Full-disc observations of the Sun in the Ca ii K line provide one of the longest collections of
solar data. First such observations were made in 1892 and since then various sites around …

Context. Full-disc observations of the Sun in the Hα line provide information about the solar
chromosphere, and in particular, about the filaments, which are dark and elongated features …

With the increasing concern about climate change, it is important to have accurate
information on the individual contributions by the potential driving agents, solar variability …

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 …

Context. Knowledge of solar irradiance variability is critical to Earth's climate models and
understanding the solar influence on Earth's climate. Direct solar irradiance measurements …

Context. Reconstructions of past irradiance variations require suitable data on solar activity.
The longest direct proxy is the sunspot number, and it has been most widely employed for …

Observations of the chromosphere with Deslandres's spectroheliograph started at Paris
Observatory in 1893 and were followed by systematic observations at Meudon since 1908 …

Total solar irradiance (TSI) has been monitored from space since 1978, ie for about four
solar cycles. The measurements show a prominent variability in phase with the solar cycle …

Context. Historical Ca II K spectroheliograms (SHG) are unique in representing long-term
variations of the solar chromospheric magnetic field. They usually suffer from numerous …

Context. Studies of long-term solar activity and variability require knowledge of the past
evolution of the solar surface magnetism. The archives of full-disc Ca II K observations that …