Sunspot Numbers and Areas from the Madrid Astronomical Observatory (1876-aEuroparts per thousand1986)

The solar program of the Astronomical Observatory of Madrid started in 1876. Observations were made in this institution to determine sunspot numbers and areas for ten solar cycles. The program was completed in 1986 and the resulting data have been published in various Spanish scientific publications. Four periods of this program (with different observers and instruments) were identified with the aid of the interesting metadata that has been made available. In the present work, the published data were retrieved and digitized. Their subsequent analysis showed that most of these data could be considered reliable given their very high correlation with reference indices (international sunspot number, group sunspot number, and sunspot area). An abrupt change emerged in the sunspots/groups ratio in 1946, which lasted until 1972.