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Illustration of the solar observations made by Secchi on 23 July 1871 between 8:30 and 9:55 am. Prominences (white regions from solar limb numbered from 1 to 17), sunspots (black regions on the solar disc), and faculae (white regions on the solar disc) were recorded. Inclined black lines indicate the solar axes (“Est” means East, “Ouest” is West, “Pole N.” and “Pole S.” indicate the solar north and south, respectively). The horizontal black lines are upper line – a reference indicated by Secchi to obtain the position of the celestial equator, and lower line – its parallel diameter given by “a–b” line representing the celestial equator [source: Secchi, 1875, p. 131].
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