  Sunspot catalogs are very useful for studying the solar activity of the
recent past. In this context, a catalog covering more than three solar cycles
made by the astronomers of the Madrid Astronomical Observatory in Spain
(nowadays, the National Astronomical Observatory) from 1952 until 1986 has been
recovered. Moreover, a machine-readable version of this catalog has been made
available. We have recovered abundant metadata and studied the reliability of
this dataset by comparing it with other sunspot catalogs.
