Greenwich Observations of the Horizontal and Vertical Diameters of the Sun

Abstract

It has been claimed that the Greenwich observations of the horizontal diameter of the Sun are in agreement with those made at Campidoglio and Monte Mario in indicating a real variation of diameter with a period of about 22 years. It is shown in the present paper that this conclusion cannot be justified from the data considered. A more detailed analysis of the Greenwich measurements of both the horizontal and vertical diameters in the period 1915 to 1936 is given, in which corrections are applied for irradiation and personality differences between observers. The resulting diameters show comparatively large variations from year to year. These variations do not necessarily represent real changes in the size of the Sun; they may be due to variations in the mean personality correction. No definite relationship can be established between the apparent variations in diameters and other phenomena, such as the sunspot cycle.