Greenwich Photo-heliographic Result (GPR)
The historical volumes of Greenwich Photo-heliographic Result (GPR) include daily measurements of sunspot positions and the areas of sunspots and faculae observed from 1874 to 1976. Prior to 1948 the GRP volumes were published by the Royal Observatory, Greenwich and thereafter by the Royal Greenwich Observatory. In 1976 the program of daily solar observations was transferred to the Debrecen Observatory of the Hungarian Academy of Sciences. Included at this website are digitized versions of the original GPR publications and tabular lists derived from the original data. A program is underway to identify and correct errors in the original datasets.