1. A uniform coordinate syster 2. A three-dimensional Cartesian system The angle o between the two systems is called The X Greenwich sidereal time system points towards the vernal X,=X The X axis being ortho o both the x.-axis X,-axis of the and the x,-axis completes a right-handed earth-fixed system coordinate frame defined by the ntersection line of the equatorial plane vith the plane represented by the meridian 2.1 A Group of Terms Precession(Sun-Earth-Moon, Fixed! ) Vernal Equinox moves towards west 50.26second. The difference between equinox calendar year and sidereal year 0.014day 2. Coordinate Systems Nutation: The oscillation withrespect to the inertial space (Sun-Earth-Moon, Change! )(p. 27) nutation: Chandler period: The period of the free motion amounts to about 430 days and is known as the Chandler period 1. Conventional Celestial Reference System 2. Conventional Terrestrial Reference System l. Definition of CCRS: p Definition: Terrestrial Reference Frame(TRF)(p. 28) CRF: Since this system is defined conventionally and TRF: is defined by a set of terrestrial control stations the practical realization does not necessarily coincide serving as reference points. Most of the reference stations with the theoretical system, it is called (conventional) are equipped with Satellite Laser Ranging(SLR)or Celestial Reference Frame(CRE Very Long Baseline Interferometry (VLBI) pabilities gorously inertial because of the accelerated motion of the earth around the sun o World Geodetic System 1984(WGS-84 ), 1500 o the International Earth Rotation Service (IERS) called IcRF o ITRF-94 established by the IERS, 180 points2 1. A uniform coordinate system, 2. A three-dimensional Cartesian system -axis of the earth-fixed system is defined by the intersection line of the equatorial plane with the plane represented by the Greenwich meridian. X1 The -axis for the space-fixed system points towards the vernal equinox. 0 X 1 The angle Θ0 between the two systems is called Greenwich sidereal time. The -axis being orthogonal to both the -axis and the -axis completes a right-handed coordinate frame. X1 0 X 1 0 X 1 2. Coordinate Systems Precession (Sun-Earth-Moon, Fixed!!!): Vernal Equinox moves towards west 50.26second, The difference between equinox calendar year and sidereal year 0.014day Nutation: The oscillation with respect to the inertial space is called nutation (Sun-Earth-Moon, Change!!!) (p. 27). 1. Secular precession: 2. Periodic nutation: Polar motion: The oscillation with respect to the terrestrial system is named polar motion. Chandler period: The period of the free motion amounts to about 430 days and is known as the Chandler period. ω 2.1 A Group of Terms 1. Definition of CCRS: p.28. CRF: Since this system is defined conventionally and the practical realization does not necessarily coincide with the theoretical system, it is called (conventional) Celestial Reference Frame (CRF). o "quasi-inertial" means a geocentric system is not rigorously inertial because of the accelerated motion of the earth around the sun. o the International Earth Rotation Service (IERS), called ICRF 1. Conventional Celestial Reference System (p. 28) 2. Conventional Terrestrial Reference System (p. 28) Definition: Terrestrial Reference Frame (TRF) (p. 28) TRF: is defined by a set of terrestrial control stations serving as reference points. Most of the reference stations are equipped with Satellite Laser Ranging (SLR) or Very Long Baseline Interferometry (VLBI) capabilities. X1 o World Geodetic System 1984 (WGS-84), 1500 sites/points o ITRF-94 established by the IERS, 180 points