The Umbra–Penumbra Area Ratio of Sunspots During the Maunder Minimum

Abstract

The Maunder Minimum (MM) was a prolonged period of low solar activity that occurred between 1645 and 1715. The true level of solar activity corresponding to this epoch is still a matter of debate. In order to compare solar activity during the MM with that of other epochs, we have evaluated the umbra-penumbra area ratio (U/P hereafter) during the MM. Thus, we have analyzed 196 sunspot drawings including 48 different sunspots observed during the period 1660-1709. The mode value of the ratio obtained from the occurrence frequency distribution lies between 0.15 and 0.25. Furthermore, the median and mean values are equal to 0.24 ± 0.07 and 0.27 ± 0.08 with a sigma clipping, respectively. These results are consistent with recent research using more modern data. Higher U/P values mean faster sunspot decay rates. From our results, the almost absence of sunspots during the Maunder Minimum could not be explained by changes in the U/P since the values of the ratio obtained in this work are similar to values found for other epochs.

Soonspot: Software to Determine Areas and Sunspot Positions

“…Moreover, we have calculated the average of the umbra-penumbra ratio for all the sunspots obtaining a value equal to 0.26. This value agrees with works carried out in order to study this ratio both during the Maunder Minimum (Carrasco et al, 2018) and other epochs (Steinneger, 1990;Vaquero et al, 2005).…”

Historical sunspot records

“…Instead of the absolute spot area, the ratio of penumbral to umbral area may be an interesting quantity, as it suffers less from the scale problem and is also applicable to drawings which do not show the entire solar disk. The evolution of this quantity over time has not been studied much; an attempt was made for the Maunder minimum by Carrasco et al (2018a) and compared with data from de la Rue of 1862-1866 (Vaquero et al 2005, see also references therein).…”

“…Only some morphological details can be recovered and, in general, the area of the spots in these drawings cannot be evaluated due to problems of scale and perspective. However, the observations do contain the ratio of umbral to penumbral areas, for example, which was analyzed from such observations by Carrasco et al (2018a) for spots observed during the Maunder minimum.…”

Solar Activity According to Observation Data by Cigoli, Galilei, Colonna, Cologna, and Scheiner in 1612–1614

“…Для того чтобы судить о модах солнечной цикличности [1] на вековых масштабах, необходимо привлекать для научного анализа исторические астрономические архивы [2-4]. В настоящее время ведется активная работа по восстановлению параметров солнечной активности по зарисовкам солнечного диска в XVII и XVIII веках [5][6][7][8][9][10].…”