Modern View of the Sun: Materials for an Experimental History at the Dawn of the Telescopic Era

Galileo and the telescope revolutionized the concept of the Sun. The discovery of its rotation was possible due to the continuous observation of the sunspots. The faculae and the maculae with umbra and penumbra became accessible daily to new instruments, leaving the perfectly lucid disk to the realm of symbolism. Was this new view possible before the telescope? Technically, pinhole cameras can show the largest sunspots, as well as the naked eye under very particular conditions. However such observations were too scattered to produce any change in the established understanding of the Sun. Synoptic observations of the largest sunspots of the XXV solar cycle made with the naked eye, pinhole camera, and a telescope in camera obscura are presented and compared with the historical ones. Sunspots could have been discovered in Florence as early as 1475 with the pinhole meridian line of S. Maria del Fiore: the Spörer minimum (1460–1550) of the solar activity prevented it. Indications of white light flares and prominence observations appear in a drawing dated back to 1635, well before the first H-alpha inspections in the 19th century.