The International Celestial Reference Frame: ICRF
The radio source catalogue which was adopted as the official International Celestial Reference Frame (ICRF) by the IAU at its General Assembly in 1997 belongs to the category of conventional fundamental catalogues. It does not differ fundamentally from the numerous radio catalogues produced during the preceding two decades. This catalogue is merely another member of the category of reference frames produced by the `observable method’ discussed in Sect. 5.5.2. It is revolutionary in the sense that for the first time in history the official coordinate system of astronomy is no longer directly connected to the equinox and the ecliptic plane. In accordance with resolutions adopted by the 1991 IAU General Assembly, materialization of the conventional celestial reference frame is achieved via the coordinates of ‘primary’ or ‘defining’ extragalactic radio sources. What distinguishes the ICRF from its predecessors is the breadth of the data base, the care taken to ensure that only sources of the highest quality were selected as the primary defining objects, and considerable agonization to ensure that the best models were used in the data analysis during a period when substantial improvements in tropospheric and Earth-tidal modelling were rapidly starting to emerge and find acceptance.
KeywordsRadio Source Source Position Extragalactic Radio Source Deep Space Network VLBI Data
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