Topics No.1

Historical Ca K Spectroheliograms Available Online

The Solar Observatory is pleased to announce the online availability of the digitized historical Ca K full-disk Spectroheliograms taken from 1917 through 1974, //solarwww.mtk.nao.ac.jp/en/db_ca.html. The observation has been done with a Grubb 30-cm sidelostat and a Toepfer double-prism Spectroheliograph for about 8500 observing days at the Tokyo Astronomical Observatory. Basically one scan was carried out per day, and the images were recorded on photographic plates (-1960) and 35mm films (1960-). Along with the Kodaikanal, Mt. Wilson, and Arcetri data, our Ca K images will help to reproduce the solar magnetic activity during recent 100 years.

Fig.1 Cyclic solar activity variation in the former half of the 20th century shown by Ca K spectroheliograms.	Fig.2 Photographic plates, on which the Ca K spectroheliograms are recorded.
Fig.3 The sidelostat (Left) and the spectroheliograph (Right), which have been working at the Mitaka Campus of the NAOJ (photos provided by the Archive Office, Public Relations Center).

Nov. 15, 2011