The Course Changes of Development of the LLMC

The purposes of the LLMC(Lower Latitude Meridian Circle)is to meet new demands and the development of astrometry.In the seventies,the fundamental catalogues were all compiled by the observations obtained by traditional meridian circles in high latitude regions, some systematic errors were variable with the changes among different sky regions existed in the catalogues,and the observational purpose of LLMC was to connect both observations obtained by traditional meridian circles in the south and north hemispheres and to develope the fundamental catalogue. In the middle of eighties,extragalactic radio reference frame appeared.As this frame is not available for the optical observation,the stellar positions observed by the LLMC were designed by means of the method of CCD plate overlapping to be connect with the positions of extragalactic bodies.Therefore,the absolute proper motions of some stars could be determined and a stellar reference frame could be transfered into a quasi-inertial reference frame.At the beginning of ninties,the Hipparcos satellite began to observe,and some traditional meridian circles were equipped with CCDs to do relative measurements.It is the time to observe the absolute positions of extragalactic bodies and stars by the LLMC equipped with CCD and construct directly a quasi-inertial reference frame.Furthermore,the observations can provide some useful information about our solar system, stars galaxies for astrophysics and geophysics.