Fig. A.1.
Examples of historical observations that were excluded from this study. Shown are the raw density images. The plotted examples were taken at the (a): Arcetri (21 March 1941), (b): Kodaikanal (18 March 1990), (c): Mitaka (11 April 1948), and (d): Mt Wilson (17 January 1973) observatories. The images are not compensated for solar ephemeris.
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