COMPARISON BETWEEN ORIENTAL AND OCCIDENTAL SUNSPOT OBSERVATIONS

The reliability of sunspot sightings recorded in various Oriental hist ories is assessed by comparing carefully the Oriental sunspot sighting s from 1862 onwards with contemporaneous Occidental white-light images of the Sun acquired by the Royal Greenwich Observatory (RGO). As a pr erequisite to this comparison, a simple procedure is developed for pro ducing 'approximate reconstructions' of the white-light photographs of the Sun obtained by the RGO during the interval 1874 May 09-1976 Dece mber 31. The approximate reconstructions are based on precise measurem ents of the positions and areas of sunspots on the solar photographs, which have been published in tabulated form as the Greenwich Photoheli ographic Results: 1873-1976. This reconstruction procedure is extremel y important for the photoheliographic observations in the interval 187 4-1917, because the number of days for which approximate solar images can be reconstructed significantly exceeds the number of days for whic h contact prints of the original observations are available. The recon structed solar images constitute a valuable homogeneous series of 'obs ervations' that illustrates long-term Variations in sunspot activity. Both reconstructed solar images and original contact prints are used t o confirm that the dates of the Oriental sunspot sightings quoted in t he various histories are largely correct. Therefore, these dates can b e used with some confidence in statistical studies which are not obvio usly invalidated by the sparseness of the Oriental sunspot sightings.