Published online by Cambridge University Press: 14 August 2015
Recent absolute and differential observations of fundamental stars have indicated the need for a revision of the fundamental reference system represented by the positions and proper motions of the FK4. The revision of the FK4 will be based on modern fundamental and differential observations of high accuracy which allow (a) the extension of the FK4 to fainter stars, (b) the improvement of the system, (c) the derivation of individual corrections to positions and proper motions, and (d) the determination of the equinox and its motion. The completion of the programme, resulting in the FK5 and a Supplement giving data in the system of FK5 for bright stars and faint objects (including optical counterparts of radio sources), may be expected about 1980.
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