Investigation of the Long-term Variation of Solar Ca ii K Intensity. II. Reconstruction of Solar UV Irradiance

Abstract Reconstruction of long-term solar UV variations during the entire 20th century is reported. The sunspot number has been used for this purpose so far. By using full-disk Ca K intensity as an additional proxy, range allowed values reconstructed irradiance becomes more restricted. We use archival data photographic plates digitized at Kodaikanal Solar Observatory. calibration method developed in our previous paper (Paper I) applied. Various proxy activity have to estimate past irradiance. In light context, some issues historical are commented on.