The Course of Preparation and Manufactary of the LLMC

The preparation and development of the LLMC were carried out under the condition of high precision astrometry.The traditional meridian circles have their limitations in the observational principle and they also have the shortages of measuring and modifying their instrumental errors.A new observational principle has been developed, some new methods of measuring and modifying the instrumental errors have been found in the course of preparation and manufactary of the LLMC.Firstly, a new method of absolute measurement using meridian circle was discussed.In detail, after recording the moments of a star crossing the meridian and the prime vertical, respectively the azimuth error of the instrument can be obtained.On the other hand, the reco rded moments of the same star in the prime vertical and the zenith distance in the meridian can be used to solve the instant latitude.Besides, the instant absolute refraction can be determined by means of the apparent zenith distance observed in the prime vertical.These principles have been successfully tested on a modified transit instrument.Secondly, some methods of measuring all instrumental erro rs in real time were found.As these instrumental errors were all determined in real time, there is no need to introduce any other erro r correction mode.The meridian circle was desig ned in Shanghai Observatory and manufactured in Nanjin Astronomical Instrument Research ceter.In the August of 1996, the instrument w as installed in Yunnan Observatory.Preliminary observations begin now after the adjustment and development for about one year.