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Full disc observations of the Sun in the H$\alpha$ line provide informationabout the solar chromosphere and in particular about the filaments, which aredark and elongated features that lie along magnetic field polarity inversionlines. This makes them important for studies of solar magnetism. Since fulldisc H$\alpha$ observations have been performed at various sites since 1800s,with regular photographic data having started in the beginning of the 20thcentury, they are an invaluable source of information on past solar magnetism.In this work we aimed at deriving accurate information about filaments fromhistorical and modern full disc H$\alpha$ observations. We have consistentlyprocessed observations from 15 H$\alpha$ archives spanning 1909-2022. Our dataprocessing includes photometric calibration of the data stored on photographicplates. We have constructed also Carrington maps from the calibrated H$\alpha$images. We find that filament areas are affected by the bandwidth of theobservation. Thus, cross-calibration of the filament areas derived fromdifferent archives is needed. We have produced a composite of filament areasfrom individual archives by scaling all of them to the Meudon series. Ourcomposite butterfly diagram shows very distinctly the common features offilament evolution, that is the poleward migration as well as a decrease in themean latitude of filaments as the cycle progresses. We also find that duringactivity maxima, filaments on average cover about 1% of the solar surface. Wesee only a weak change in the amplitude of cycles in filament areas, incontrast to sunspot and plage areas. Analysis of H$\alpha$ data for archiveswith contemporaneous Ca II K observations allowed us to identify and verifyarchive inconsistencies, which will also have implications for reconstructionsof past solar magnetism and irradiance from Ca II K data.

Analysis of full-disc H alpha observations: Carrington maps and filament properties in 1909-2022