We report progress on the ongoing recalibration of the Wolf sunspot number (SN) and group-
sunspot number (GN) following the release of version 2.0 of SN in 2015. This report …

Context. Studies and reconstructions of past solar activity require data on all magnetic
regions on the surface of the Sun (ie on dark sunspots as well as bright faculae–plage and …

Abstract Angelo Secchi, an Italian Jesuit and prominent scientist of the 19th century, and one
of the founders of modern astrophysics, observed the Sun regularly at the Collegio Romano …

Solar activity has been subject to increasingly more research in the last decades. Its
influence on life on Earth is now better understood. Solar winds impact the earth's magnetic …

Abstract The Astronomical Observatory of the University of Coimbra has a huge collection of
solar images, acquired daily since 1926. From the beginning, only spectroheliograms in the …

Solar differential rotation is an important ingredient of the solar dynamo model, not only
because the solar rotation profile is one of the key inputs in a solar dynamo model, but also …

Abstract The Astronomical Observatory of the University of Coimbra (Portugal) published a
catalog with solar observations such as sunspots, faculae, prominences, and filaments for …

A sunspot catalog was published by the Madrid Astronomical Observatory from sunspot
observations made by Rafael Carrasco and his assistants for the period November 1931 …

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 complete dataset of sunspot drawings recorded at Sacramento Peak Observatory (SPO)
from late 1947 till mid-2004 has been digitized. We present the history of the observations …