Periodicities of the de la rue Sunspot Area Measurements

In the 19th century De la Rue, Stewart, and Loewy carried out a compilation of drawings and photographs of the solar sunspots corresponding to the interval 1832–1868. Using these drawings and photographs, they determined fortnightly values of the percentage of the solar photosphere covered by the sunspots. In this work, we have performed a spectral analysis of these data in order to determine possible periodic signals. In addition to the 11-year solar cycle, short cycles of about 330 days and 30–50 days have been recovered, lacking the 150–160 days period discovered by other authors using several solar activity indicators.     

Identification of Possible Intense Historical Solar Storms During the Years 1781–1788 Inferred from Aurorae and Geomagnetic Observations in Rio De Janeiro

The reconstruction of solar activity during the late 18th century is a puzzle for researchers due to the scarcity of sunspot observations in that epoch. In this work, we analyse some details of the solar activity during the years 1781–1788, inferred from geomagnetic measurements and visual observations of aurorae performed by the Portuguese scientist Bento Sanches Dorta from Rio de Janeiro. We describe in greater detail four large solar storms that induced large changes in daily values of geomagnetic declination and, simultaneously, correspond to visual observations of aurorae described by Sanches Dorta.     

Evidence for a sunspot in A.D. 939 in an Arabian Source

It is the purpose of this paper to present evidence concerning the appearance of a sunspot in A.D. 939 observed by Arabs from the Iberian Peninsula. The sunspot record appears in the Arab source known as al-Muqtabis V.     

Sunspot Catalogue of the Valencia Observatory (1920 – 1928)

A sunspot catalogue was maintained by the Astronomical Observatory of Valencia University (Spain) from 1920 to 1928. Here we present a machine-readable version of this catalogue (OV catalogue or OVc), including a quality-control analysis. Sunspot number (total and hemispheric) and sunspot area series are constructed using this catalogue. The OV catalogue data are compared with other available solar data, demonstrating that the present contribution provides the scientific community with a reliable catalogue of sunspot data.