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The fundamental reference of the Earth rotation observation by the method of optical astrometry, such as VZT, PZT, astrolabe, transit instrument and so on, relies upon the stellar system. Hence the stellar positions and proper motions, and the celestial reference coordinate system are essential to preserve the system of the Earth orientation parameters determined by the optical astrometry.
The earth rotation parameters and coordinates of optical astrometric stations from 1962. O to 1986. O are estimated simultaneously on the assumption that the system of selected standard stations does not rotate. Longitudes and latitudes of the stations are determined every 2 months. Disagreement of the ERPs with those obtained by the space techniques decreased much compared with the published ERPs of the IPMS. It is expected that the ERPs in the whole period are also improved significantly.
The history of the International Latitude Service and the International Polar Motion Service is described, with an emphasis on the evolution of the international cooperation for monitoring the Earth’s rotation. Also given is a brief description of the history of the Japanese geodetic and astronomical activities, as well as the future prospects.
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