Sunspot Catalog (1921–1935) and Area Series (1886–1940) from the Stonyhurst College Observatory

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Abstract A sunspot observation program was started at the end of the 19th century at the Stonyhurst College Observatory (hereafter SCO) by Father Perry, director of the observatory at that time. A digitization of the daily sunspot area series recorded in this observatory from 1886 to 1940 (with a gap between 1889 and 1897) is provided in this work. This depicts one of the oldest sunspot area series available. A comparison of this series with contemporary area series made in other observatories shows that SCO generally recorded larger areas than those in some of the observatories of that time such as, for example, the Royal Greenwich Observatory (RGO). Furthermore, SCO published a sunspot group catalog for the period 1921–1935. We provide a machine-readable version of this catalog. We compared the SCO group number series with other sunspot data obtained from other observatories. In this case, for example, the RGO systematically recorded more groups than the SCO. We compared SCO and RGO area distribution functions obtaining the calibration constant between both data sets. We also obtained the butterfly diagram from the group latitudes recorded by SCO and compared the percentages of group types computed from the SCO catalog with those from Valencia Observatory (following the Cortie morphological classification of sunspot groups), identifying their similarities and differences.