Analysis of Solar Diameter Measurements Made at the Basilica of San Petronio during and after the Maunder Minimum

A series of measurements of the solar diameter taken in the meridian line of the Basilica of San Petronio (Bologna, Italy) between 1655 and 1736 has been analyzed. This series is of interest because the measurement period includes the Maunder Minimum (1645–1715; hereafter MM) when solar activity was abnormally low. Some authors have suggested an increase of the solar diameter during the MM. Trying to detect these changes, statistical analyses comparing measurements taken in San Petronio during the MM (1655–1715) and other ones taken in a subsequent period (1716–1736) have been performed. Mann–Whitney U tests and Student’s t-tests indicate that there is no statistically significant difference in the medians and averages of the solar diameter in both periods. In fact, we have found differences around 0.″6 in the medians and the averages, which are below the mean accuracy of the instrument. Therefore, we conclude that there is no difference between the solar diameter value measured during the MM (1655–1715) and that for the subsequent period 1716–1736. This implies that there has not been an increase in the solar diameter of several arcseconds during the MM as has been speculated by some authors.