Earth Rotation ◽  
Rotation Axis ◽  
Earth’S Rotation ◽  
International Astronomical Union ◽  
Earth's Rotation ◽  
The Earth ◽  
International Astronomical ◽  
Rotation Of The Earth

With the advent of more precise methods for measuring Earth rotation, a number of corrections to the apparent directions in space, to the terrestrial references, and to the rotation axis motion have to be carefully applied. It is the duty of the international Astronomical Union to give recommended or conventional expressions of these corrections in order to avoid inextricable difficulties in discussing the evaluated results. However, this task is not sufficient. The concepts used in the description of the Earth's rotation are somewhat obscured by traditions. They should be purified by removing notions which are not directly relevant.

scholarly journals Review of the achievements of project MERIT for the intercomparison of techniques for monitoring the rotation of the Earth

1988 ◽  
Vol 128 ◽  
pp. 227-232
Author(s):  
G. A. Wilkins
Keyword(s):  
Earth Rotation ◽  
Working Group ◽  
New Techniques ◽  
New Methods ◽  
The Earth ◽  
Terrestrial Reference System ◽  
Rotation Of The Earth ◽  
Analyse Data ◽  
Set Up ◽  
International Services

It is generally recognised that the Working Group on the Rotation of the Earth that was set up after IAU Symposium No. 82 has successfully achieved its principal objectives, namely: “to make recommendations on … future international services on earth-rotation” and “to obtain and analyse data on earth-rotation by both current and new methods …”. In particular, by organising Project MERIT, it has stimulated the development and use of new techniques and it has brought together in fruitful collaboration scientists from many countries and disciplines. Other subsidiary objectives have also been achieved and the project has been extended through cooperation with the COTES Working Group on the terrestrial reference system. The possible reasons for this success are also reviewed in the expectation that the conclusions will be relevant to other future projects.

Time Determination and Time Keeping

1948 ◽  
Vol 1 (2) ◽  
pp. 109-117
Author(s):  
Harold Spencer Jones
Keyword(s):  
Frequency Control ◽  
Rate Of Change ◽  
Time Interval ◽  
The Earth ◽  
Convenient Means ◽  
Time Signals ◽  
Time Determination ◽  
The Mean ◽  
Rotation Of The Earth ◽  
Definite Manner

The rotation of the Earth provides the ultimate standard of time. As the fundamental unit of time we can use either the mean solar day or the sidereal day; these two units are related in a definite manner, so that when one is determined, the other can be inferred. The purpose of any timepiece is to subdivide the day into shorter intervals, and so give the time at any instant. No timepiece will give exact time; the error of the timepiece at some definite instant and the rate of change of that error, or, briefly, the rate, must be determined in order to extrapolate for the correct time at some subsequent instant. The accuracy of the extrapolation will depend upon the uniformity of the rate of the timepiece. Radio time signals sent out from an observatory, which is responsible for the determination and distribution of time, provide the most convenient means for deriving the error and rate of a timepiece. For normal navigational purposes an accuracy of about 0·05 seconds is adequate. But for the purpose of frequency control a very much higher precision is needed—but a precision in time interval rather than in absolute time. Some of the radio-aids to navigation depend upon the accuracy in standardization of frequency, so that high accuracy in time interval has become, indirectly, a navigational requirement.

scholarly journals COMMISSION 19: ROTATION OF THE EARTH

2008 ◽  
Vol 4 (T27A) ◽  
pp. 37-49
Author(s):  
Aleksander Brzezinski ◽  
Chopo Ma ◽  
Véronique Dehant ◽  
Pascale Defraigne ◽  
Jean O. Dickey ◽  
...  
Keyword(s):  
Earth Rotation ◽  
Reference Frames ◽  
International Association ◽  
Vice President ◽  
Past President ◽  
Scientific Investigations ◽  
The Earth ◽  
International Vlbi Service ◽  
Commission President ◽  
Rotation Of The Earth

The Commission supports and coordinates scientific investigations in the Earth rotation and related reference frames. Several changes had been introduced to the structure of Commission 19 since the IAU XXVI General Assembly in Prague, 2006. The Organizing Committee of Commission 19 has been substantially reduced. It consists now of six ex-officio members, the Commission president, vice-president, past president and representatives from the International Association of Geodesy (IAG), International Earth Rotation and Reference Systems Service (IERS), International VLBI Service for Geodesy and Astrometry (IVS), and five members at-large who are nominated by the OC, selected by the Commission members and elected by the IAU GA for a maximum of two terms. The modified terms of reference of Commission 19, the list of members and other details can be found at the Commission website <iau-comm19.cbk.waw.pl/>.

scholarly journals 19. Rotation of the Earth (Rotation de la Terre)

1976 ◽  
Vol 16 (1) ◽  
pp. 105-116
Author(s):  
C. Sugawa ◽  
R. O. Vicente ◽  
H. J. M. Abraham ◽  
P. L. Bender ◽  
M. H. Cohen ◽  
...  
Keyword(s):  
Earth Rotation ◽  
The Earth ◽  
Rotation Of The Earth
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